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Old 12-18-2017, 12:08 AM   #1
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Default A unique Li-ion Campervan Build..

I've been impressed with the depth of knowledge and thoughtful conversation on the Forum - so thought I would throw out my idea for an 'all electric' camper van build that I had been thinking of building.

The Idea
I'd use diesel or gasoline for cabin heat (Espar or Webasto type) with the goal being a 'single fuel' vehicle (no propane). Water heating, cooking (inductive cook top, microwave, and toaster oven), cooling (optional A/C), fridge, and all kinds of other accessories would be powered good old 110V AC. This would be enabled by a 2.5KW or possibly 3.5KW 48V DC power inverter with a bank of 14 Serial 5 Parallel (14S5P) NCA (Li-aluminum) 18650 batteries - 52V nominal voltage with a charge voltage of 58V. The battery banks will all be inside the heated part of the van and each group of cells will be protected with a BMC (battery management controller). There would still be a smallish AGM 12V cabin battery to handle the things that are not big power drains - this would be charged by the engine's alternator and (optionally) a solar system.

Advantages of this approach
* Simple design: Using mostly 'off the shelf' 110V appliances would save hundreds of $$ which could be used to fund the slightly more expensive battery bank. Appliances would be easily installed using common household wiring within the van. Much easier than routing propane, fitting tanks, and dealing with hazards like open flames. Plus, everything switches over to shore power easily. Lithium batteries are much smaller and lighter in terms of energy density than lead acid, so they can easily be placed into nooks and crannies on the interior of the van rather than locating a large bank of lead acid batteries inside or under the van.

* Lower Cost: Many people seem to think lithium is expensive. Many the current offerings offered by new high end RV makers are expensive, but I think a lot of those costs are due to an in-efficient design rather than inherent costs of lithium. I'll break down some cost estimates below, but my estimates show a very capable system for much less cost.

* Better Reliability: RV appliances are complex, usually because they are designed to operate with various types of power (110V, 12V, and sometimes propane). Standard 110V appliances are very common and easy to service.

*Peace and tranquility!: No annoying generators to deal with. Silent appliances. Fewer systems to manage.

Cost Estimates
First I'd bring up the subject of 'usable power'. Lithium has a big advantage over lead-acid in that you can reliably use at least 80% (or more!) of it's capacity. For longevity reasons, I only run my lead-acid batteries to 50% state of charge. So for argument sake, if I have 200ah of AGM installed; I would call that 1.2KWh of 'usable power' (200Ah * 12V *.5 = 1,200Wh). By comparison, my 14 Series 5 Parallel (14S5P) Lithium bicycle battery would have approx 696Wh of 'usable power' (50.4V * 17.25Ah *.8 = 695.5Wh).

So if my minimal system would require the equivalent of about 400Ah of conventional lead acid house batteries; I could build that with four of my bicycle batteries.
* 400Ah of Lead Acid usable power ~= 2.4KWh usable
* Four of my 14S5P Lithium batteries ~= 2.78KWh usable

My bicycle battery is built with 70 Panasonic 18650 GA cells. These are great cells, that have good capacity and provide lots of current per cell (10A / cell).
For the campervan application I would use the LG F1L 18650 cell or a similar NCR style battery since it's lower cost and has great capacity. It just doesn't support high drain applications (only about 5A / cell), but should be fine for this.

The 2.8KWh battery would require 280 cells total (4 batteries of 70 cells each), 4 bms boards, various nickel weld strips and battery holders, and several hours of labor.

280 cells = 280 * $3.78/cell = $1,059
4 bms boards @ $27 each = $108
Nickles stips, battery holders, shrink wrap, solder, etc. $25

So the Lithium battery would be about $1,200.

Four Group 31 AGM batteries; Trojan 31-AGM's (100aH) are listed at $270 ecah online.

4 100aH batteries = 4 * $270 = $ 1,080

This Lithium battery would only be 11% more expensive than the AGM equivalent (assuming your labor was free). However the Lithium battery is expected to last many more cycles than the AGM battery. When you factor in the lighter weight and smaller size; the lithium battery looks really good.

