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bag-o-hammers asked

adding a multiplus 24/3000/70 and 24v 18650 battery bank to my 12v system

through a chain of events as payment for a debt I have acquired a MultiPlus 24/3000/70-50 and a 2.1kw Battery bank of 18650 cells. my 5th wheel trailer has a 12v system and a 2.8kw battery bank of A123 nano-phosphate cells. with no charger or inverter. I thought why not use both battery banks and mutiplus so I purchased an Orion tr smart 24/12 dc to dc charger, smart battery protect 12/24-220 , battery protect BP 12/24-100 my thought was to have the Multiplus charge the 24v bank and use it to provide AC when boondocking and when needed have the 24v bank charge the 12v bank.

secondly ... I also have 800watts of solar and a Victron 24/12 - 30 mppt smart controller I would like to install. my thinking there was to use 24v

does anyone have an opinion on this ? or is there a better solution? I have read several posts here that touch on nearly similar questions but were not definitive

thank you

john

orion-tr smart
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2 Answers
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JohnC answered ·

Hi @bag-o-hammers

What you propose will work. I've a similar setup with 48V & 12V Pb batts. Given the 48V is my inverter feed (main system), I provide it pv and 'shore' charge as priority, and treat the 12V system as an 'addon', but it's still important to me for 12V loads.

I charge the 12V with an older 20A Orion (not the newer Smart model) set for 13.5V straight, and controlled (on/off) by the V of the 48 bank with an Assistant in my Multi. So it gets charged whenever 54V is reached (which Pb's won't hold if not under charge).

I didn't bother with BP's as I think I have that need covered, but I do run a GX box, which I consider essential for a serious system. A recent addition of a Smartshunt on the 48 now shows me the DC load of the Orion as well, a coarse calculation of 'missing' current, but enough to show me the Orion charge level generally.

You may have challenges setting up Li systems with bms's or whatever, but for me this idea works well. I've fiddled with other ways of doing this over the last ~3 years, but this is my choice.



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bag-o-hammers avatar image bag-o-hammers commented ·

where I am at now ,,,

I have the multi 24 dc out connected to the 24 battery and since nothing in original RV is 24v this combination is isolated on the DC side. The 12v bank is connected to the RV distribution panel so it powers everything and isolated.

In the beginning, I used an ac to dc charger hooked to the multi 24's inverter. the charger was originally for lead-acid which kind of works with the lithium iron phosphate but the charger does not allow manual config, so I constantly have to deal with the absorption and float charging which is preset and unchangeable.

I have separated the slide, landing gear, and generator start onto a lead-acid marine deep-cycle battery and will use the ac to dc charger for that system.

these 3 systems are only connected by Earth Ground to the frame.

I have not yet installed the solar and wind turbine I wanted to have all issues solved before adding yet another complication.

is there a way to install the Orion which shares a ground between the 24v and 12v? I figured I should have bought the isolated version

if it is possible to use what I got it looks like there are 3 choices on where to hook the 12v ground.

1) to the negative on 24v battery

2) to the negative on the multiplus 24v

3) or connect both batteries negatives to the 12v negative busbar or frame.

I am not remembering my circuit design class after 45 years but it all seems wrong and will kill batteries.

if someone could point me in the right direction

thanks

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JohnC avatar image JohnC ♦ bag-o-hammers commented ·

@bag-o-hammers

I wouldn't get too excited about your negative connections.

In your mobile situation you're not really 'grounding', just using an 'earth return' via your frame. In a marine environment you wouldn't do that as it has serious corrosion implications. Mariners run two wires rather than one, and will only 'ground' in one place (if at all). As do many plasticky modern cars.

If your negative bus is convenient, just use that. Shouldn't affect your batteries adversely..



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bag-o-hammers avatar image bag-o-hammers JohnC ♦ commented ·

Thank you John it is working as intended. I really like the Victron products I cleaned up the circuit removing the redundant common cables. I appreciate the nudge, its what the manual said to do but I was hesitant. The dc to dc charger brings the 180ah pack from 11.5v to 13.2v in about 1 hr these nanophosphate A123 cells have super low internal resistance. ill take a break, letting this setup cycle for awhile and tackle the solar and wind next week. regards john

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bag-o-hammers answered ·

hello, @JohnC I have the system running now for 5 days or so and I have been thinking about it and I believe I am going to change from having the Orion manage the charging. the on-off method seems more like what I would prefer. if I understand correctly you have an assistant that closes a relay that the wires run to the on/off connection on the Orion. when the multi charges the 48v bank to 54v it closes the relay which starts the Orion. I noticed that I too can set it to 13.5 strait. so the Orion pulls from the 48v bank. do you then have the assistant open the relay when your 48v falls below a set point turning the Orion off? this seems like a more elegant solution. doing it this way will give a clean charge/discharge cycle not having to deal with the absorption and float with which lithium doesn't fair too well and with the low resistance of my 12v bank, it doesn't take much of a push to get to full charge. it takes about 45min to a hour to go from 11v to 13.2 with 2 to 3 amps, thank you for your help. john

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JohnC avatar image JohnC ♦ commented ·

@bag-o-hammers

Yes, I actually have the Orion cut in at 54.5V and out at 54V to try to give it a stable run, and that seems to work ok. It's also below the V required to have my Smartshunt auto-sync, so any switching won't interfere with that.

There may be little things like that to consider with your Li's, but all you can do is try. Sure it's elegant enough, and reliable to the point I forget about it.

But you understand, just get in and play.. :)

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