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Old 11-26-2021, 10:17 PM   #1
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Default DIY 280A Lifepo4 Lithium in 2019 Roadtrek

In my 2019 Roadtrek Simplicity my inverter/charger stopped working due to a shorted battery. I cant find the problem with the inverter so I decided to take the opportunity to change to Lithium. I bought 4 3.2v 280A cells and built up a 280A pack. I also bought a 150A BMS and a new 2000W sinewave inverter, 10A charger and AC switch. Everything hooked up and working. Then today I found a problem.

I decided to try out the voltstart function by running a 1500w heater, everything went fine until the voltstart started the engine. I forgot the under hood generator was 280A, the BMS is 150A I saw the charge at 180A and after a few minuets the BMS shut down, then after another minute it restarted. It seems the BMS is too small for the under hood generator. Has anybody had this problem? What did you do?
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Old 11-27-2021, 12:23 AM   #2
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I think the accepted wisdom is to never connect an alternator directly to a lithium battery. Putting a DC to DC charger in between solves the problem.
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Old 11-27-2021, 01:02 AM   #3
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There is a BMS between the Alternator and Battery.
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Old 11-27-2021, 01:15 AM   #4
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There is a BMS between the Alternator and Battery.

The BMS will turn on or off the charging, what you need to do is limit the charging current so you don't cook things like the batteries, BMS, and potentially the wiring. How big a cable do you have from the front to the batteries?


I think we are all assuming you have 290 amp hours of batteries not an amp rating. You would need to check with the battery manufacturer to find out what the maximum charge rate that they recommend it.


You are messing with currents that could easily cause a fire, so it may be time to study up a bit on how all the stuff needs to tie together and match.
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Old 11-27-2021, 02:46 AM   #5
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There is a BMS between the Alternator and Battery.
Not good enough. Booster explains it better than I could. The need for a DC to DC charger remains.
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Old 11-27-2021, 02:48 AM   #6
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Recommended > than 1C
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Old 11-27-2021, 02:52 AM   #7
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Recommended > than 1C

Cable size?
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Old 11-27-2021, 03:03 AM   #8
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Not good enough. Booster explains it better than I could. The need for a DC to DC charger remains.

If the 2nd alternator has a Balmar regulator on it, it could be set to turn down to 50% on one input with a switch or another that sets a % that may go a bit more. That would give about 120-140 amps, but not control voltage unless set at a fixed voltage output on the regulator.



If the cable is big enough to handle that much continuously, it would be more efficient than a B to B as the B to B inefficiency would not be there and we have heard that is about 20%. It would be like having a 120 amp B to B but without the cost or having to find a place for it.


As I said before, I think it would be of great benefit for the OP to read some of the many discussions on this forum that go over how all this stuff works together to give a good, consistent, and safe system.
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Old 11-27-2021, 03:17 AM   #9
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I have been reading everything I can find, You may be surprised at all the contrary information that's out there and in here. There are a lot of wrong "Experts". Or maybe I should say alternative facts.
Yes this 2nd alternator (UHG)is supposed to have a Balmar regulator, I have been researching that possibility all day. Right now I'm trying to find the location of it without going outside in 35 degree temp. Cable from the Alternator looks like 00, it gets smaller closer to the house battery. Maybe 4.
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Old 11-27-2021, 01:28 PM   #10
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I have been reading everything I can find, You may be surprised at all the contrary information that's out there and in here. There are a lot of wrong "Experts". Or maybe I should say alternative facts.
Yes this 2nd alternator (UHG)is supposed to have a Balmar regulator, I have been researching that possibility all day. Right now I'm trying to find the location of it without going outside in 35 degree temp. Cable from the Alternator looks like 00, it gets smaller closer to the house battery. Maybe 4.