Here is where the idea really shines. Say all of these appliance require much more power. You could double the 'usable power' for another $1,200 or even triple it for an additional $2,400 and still manage to find places for all 12 of these batteries inside. Locating 12 of the heavy AGM batteries in the van would be hard and really weigh it down.

Inverter: I'd consider the COTEK 3500 Watt 48V PSW Inverter with Transfer Switch for $1,100. Having the x-fer switch for shore power integrated makes a lot of sense. This inverter would probably do the job for the loads mentioned above plus occasional A/C when used carefully (not at the same time as other heavy loads).
https://invertersrus.com/product/cotek-sd3500-148/

I think this inverter would only be $2-300 more than a good 2,000 Watt inverter that you would probably buy anyway for a campervan.

Other cost factors:

* Inductive cooktop: ~$75 vs ~$150 and up for propane cook top
(Then think of all of the cost and complexity of adding propane)
OR: a diesel or gasoline cook top - but that will add around $1K

* Water heater: $160 for a Bosh 1400W 4 gallon electric vs $430 (and up!) for an Atwood 6 gallon propane (with electronic ignition)

* Fridge: Small residential fridge ~$150 vs ~$800 for a 12V/110V compressor fridge.

Charging:

This is more complicated. Ideally, you would like to be able to charge the big house battery quickly. But that is not that easy, especially when boondocking.

I've been thinking of two solutions for this, both have their tradeoffs;

1. Easiest: Get the truck with the biggest alternator you can. My Promaster has a 220A alternator and I think you can get similar ones for the Sprinter and the Ford Transit. Then connect a basic high wattage inverter to heavy cables like this one;

Aims 3,000W inverter $280
https://invertersrus.com/product/aims-pwrinv300012120w/

From that you can run standard 110V battery chargers for the Lithium batteries. So for my example, I would need 4 14S Lithium battery chargers ($100 each). The charger below would charge this battery off the OEM alternator in just over 3 hours. Not great, but probably workable.. Because these batteries scale, if I had twice as much battery; I would just need 8 of these chargers rather than 4 and it would still take about 3.5 hours to charge.

https://lunacycle.com/batteries/char...ebike-charger/

So this 'easy' solution would cost me about $680 to $1,080 depending on the size of the battery.

2. Harder ( but cooler!) solution: Add a second alternator that was just for charging the big Lithium battery - like the Hymer underhood generator. But unlike Hymer, go the route that Advanced RV did and run it at a higher voltage. There are two challenges here. First getting a bracket for the 2nd alternator and fitting it. Hard, but not too hard. Second, sourcing a high DC voltage alternator. These are not common. I think the voltage regulator could be be modified on a good quality 'commodity alternator to create a 58V DC output. This is a topic I have looked into for a while and think it's worthy of a whole separate thread. But if you think about it, a 100A alternator would be producing 5.8KW! That's a lot of juice! You could charge your battery quickly and still have power to run your inverter. It's spec'd to handle over 60V.

Price for this solution is TBD. But it shouldn't be much more than the simple solution above. Bracket, commodity alternator, and the hard part - custom voltage regulator.

Battery Chemistry

Almost every Lithium RV example I've seen to date is using Lithium Phosphate LiFEPO4. I understand why they do this; they are trying to mimic the traditional 12V Lead Acid battery. The primary advantage is to solve the charging issue. But as I demonstrated above, you can still address the charging issue with an inverter and 110V charger (not pretty, but it works). Many go with the 2nd alternator anyway, and there I think it makes more sense to go with a higher voltage. Once you make that decision, the cell voltage no longer matters.

NCR batteries are superior to IFR batteries in so many ways I just don't see why you would choose them.

