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Old 11-25-2020, 10:31 PM   #21
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Magic smoke?


You might be OK for damage if you hooked up the 12v controller in the middle of the 24v string of panels, but I can't understand why you would do that.


I wonder if they are using an MPPT solar charger like a 24 to 12v converter to charge the the two front batteries at 12v from either the solar or the shore charger or 24v bank. There may be some switching going on between the chargers depending on shore power, engine running, only solar times. Roadtrek did so many silly a$$ things with the etrek design, I would not rule anything out.
if you have solar panel array that puts out 30+ volts to charge the 24 volt bank through a 24 volt MPPT controller couldn’t you connect a 12 volt MPPT controller in parallel to the same panels assuming it can handle 30+ volts input?

I may have my head where the sun don’t shine but this wouldn’t be the first time...
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Old 11-25-2020, 11:46 PM   #22
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if you have solar panel array that puts out 30+ volts to charge the 24 volt bank through a 24 volt MPPT controller couldn’t you connect a 12 volt MPPT controller in parallel to the same panels assuming it can handle 30+ volts input?

I may have my head where the sun don’t shine but this wouldn’t be the first time...

I am certainly not sure either way. I don't think they would blow up, but I don't know how they would control. For sure they would have to be the same brand, model, rev level, etc with only the output changed. Open circuit is about 42.5v or so on a 24v modern panel and maximum power point like 35.4v. Both controllers are going to be trying to control the input voltage to run maximum output power so basically targeting the MPPT point of 35.4v for the input or if they aren't putting out enough whatever point will give the most power. If they did that and were identical units set differently, they might do fine as long as the different output voltage didn't do something different in the units because the 12v unit would put out twice the amps on the output side if they evenly split the input.


It is very interesting idea for sure, and if you throw the 24v charging or battery input on it, it would get even more "interesting", I think.


Roadtrek did run some multi controller setups that were probably parallel, but may have been wired with separate and the same amount of panels on the input. I have no idea if they had a common input.
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Old 11-26-2020, 05:40 PM   #23
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Wow. I just spent the past 2 days out in the camper and I come back and you guys have it all figured out!

Here is some further info:

1. Yes, this seems to be a twin of the Roadtrek Demo Van that was described in these two posts:
https://www.classbforum.com/forums/f...a-c-10973.html
https://www.classbforum.com/forums/f...tml#post116514
Maybe it is even the same van, if the original poster did not actually purchase it?

2. The 12V system, powered off the the two under-hood 6V batteries, does run the refrigerator, DC outlets, the Alde circulator, and other misc. DC appliances.

3. The 24V system runs a ProAir split undermount AC. The Eight 6V batteries under the chassis provide the power.

4. The two battery banks are connected by a Cooper Bussmann Battery Equalizer. I believe that this equalizer could be used as a converter, if I were to ditch the 12V battery bank. I can't seem to find an exact match on the model, but I will keep looking.
http://www.cooperindustries.com/cont...ST_180156a.pdf

5. The ~600 W of solar feed into two separate MPPT controllers. One is at 12V and the other is at 24V and the 12V seems to enter float mode a little earlier than the 24V bank. This is likely because there are only two batteries in that bank and also those batteries are brand new (dealer replaced them after they were found to be unable to hold a charge).

6. I haven't verified this yet, but it is possible that the 12V bank is recharged off the engine alternator and the 24V bank is charged off of the under-hood generator. I will check that out the next time I am under the hood.

*****
So it is beginning to sound like I should plan on swapping the whole system over to 24V to both simplify the electrical system and eliminate the long cable run to the under-hood batteries. I assume that they died earlier than the rest of the batteries because they get a lot of abuse running the refrigerator and being under the hood. I will start a new thread about the conversion process.

In the meantime, it also sounds like I could set up a battery monitor system using a Blue Sea State-of-charge Monitor. I could easily set that up on the 24V positive lead, just where it connects to the battery equalizer. That would enable me to monitor that set of batteries and once I set up the new 24V-only system, it would be monitoring everything.

Thanks so much for all of your insight!
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Old 11-26-2020, 06:54 PM   #24
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Wow. I just spent the past 2 days out in the camper and I come back and you guys have it all figured out!