I hear you on the contrary information, the internet is full of that kind of thing. In general, don't believe anything from a single source be it on this forum or elsewhere, is a good rule. Once you think you have found something that make sense to you (technical background, of course, aids in this evaluation but not essential) it is usually beneficial to go out and search for the details of that point. Technical articles are OK to use, but not a good as they used to be because a lot of manufacturers are writing them now, or having independent "experts" write them and can be very slanted. University level research and testing is often the best source if you can find it. Yep, it is very tedious and time consuming and often very high tech jargon. I think you find that on this forum, which kind of has reputation for being a good tech source in general, you will commonly asked to provide sources for the claims made and data to back them up. It isn't personal or meant to be dismissive, it is meant to filter out as much of the misinformation as possible. In many cases, questions can't be properly answered without a lot more information than is often given, and a poor recommendation if worse than none.


That said, lithium systems are wild west of power systems, with huge variations in what is considered necessary to make them work. Variations from the need for very complex systems to "drop em in and go" are very common. It is all because that is still being hashed out in the market, and the correct place is probably somewhere between the two ends. There are numerous people on this forum that have built their own systems, including some very sophisticated ones and some that are more basic. I am not one of them as we have a large AGM bank that is working very well, but I try to keep up just in case a change is ever needed, and it is also quite interesting. In general, most function OK but there is little information on long term life of the batteries yet as it all is so new and even at half rated life lithium can last a long time in a non full time camper.



All that said, your system does raise a bit of alarm. Hearing of a 180 amp, overcurrent component failure immediately is a concern for safety. Batteries capable of 290 amp charging and an alternator that can do that much, at least for a short time, but with a 180 amp BMS, indicate that the system hasn't been thoroughly matched. You may even have been lucky the BMS failed before the wiring overheated if it is #4 in places. 00 would be fine all the way, especially if you limit current some. For reference I like to use the Blue Sea Circuit Wizard Circuit Wizard - Blue Sea Systems to check wire sizes. It will give you free air ampicity, derated (in loom or such) ampicity, voltage drop. It is tuned to marine specs, so on the conservative side, so very safe recommendations.


You probably have the Balmar MC-614 regulator that is commonly used. Here is the manual for it. https://www.balmar.net/wp-content/up...ion-Manual.pdf. Modifying the output can be done with "belt load manager" setting down to 55% field current which may give more or less than 55% output but is a substantial turn down. You can also limit output by using an override switch on the alternator temp sensor to make it think it is in high temp turndown mode which is about 50%. Both of these settings reduce the field current in the alternator so don't measure and limit output to a setting of amps, so won't be exactly on the same % with output. Balmars can be a PITA to program with the little magnetic probe, especially if they are in a hard to get at place.


Getting the system matched up for charging currents and all the various settings should not be a huge deal, depending on what actual equipment you have for charging and how settable they are.