Safety

One of the topics that always comes up with new ideas is safety, and for good reason. We've all heard stories of exploding Lithium batteries. What could be worse for an RV application? What about exploding propane tanks? Or the silent killer, Carbon Monoxide? While it's true that the Lithium cells can be volatile; it's almost always due to over or under charging. This is what the BMS addresses. Therefore, I think it's better to have a NCR battery protected with a BMS than an unprotected IFR battery (and I've seen this).

The other issue is a pierced or ruptured battery. Though this can happen, the only videos of really violent explosions that I've seen usually involve overcharging the battery way above it's limit (and modern ones don't explode when this happens by the way), then piercing it with a shop press. Piercing a battery with a standard charge doesn't result in much of a show. Given the way that I would place the batteries in the coach, I wouldn't expect them to be pierced any more than I would expect a propane tank to be ruptured.

I can't think of a single electric car that is using IFR batteries. These cars are moving around *much* bigger batteries that are far more exposed than the proposed RV battery. If collisions were such a threat for battery explosions, you would hear a lot more about this.

I've been riding my e-bikes off road in very harsh conditions and then charging them back up in my camper van. The batteries have been in very rough conditions and all kinds of weather and have held up remarkably well.

I think the lithium battery would make an awesome camper van. What are your thoughts?
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Old 12-18-2017, 02:35 AM   #2
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Plenty of RVs already using Lithium batteries.


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Old 12-18-2017, 05:29 AM   #3
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Originally Posted by kite_rider View Post
2. Harder ( but cooler!) solution: Add a second alternator that was just for charging the big Lithium battery - like the Hymer underhood generator. But unlike Hymer, go the route that Advanced RV did and run it at a higher voltage. There are two challenges here. First getting a bracket for the 2nd alternator and fitting it. Hard, but not too hard. Second, sourcing a high DC voltage alternator. These are not common. I think the voltage regulator could be be modified on a good quality 'commodity alternator to create a 58V DC output. This is a topic I have looked into for a while and think it's worthy of a whole separate thread. But if you think about it, a 100A alternator would be producing 5.8KW! That's a lot of juice! You could charge your battery quickly and still have power to run your inverter. It's spec'd to handle over 60V.
You will also have to include a DC-DC converter to operate your 12 volt appliances. Advanced RV is selling their 48V test vehicle which might cost less than putting this together yourself.
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Old 12-18-2017, 01:57 PM   #4
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The Truma Combi works as both house heater and water heater. The same unit can be switched between the chassis engine gas tank or electricity (110v). Would eliminate the need for two separate units.

AFAIK no-one worries about LiFePO4 exploding. For that matter, if you want an explosion-free vehicle, it's more important to go with diesel than to eliminate the propane tank. Gasoline actually has a wider range of flammability and lower ignition temperature than propane. (80*-300*F vs 920*-1020*F)

Here's a demonstration video (purely for entertainment purposes.)

https://www.youtube.com/watch?time_c...&v=18Xn-jTNufo

And here is a fairly clear tutorial on various Li-Ion:

Types of Lithium-ion Batteries ‚€“ Battery University

Good luck with your build - it sounds interesting.
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Old 12-18-2017, 04:31 PM   #5
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.

Exploding RV propane tanks?




They are as rare as exploding RV lithium batteries.

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Old 12-18-2017, 06:16 PM   #6
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.

Exploding RV propane tanks?

They are as rare as exploding RV lithium batteries.
I think the vast majority of fires that are called "propane fires" are really fires caused by having an open propane flame burning at the gas station, rather than a failure of the propane system itself.
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Old 12-18-2017, 06:20 PM   #7
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There a few issues I see here:

Pack Assembly: If you plan on 280 cells, you'd be looking at a 14S20P config. I wouldn't bother making 4 different batteries. Just assemble as one large battery as that will make your BMS easier to manage. But be careful with the cells you selected as if they are only rated for 5amps, your max draw is going to be 5 amps X 20 = 100amps. You are still fine as your max amps at 48V with that 3500w inverter is going to be 80 amps but you are at the top end of that spec.

Time: Assembling a 280 cell battery is going to take a lot of time and if you mess up the soldering of your cells, it's going to bring down the capacity of the entire pack.