Here is some further info:

1. Yes, this seems to be a twin of the Roadtrek Demo Van that was described in these two posts:
https://www.classbforum.com/forums/f...a-c-10973.html
https://www.classbforum.com/forums/f...tml#post116514
Maybe it is even the same van, if the original poster did not actually purchase it?

2. The 12V system, powered off the the two under-hood 6V batteries, does run the refrigerator, DC outlets, the Alde circulator, and other misc. DC appliances.

3. The 24V system runs a ProAir split undermount AC. The Eight 6V batteries under the chassis provide the power.

4. The two battery banks are connected by a Cooper Bussmann Battery Equalizer. I believe that this equalizer could be used as a converter, if I were to ditch the 12V battery bank. I can't seem to find an exact match on the model, but I will keep looking.
http://www.cooperindustries.com/cont...ST_180156a.pdf

5. The ~600 W of solar feed into two separate MPPT controllers. One is at 12V and the other is at 24V and the 12V seems to enter float mode a little earlier than the 24V bank. This is likely because there are only two batteries in that bank and also those batteries are brand new (dealer replaced them after they were found to be unable to hold a charge).

6. I haven't verified this yet, but it is possible that the 12V bank is recharged off the engine alternator and the 24V bank is charged off of the under-hood generator. I will check that out the next time I am under the hood.

*****
So it is beginning to sound like I should plan on swapping the whole system over to 24V to both simplify the electrical system and eliminate the long cable run to the under-hood batteries. I assume that they died earlier than the rest of the batteries because they get a lot of abuse running the refrigerator and being under the hood. I will start a new thread about the conversion process.

In the meantime, it also sounds like I could set up a battery monitor system using a Blue Sea State-of-charge Monitor. I could easily set that up on the 24V positive lead, just where it connects to the battery equalizer. That would enable me to monitor that set of batteries and once I set up the new 24V-only system, it would be monitoring everything.

Thanks so much for all of your insight!
Sounds like you have a good plan going forward.

If you do have to get a different 24 to 12 converter, you probably would want to keep the balancer also, as Marko suggested to improve battery balance and life of the 8 batteries.

You would also be able to rewire the battery connection jumpers at the same time if they are uneven lengths to improve balance.

If the solar controllers are settable for output, and identical otherwise, you probably will be able to use both as one may not handle 600 watts. If you have to go to a bigger single unit, you may want to consider getting a Blue Sky with the Pro remote as it will give very accurate charging and it also includes a battery monitor so you wouldn't need a separate one. With the updated system, you should be able to get to a one cable ground so any monitor with a shunt should work.

Do the controllers currently run parallel on the full 600 watts of panels or do the each have their own panels?

I think when you are done, you will have a very nice setup.
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Old 11-27-2020, 02:57 PM   #25
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The MPPT solar controllers are Renogy 40A models, like those shown here:
https://www.lastmilesolar.com/produc...ge-controller/
According to the technical specifications that I found elsewhere, the controller can handle a maximum input of 400W at 12V and 800W at 24V. One controller is at 24V and the other is at 12V and they are obviously charging two different banks of batteries.

Now the panels are of at least two types. The attached picture shows the stock 240 watt panel. Under the original Adventurous configuration, that was 24V. The back 4 panels, if they were 90W each, would bring the total to 600W, which is what I have read somewhere else. Assuming that these are 12V panels, then I would have to rewire them to produce 24V.

At that point, the one charge controller would handle the whole load, but I think that you are right that it would make sense to upgrade the charge controller to a smarter model that would serve as a battery monitor, like the Blue Sky.
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Old 11-27-2020, 05:23 PM   #26
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The MPPT solar controllers are Renogy 40A models, like those shown here:
https://www.lastmilesolar.com/produc...ge-controller/
According to the technical specifications that I found elsewhere, the controller can handle a maximum input of 400W at 12V and 800W at 24V. One controller is at 24V and the other is at 12V and they are obviously charging two different banks of batteries.