Have you looked at the potential issues of battery heating, cold shutoffs and recovery of cold shut downs for charging and storing to this point? If you ave 35* already, you are likely in a pretty cold area, so may be issues. Many of us here consider the BMS to be just the final backup safety and control device so often some other, settable things may be a good idea. Nearly would all now say no charging below freezing and many pad that by few degrees as it more of sliding scale and not a cutoff, so between 34* and 41* are pretty common. Storage temp minimums are still in dispute more, with best practices saying no storage below -4*F, others saying -20*F, some at -40*F, some no limit. The -4* is gaining more traction lately though so puts a lot of North America in need of heaters if stored outside and unheated.
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Old 11-27-2021, 08:17 PM   #11
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Thank you for the detailed answer. Im an engineer and the more I dig the more I learn. You are right about Lifepo4 being all over the place but most people get it to work. In my case putting a DIY in a MH is not that common. I have read of people doing it but few discuss charging except with solar. Which I also have.
Here is some more info on my system. The original battery is underneath the chassis at the back. The wiring starts out as 0 or 00 and at the batteries they made 2 runs in parallel with smaller wire and lots of fuses. I brought in the 0 gauge wire that was connected to the old battery to the new location of the new battery which I put in the inside box where the original Inverter/charger was.
In the fall winter I keep an electric heater in the MH which is a class B. I have a remote Temp monitor in the box I try to keep the Temp in the 40's. I have never winterized any MH in 20 years. Never had a problem. NE Alabama (another subject) I have found the Balmer manual yesterday and you are right its supposed to be a MC-614 I also found the programming instructions, IF it really has one, some of the same MH's came without them.
My 2nd idea is another BMS in parallel. That would cost around $100 and gets me to 300A. I have a AGM battery still installed that has been discussed could be put with the Lifepo4. I have tried that and it cuts the 280A charge time down significantly since its internal resistance is much higher. The charge starts at 280A and quickly drops to around 100A. I have read pros and cons. The charge discharge cycle is different but the charge will get me approx. 85 to 90% on the Lifepo4. I could also replace the 2nd Alternator (UHG) with a smaller 150A one, about $150. My first choice is to reprogram the Balmar as you suggested.
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Old 11-27-2021, 10:08 PM   #12
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Thank you for the detailed answer. Im an engineer and the more I dig the more I learn. You are right about Lifepo4 being all over the place but most people get it to work. In my case putting a DIY in a MH is not that common. I have read of people doing it but few discuss charging except with solar. Which I also have.
Here is some more info on my system. The original battery is underneath the chassis at the back. The wiring starts out as 0 or 00 and at the batteries they made 2 runs in parallel with smaller wire and lots of fuses. I brought in the 0 gauge wire that was connected to the old battery to the new location of the new battery which I put in the inside box where the original Inverter/charger was.
In the fall winter I keep an electric heater in the MH which is a class B. I have a remote Temp monitor in the box I try to keep the Temp in the 40's. I have never winterized any MH in 20 years. Never had a problem. NE Alabama (another subject) I have found the Balmer manual yesterday and you are right its supposed to be a MC-614 I also found the programming instructions, IF it really has one, some of the same MH's came without them.
My 2nd idea is another BMS in parallel. That would cost around $100 and gets me to 300A. I have a AGM battery still installed that has been discussed could be put with the Lifepo4. I have tried that and it cuts the 280A charge time down significantly since its internal resistance is much higher. The charge starts at 280A and quickly drops to around 100A. I have read pros and cons. The charge discharge cycle is different but the charge will get me approx. 85 to 90% on the Lifepo4. I could also replace the 2nd Alternator (UHG) with a smaller 150A one, about $150. My first choice is to reprogram the Balmar as you suggested.

Pretty much every lithium system here is in a motorhome!



I am afraid you lost me with the charge cycle being faster when you add an AGM to mix with the lithium. How they charge will depend a lot on the size of your charger and it's ability to hold charge voltage on both with all the load, which as you have seen can be quite high with the lithium. Very likely the charge voltage drops so the AGM charges slower than it would until the charger catches up. AGMs take a long time to charge to full, usually in the 8-10 hour range for a 50% discharge and it is only influenced a little by charger size. Finding a solution for the slow AGM charging without going to all lithium was the original premise that we looked at here on the forum. You would charge them both at the same time and when you run out of time you would shut off the charging and charge off the lithium, smaller battery. At the time lithium was very expensive so you could have a larger AGM bank and a small lithium to complete the charging on the AGM. It would be suitable for those with generators they use for recharging to reduce the generator run time. With lithium getting so inexpensive it really isn't all that useful anymore.


I would not consider replacing the alternator with a small one unless your system can't handle 1/2 of the output of the 280, because you can get that with a Balmar and also set if for constant voltage for the lithium charging. A 150 amp alternator will only do that 150 for 15 or 20 minutes in most cases and then it would get to hot and you would either have to shut it off or turn the output down to let it cool. Turning down what you have, even if you have to add a Balmar if it doesn't have one is much better, and a B to B would also be better than a smaller alternator. running an alternator on half power is very good for them if it is enough power for you and the alternator will last substantially longer in most cases.



Many folks here are charging lithium off of solar, although some don't think solar is even needed if you have an engine charger. This is probably true for large amounts of power use folks, but for smaller banks and moderate use, solar can allow quite a bit more offgrid time with running the engine. No mystery to it as long as the charging voltages match the other sources fairly well. For lithium, I think most users who have better controlled systems use fixed voltage charging as stages are pretty useless for lithium, but full charging cutoff is beneficial, by most accounts.