Cycle Life: NCR cells are only rated to around 500 cycles at the rate you are talking about draining them 20% compared to lifepo4 at around 3000.

12V vs 48V: As you've mentioned, you are going to have a very hard time charging. Going from DC to AC then back to DC you're losing a lot of efficiency. Plus making your setup very difficult. Now inverting 48V DC to 110V AC is much more efficient IF YOU USE GOOD QUALITY PARTS! I'm not knocking the cotek as they are cheap but still good, but a magnum inverter at 12V is about 89% efficient. That Cotek at 48V is only 91%. Is that extra 2% worth all the headache?

Cost: You can get 8 fortune 100ah lifepo4 cells for $900 which will give you 200AH at 12.8v which is 2.56kWh. Of go if you are dead set on 48V they sell 60ah modules. If you buy 15 of them for $1290 and that'll give you 60AH at 48V which is 2.88kWh.

AC Water Heat: This is where I see your system really falling short. 1400W induction or electric kettle shouldn't be a problem as you probably only use them for 2-5 minutes at a time, but a 1400W water heater can take 40-50 minutes to heat up the water in a 4 gallon tank. That's going to drain your battery pack quickly and frequently depending on often you use it. If this is for a shower, 4 gallons doesn't go as far as you think. If you are thinking of Diesel, you should look into the unit I have which is a Webasto Dual Top. It's a diesel hot water/forced air unit in one. I'm sure Espar has a similar unit. Or consider an aux tank for diesel like my van. It's a gas engine, but aux tank for the dual top. It's not "single source" but it's easier to find than propane and it's CRAZY how efficient they are.

Battery Chemistry/safety: Lifepo4's 3.2v resting voltage is for sure an added bonus for 4 in series coming to 12.8v, but the main reason why people are sticking with lifepo4 in rvs/vans is because of the safety and cycle life. Sure with a proper BMS you can make sure the battery operates in a normal range, but what happens if there is a manufacturing defect or you are in a car accident and the battery gets damaged? Electric cars are much different than camper van batteries as their BMS is MUCH more sophisticated and has been designed to address everything you can imagine can go wrong with the battery. Cheap Chinese BMS's for $30 on AliExpress don't NCR 18650s can catch fire. The worst thing that can happen with lifepo4 is it will vent, but it won't explode.

Please don't misunderstand my post. I'm not knocking your idea as I also have a propane-less van. I just think the time and energy you're going have to go through to build a 48V system is going to take a lot. It can be done, but I think it's going to be easier long run to simply go 12V with lifepo4 cells. Going 48V the way you suggested isn't going to give you any gains other than a tiny blimp in inverter efficiency. That 2 percent accounts for 55.6wh. In my eyes, I don't think it's really worth it.
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Old 12-19-2017, 02:49 AM   #8
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Originally Posted by kite_rider View Post
...
I can't think of a single electric car that is using IFR batteries. These cars are moving around *much* bigger batteries that are far more exposed than the proposed RV battery...???
The battery packs in all current Tesla vehicles are made up of a large quantity of the smaller 18650 cells just as you propose.
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Old 12-19-2017, 01:20 PM   #9
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Many of those home-built liCo battery packs cause fires. That is why we use LiFePo such as CALB.
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Old 12-20-2017, 06:25 AM   #10
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Thanks all for the feedback.

Lot's of good points see my feedback on each of these;

Quote:
Pack Assembly: If you plan on 280 cells, you'd be looking at a 14S20P config. I wouldn't bother making 4 different batteries. Just assemble as one large battery as that will make your BMS easier to manage. But be careful with the cells you selected as if they are only rated for 5amps, your max draw is going to be 5 amps X 20 = 100amps. You are still fine as your max amps at 48V with that 3500w inverter is going to be 80 amps but you are at the top end of that spec.
I would build the 4 smaller 14S5P batteries and put them in parallel for the following reasons;
1. The leads on my spot welder are not long enough to do 20 cells in parallel.
2. There are not many BMS devices that can handle this much current (at least ones that I'm familiar with).
3. If a cell goes bad, the whole battery needs to be worked on rather than a smaller module.
4. For the 'down and dirty' charging approach I could use off the shelf chargers. It would be hard to find a bulk charger that would charge this in any reasonable time.
5. Adding more stored power or reducing power is easily done by adding or removing grouped battery modules.