Now the panels are of at least two types. The attached picture shows the stock 240 watt panel. Under the original Adventurous configuration, that was 24V. The back 4 panels, if they were 90W each, would bring the total to 600W, which is what I have read somewhere else. Assuming that these are 12V panels, then I would have to rewire them to produce 24V.

At that point, the one charge controller would handle the whole load, but I think that you are right that it would make sense to upgrade the charge controller to a smarter model that would serve as a battery monitor, like the Blue Sky.

Good information, thanks.


The link shows the 40A with even higher ratings for total watts of 500/1000, even.


The appear to autorecognize the battery voltage and set themselves so they are not set any differently for the two sides.


Max solar input voltage is 100v so all the panels could be anywhere in that range.


The first, larger panel is probably the standard 24v one which would have open circuit at around 43v.


The last 4 are probable 12v panels of around 100+/- some, whats so you are likely correct on that. They could be wired for 12,24,36, or even 48v and would work with that controller with the 100v input would still be met.


With an MPPT the input does not need to match the output voltage.


I think it probably they are currently wired for 24v with two series panel pairs in parallel so would be good to go, but need to check for certain.


The one weakness of the Blue Sky stuff is their lower than many max voltage ratings, but they can handle 24v panels, so that would work. Probably a 3024i with Pro Remote and shunt.
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Old 11-29-2020, 09:15 PM   #27
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Interesting configuration. Are the 12v batteries in front connected to a midpoint 12v tap in the 24v strings in back similar to the standard 8 AGM model with the balancer equalizing current across the back batteries?

Is there a Smart Solenoid connection between the front 12v batteries and the chassis battery to pull in charging from the chassis alternator?

What 110v inverter is installed? Does this only pull current from the back 8 AGMs or does the balancer cause current to be drawn from the front 12v system? Does the refrigerator switch to 110v if available and off of the 12v system in front?

Might the 12v system in front possibly buffer the 24v strings from repeated shallow cycling and wear and perhaps allow longer life of the 24v string at the expense of more frequently replacing the 12v pair?

Do any of the charging sources have a proper temperature adjusted charging profile for the AGMs? Do either of the solar controllers provide useful historical information?

Are the two additional AGMs in the back tucked behind the passenger side rear wheel well? Have the wiring lengths for the rear 8 AGMs all been synchronized now that the batteries are closely clustered?
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Old 12-15-2020, 12:46 PM   #28
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Here is the latest update. It took awhile to figure out all of the info that you were asking about, and I'm not certain about all of it:

1. What are the solar panels outputs?
Your educated guess of 43v and was correct for the one big panel. That panel is connected to the solar controller with a 24v output. The other four panels are outputting 36v.

2. Are the 12v batteries in front connected to a midpoint 12v tap in the 24v strings in back similar to the standard 8 AGM model with the balancer equalizing current across the back batteries?
I don't think so. I wasn't able to figure out the complete wiring diagram because it is so hard to access the batteries under the chassis. However, it looks to me like the 12v and 24v systems are connected to each other through the Balancer.

3. Is there a Smart Solenoid connection between the front 12v batteries and the chassis battery to pull in charging from the chassis alternator?
Yes. There are two Battery Separators that I can find. One is under the hood and looks like it connects to the 12v front batteries and the engine battery. The other is near the battery separator and connects the 12v and 24v systems.

4. What 110v inverter is installed? Does this only pull current from the back 8 AGMs or does the balancer cause current to be drawn from the front 12v system? Does the refrigerator switch to 110v if available and off of the 12v system in front?
The inverter is a 5000W Sine Wave Combined Inverter and Charger. It is definitely connected to the 24v system and I suspect that as it draws those down the Balancer would pull from the 12v batteries. Yes, the refrigerator is 12v/110v and is supposed to switch to 110 when its available (although that, apparently, is only when the inverter is on even when connected to shore power).

5. Might the 12v system in front possibly buffer the 24v strings from repeated shallow cycling and wear and perhaps allow longer life of the 24v string at the expense of more frequently replacing the 12v pair?
I think that is so, whether by design or not. I have been told that the 24v batteries directly power the under-chassis mounted AC, but I suspect that is actually because the Inverter needs to be on for the AC and it will then be drawing through the Inverter. I am considering wiring the refrigerator directly to the 24v tap to decrease the short-cycling that it does on 12v power, but I haven't committed to that yet.