Be aware that all your charging sources should to be setup to shut off in a matter that doesn't destroy them if the BMS or other controls take the batteries off line for some reason. Solar and alternators are the most vulnerable, but most shore chargers not nearly as much. If you have solar panels in the sun and the battery reference voltage goes away, you can very large spikes in voltage that can damage the controller and other electronics in the van. Best to have the panels disconnect as that is where the extra voltage is coming from. With alternator you would want to disconnect the field, not just a main disconnect or the same unreferenced voltage happens. Using a B to B charger usually would isolate the alternator and protect it. Roadtrek used to put a small AGM in the system for just these reasons, I think, to not lose the battery reference voltage if the lithium batteries went offline or were shut off.



Someone on the forum who has done their own lithium system would probably be able to let you know if you can parallel two BMS modules on the same battery or if they would need to be split to two batteries, as I have no knowledge of that every being done.
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Old 11-27-2021, 11:56 PM   #13
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Ok, I'm posting on 2 forms, this one and the solar forum. Getting way different answers.
About the AGM, I noticed without the AGM hooked up the current stayed at 250-280A longer than when the AGM was hooked on. Im not stating what Im going to do I'm just stating what I could do to resolve the problem. Right now I think reprogramming the Balmer, if I have one is the cheapest and best solution, 2nd best is adding a second BMS 150A. in parallel if feasible, 3rd is changing out the 2nd alternator for a 150A one.
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Old 11-28-2021, 12:12 AM   #14
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Ok, I'm posting on 2 forms, this one and the solar forum. Getting way different answers.
About the AGM, I noticed without the AGM hooked up the current stayed at 250-280A longer than when the AGM was hooked on. Im not stating what Im going to do I'm just stating what I could do to resolve the problem. Right now I think reprogramming the Balmer, if I have one is the cheapest and best solution, 2nd best is adding a second BMS 150A. in parallel if feasible, 3rd is changing out the 2nd alternator for a 150A one.

What reason do they give for not charging lithium with solar?
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Old 11-28-2021, 12:23 AM   #15
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I have not seen any neg remarks, but I didn't look.
https://diysolarforum.com/
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Old 11-28-2021, 08:34 AM   #16
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I found this video by Will Prouse that talks about paralleling 2 BMS's but he doesn't talk about charging, only discharging, I am hoping that the charging would work the same.

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Old 11-30-2021, 12:50 AM   #17
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The more I read the more negative things I find on charging Lifepo4 with an alternator. My original problem was trying to charge a 12v 280A Lifepo4 battery and 150A BMS with a 2nd alternator that puts out 280Amps. Solutions so far.
DC to DC converter, High cost low amps.

Smaller alternator may burn it out by sourcing high current too long.

Paralling 2 150A BMS's People disagree on this, and same possible problem with the Alternator sourcing high current too long. Also I read that the BMS turning off the charge can damage the alternator.

Adding a Balmar Best solution, High cost.

New Potential solution Since the high current is for usually less than 5 minuets before it settles to 120A or less I could use a relay (starter solenoid) to short the B- and C- until the Battery voltage reaches 13.5V or some value that reduces the current below 150A.
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Old 11-30-2021, 02:00 AM   #18
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If after 5 minutes, you only charge at 120A anyway, then a 120A Sterlin B2B would be a simple solution. Not cheap though.
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Old 11-30-2021, 02:03 AM   #19
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600.00 Cost too much.
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Old 11-30-2021, 04:50 AM   #20
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The more I read the more negative things I find on charging Lifepo4 with an alternator. My original problem was trying to charge a 12v 280A Lifepo4 battery and 150A BMS with a 2nd alternator that puts out 280Amps. Solutions so far.
DC to DC converter, High cost low amps.

Smaller alternator may burn it out by sourcing high current too long.

Paralling 2 150A BMS's People disagree on this, and same possible problem with the Alternator sourcing high current too long. Also I read that the BMS turning off the charge can damage the alternator.

Adding a Balmar Best solution, High cost.

New Potential solution Since the high current is for usually less than 5 minuets before it settles to 120A or less I could use a relay (starter solenoid) to short the B- and C- until the Battery voltage reaches 13.5V or some value that reduces the current below 150A.
Balmar regulators are like $300. Probably worth it if you have an independent second alternator.


Another option for your list (just for completeness):
Use the alternator to power a 120VAC inverter. Use its output to power your shore-power charger.
Inefficient, but not completely crazy.
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