Quote:
Time: Assembling a 280 cell battery is going to take a lot of time and if you mess up the soldering of your cells, it's going to bring down the capacity of the entire pack.
Agreed. Bug again, diagnosing an issue would be easier if the batteries are grouped in 14P5S modules and then wired together in parallel via XT90 connectors.

Quote:
Cycle Life: NCR cells are only rated to around 500 cycles at the rate you are talking about draining them 20% compared to lifepo4 at around 3000.
Where are you getting the 500 cycle number? Well built cells (like the LG and Panasonic cells) are generally considered to last thousands of cycles. In any case, I would expect the lifepo4 batteries to have a similar cycle life if they were also quality cells.

Quote:
12V vs 48V: As you've mentioned, you are going to have a very hard time charging. Going from DC to AC then back to DC you're losing a lot of efficiency. Plus making your setup very difficult. Now inverting 48V DC to 110V AC is much more efficient IF YOU USE GOOD QUALITY PARTS! I'm not knocking the cotek as they are cheap but still good, but a magnum inverter at 12V is about 89% efficient. That Cotek at 48V is only 91%. Is that extra 2% worth all the headache?
A quick search for the12V 3KW Magnum inverter shows that it is priced at over $2,000 vs about half that for the 48V Cotek. Plus, the 48V Cotek smaller, lighter, requires much smaller gauge wiring and is more efficient. I'm not trying to push one brand over the other; I would say the same about the advantages of a 48V Magnum inverter. Really, the only headache would be configuring a voltage regulator to output 58V. Everything else is actually much less of a headache.

Quote:
Cost: You can get 8 fortune 100ah lifepo4 cells for $900 which will give you 200AH at 12.8v which is 2.56kWh. Of go if you are dead set on 48V they sell 60ah modules. If you buy 15 of them for $1290 and that'll give you 60AH at 48V which is 2.88kWh.
Good info on the fortune batteries. I don't have any experience with them. Is this what Hymer is using on it's EcoTrek battery? If I were to go with a 12V system and just use a standard alternator for charging this would be the way to go. Note that per my original discussion, you wouldn't have 2.56kWh of 'usable power' assuming you only ran 80% of it's capacity. Rather, it would about 2kWh compared to the similarly priced NCR solution with 2.78kWh.

Quote:
AC Water Heat: This is where I see your system really falling short. 1400W induction or electric kettle shouldn't be a problem as you probably only use them for 2-5 minutes at a time, but a 1400W water heater can take 40-50 minutes to heat up the water in a 4 gallon tank. That's going to drain your battery pack quickly and frequently depending on often you use it. If this is for a shower, 4 gallons doesn't go as far as you think. If you are thinking of Diesel, you should look into the unit I have which is a Webasto Dual Top. It's a diesel hot water/forced air unit in one. I'm sure Espar has a similar unit. Or consider an aux tank for diesel like my van. It's a gas engine, but aux tank for the dual top. It's not "single source" but it's easier to find than propane and it's CRAZY how efficient they are.
I share your skepticism about heating water with electricity. However, I met a guy in a converted Ford Transit at Descend on Bend who was using one of these Bosch heaters and he swore by it. By his account, the water would usually heat up while he was driving. He only had AGM batteries (not a lot either) and claimed that the unit was so well insulated that he didn't burn much power maintaining it. He wasn't taking long showers since he only had about 15 gallons in his freshwater tank to begin with. I'd love to hear from anyone who was actually using one of these to get some more feedback.