6. Do any of the charging sources have a proper temperature adjusted charging profile for the AGMs? Do either of the solar controllers provide useful historical information?
Maybe on the temperature adjusted charging. The Inverter (shore power) does not. The Alternator does not (as far as I can tell). The Solar Controllers are supposed to, according to something that I read somewhere. But they don't have any external temperature probe, so they would have to do it at their own internal temperature. So I guess that is probably a no, as well.
None of the electrical system is "smart". This whole discovery odyssey started with my attempt to install a smart battery monitoring system.

7. Are the two additional AGMs in the back tucked behind the passenger side rear wheel well? Have the wiring lengths for the rear 8 AGMs all been synchronized now that the batteries are closely clustered?
Yes, that is exactly where they are. As far as I can tell (and I got a pretty good look), no attempts were made to equalize the wiring lengths.

So to summarize where I am now. I think that I will install at least one battery monitor on the 24v bank to get a feeling for how that battery bank is being used under real-world conditions. I will also see how long the two new batteries under the hood last (the 12v bank). If those die early then it will be good motivation to switch the whole thing over to the 24v bank only. A second alternative to consider will be to eliminate the under-hood batteries but switch the two batteries behind the rear tire to run the 12v system. Once I get a better idea about how the 24v bank is actually used/recharged I will be able to see what might be the better option.

Thanks again for all your help!
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Old 12-17-2020, 11:44 AM   #29
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Thanks for all of the detail you posted! That the two front batteries die early seems to be an accepted fact of life. Why they die early is probably open for investigation. Many people blame the heat in the engine compartment.

I have the 8 AGM ETrek and installed two Victron 712 battery monitors, one on each ground. The aux input on each battery monitor was used for a battery temperature sensor. I found that under normal driving conditions the two batteries in front were running cooler than the ones in the back. This was reversed in stop and go in city driving.

So the question is open on the two front batteries; is it temperature, are they being cycled out, or are they more frequently left in a partially discharged state and lose capacity as a result. Without a battery monitor my money would be on the front batteries being left frequently in a partially discharged state.

When people eliminate the two front batteries they often sacrifice some functionality. This includes charging from the chassis alternator and the "Smart Solenoid" connection to have the house batteries back up and provide emergency cranking assist to the chassis battery. These may or may not be important to you.

Sounds like the AC is an 110v system if the inverter needs to be on. Sounds like the balancer is installed as a DC to DC charger for the two front batteries vs balancing the charge across the back eight?

It is an interesting puzzle as to how to progress the different components by adding smartly and not losing functionality. My priorities are having good battery temperature and status information and then using this information to have adjusted absorption and float charging. I plan to replace my solar controller with a Victron model which will use the battery monitor temperature readings. These components seem to be the farthest along in actually being designed to work together and provide useful information. This will also tell me if I actually am capturing enough solar to adequately provide these two charging states.

I envy that you have a fully contained 24v system in the back. This is one of the configuration challenges I still need to address with just the 6 battery back bay.
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Old 12-17-2020, 06:57 PM   #30
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There is no real advantage to having the 12V house batteries set up in series for 24 volts. They are not feeding 24 volts to anything downstream. A MPPT controller can accept 20 volts from a 12V nominal panel or 30 volts from a 24V nominal panel and feed 14 volts to the battery bank. Having the 12V batteries in series does not alter the time it take to recharge them.

I would wire the existing batteries in parallel if possible (some controllers cannot manage more than 3 batteries in a parallel configuration which may be why the unusual two batteries in serial was done.

Going forward, a lithium phosate battery can be discharged by 90% without damage and it can be recharged three times as fast with up to 100 amps charging than a FLAT or AGM battery.

There is also a considerable amount of weight that can be saved. 10 100AH AGM batteries that can only be discharged by 50% provide 500AH of capacity. A 100AH lithium phosate battery that weighs half as much can be discharged 90% and 5 of them would provide 450 AH of capacity for a total weight reduction of more than 450 pounds.
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