The webasto dual top is sweet, but expensive. I also love the Truma products and sometimes I think I'm the only person out here with the Alde boiler. It's water tank is really small, but it's scalding hot and seems last a very long time when I take showers. Note, I don't just leave the water running full blast since I'm almost always boondocking from a limited fresh water tank. Anyway, I may have the prices all wrong - but thought the dual top is over $2k installed where the Espar space heater is less than $1K installed. So that $1K extra for hot water could be used for the Bosch heater and a bigger battery (which in turn can be used for other things beyond water, like A/C). At least that was my thinking. Plus, I'm under the impression that a DIY person can't even buy the Truma or the Alde systems (not really relevant since they run on propane).

Quote:
Please don't misunderstand my post. .
Not at all! Appreciate the feedback. Ideally, I'd like to learn and consider as much as I can *before* I start building...
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Old 12-20-2017, 01:39 PM   #11
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See my replies in red:

I would build the 4 smaller 14S5P batteries and put them in parallel for the following reasons;
1. The leads on my spot welder are not long enough to do 20 cells in parallel.
Well that should make assembly much easier.
2. There are not many BMS devices that can handle this much current (at least ones that I'm familiar with).
Ah, if you are going to push your current through the BMS then yes, you are limited. Most larger battery BMS units us a shunt and external relays for the load and charge current as to not limit the current.
3. If a cell goes bad, the whole battery needs to be worked on rather than a smaller module.
Very true.
4. For the 'down and dirty' charging approach I could use off the shelf chargers. It would be hard to find a bulk charger that would charge this in any reasonable time.
True again but if they are going to be parallel anyway, you could still use one higher amp charger instead of dealing with 4 chargers.
5. Adding more stored power or reducing power is easily done by adding or removing grouped battery modules.
True again.

Agreed. Bug again, diagnosing an issue would be easier if the batteries are grouped in 14P5S modules and then wired together in parallel via XT90 connectors.

Also true.

Where are you getting the 500 cycle number? Well built cells (like the LG and Panasonic cells) are generally considered to last thousands of cycles. In any case, I would expect the lifepo4 batteries to have a similar cycle life if they were also quality cells.

Straight from Panasonic. Cycle life isn't 500 and the battery is dead, it's 500 and you've lost a large chunk of capacity. In your case you've lost about 1/3 of your capacity. The LG is even worse:



http://keeppower.com.ua/download/201...650_F1L_v1.pdf

Compared to lifepo4, you're still losing capacity but at a much more acceptable rate over many more cycles. You'll lose about 1/10th the capacity over 1500 cycles:



A quick search for the12V 3KW Magnum inverter shows that it is priced at over $2,000 vs about half that for the 48V Cotek. Plus, the 48V Cotek smaller, lighter, requires much smaller gauge wiring and is more efficient. I'm not trying to push one brand over the other; I would say the same about the advantages of a 48V Magnum inverter. Really, the only headache would be configuring a voltage regulator to output 58V. Everything else is actually much less of a headache.

Right, but you don't have to buy magnum. Even the Cotek 12V inverter is 88% efficent.

Good info on the fortune batteries. I don't have any experience with them. Is this what Hymer is using on it's EcoTrek battery? If I were to go with a 12V system and just use a standard alternator for charging this would be the way to go. Note that per my original discussion, you wouldn't have 2.56kWh of 'usable power' assuming you only ran 80% of it's capacity. Rather, it would about 2kWh compared to the similarly priced NCR solution with 2.78kWh.

I believe roadtrek at one time used GBS lifepo4 cells, but that my have changed.

I share your skepticism about heating water with electricity. However, I met a guy in a converted Ford Transit at Descend on Bend who was using one of these Bosch heaters and he swore by it. By his account, the water would usually heat up while he was driving. He only had AGM batteries (not a lot either) and claimed that the unit was so well insulated that he didn't burn much power maintaining it. He wasn't taking long showers since he only had about 15 gallons in his freshwater tank to begin with. I'd love to hear from anyone who was actually using one of these to get some more feedback.

Sadly I have no experience with it so I can't say. However if it works as well as that guy says, that might not be a bad setup. I've just heard a lot about electric water heaters taking too long to heat up the water which ends up taking it's toll on your batteries (both in capacity when you need it and adding more cycles as you are constantly cycling them.

The webasto dual top is sweet, but expensive. I also love the Truma products and sometimes I think I'm the only person out here with the Alde boiler. It's water tank is really small, but it's scalding hot and seems last a very long time when I take showers. Note, I don't just leave the water running full blast since I'm almost always boondocking from a limited fresh water tank. Anyway, I may have the prices all wrong - but thought the dual top is over $2k installed where the Espar space heater is less than $1K installed. So that $1K extra for hot water could be used for the Bosch heater and a bigger battery (which in turn can be used for other things beyond water, like A/C). At least that was my thinking. Plus, I'm under the impression that a DIY person can't even buy the Truma or the Alde systems (not really relevant since they run on propane).

Yea, the dual top is pricey but it works well and it's one of the few you can buy that you can install yourself. I was lucky that when I bought my van, the previous owner had already installed it. If it were up to me, I'd just go with forced hot air and no water heater. If I want hot water, I'd just use a small electric kettle to boil water.

Truma does make a diesel version of their combi, but they don't sell it in North American and you can't buy it yourself.


Not at all! Appreciate the feedback. Ideally, I'd like to learn and consider as much as I can *before* I start building...

Any time. I'd love to follow along as you build. I really like off grid systems and having them inside a van is even better. I may sound like I'm coming off against your 18650 plan, but truth be told I've got a 36v 18650 pack I put together for a 1500W escooter. For that it's great. But for a large storage solution in a van, I'd lean towards lifepo4 12v. You won't need your second aux battery to worry about. But whatever you end up doing,
please post in here or a new thread so I can follow along.
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Old 12-20-2017, 02:36 PM   #12
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... I wouldn't bother making 4 different batteries. Just assemble as one large battery as that will make your BMS easier to manage...



Are you serious?


Do you know why a BMS is required for Li batteries???
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Old 12-20-2017, 03:07 PM   #13
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Please look carefully about how much effort (e.g.) Tesla goes to mechanically isolate and armor relatively small numbers of cells for safety purposes.
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Old 12-20-2017, 03:14 PM   #14
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Originally Posted by BBQ View Post
Are you serious?


Do you know why a BMS is required for Li batteries???
Yes, to monitor the voltage for the cell group. In a 14s5p the BMS is going to monitor the 14 cell groups where each group has 5 cells in parallel. Those cells in parallel will balance themselves but each group needs to be monitored as there is no way to balance in series without a BMS. Having a 14s20p is basically the same thing just with more cell groups. Tesla uses the same strategy as it's too expensive to monitor each individual cell.

How do you think a large 100ah 12v battery is put together in any type of drop in battery like a battleborn or stark power battery? I'd be willing to be they use 2.5ah 26650 lifepo4 cells in a in a 4s40P config.
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Old 12-20-2017, 03:29 PM   #15
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Yes, to monitor the voltage for the cell group. In a 14s5p the BMS is going to monitor the 14 cell groups where each group has 5 cells in parallel. Those cells in parallel will balance themselves but each group needs to be monitored as there is no way to balance in series without a BMS. Having a 14s20p is basically the same thing just with more cell groups. Tesla uses the same strategy as it's too expensive to monitor each individual cell.

How do you think a large 100ah 12v battery is put together in any type of drop in battery like a battleborn or stark power battery? I'd be willing to be they use 2.5ah 26650 lifepo4 cells in a in a 4s40P config.

No, my comment is directed at something else. Please see my quote.
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Old 12-20-2017, 03:47 PM   #16
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No, my comment is directed at something else. Please see my quote.
Ah, I think I misunderstood what you meant. With four different 14s5p batteries, he'll 4 different BMS units. If you make one large 14s20p battery, you'd only need one BMS.
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