Battery Bank - wire for 12v, 24v, or 48v?

pianotuna wrote:
If you plan on a large inverter definitely jump to 48 volts. I'd pick Outback or Victron with a hybrid (load support) feature.

Mind me asking why? What's the benefit to the higher voltage?

Yes, I made all the adjustments to the Victron (Peukert, etc) based on the battery manufacturer's recommendations, but it's still not accurate. We're not talking a small discrepancy, more like the BMV shows 83% charge (with voltage at 13.2?) vs 98% on the BMS panel. And this after a full charge the day before - sitting in driveway hooked up to shore power.
Samlex gave me instructions on how to set up the inverter charger (3012) as a 2 stage charger to allow the batteries to trickle down (via parasitic draws) to 80% and then kick in charger to boost back up to 100% - this all based on the idea that it's not good to keep lithium batteries at 100% SOC for long periods of time. I surely have a setting wrong somewhere, just haven't had time to drill down into it.

Hi,

If you plan on a large inverter definitely jump to 48 volts. I'd pick Outback or Victron with a hybrid (load support) feature.

The existing converter may be used to provide for 12 volt needs. There are many dc to dc units as well.

phemens wrote:
I just did a battery revamp and added 4 lithium batteries, stayed with 12v setup due to pre-existing 12v inverter charger. Very happy with it, They don’t sweat high draw loads, but i’m finding that my Victron 702 is not an accurate indicator of charge. I think it calculates it based on amps out but doesn’t seem to jive with the readings I see on each of the batteries via their BMS panel. Some tweaking to do there. Agree that amps in and out will be the main indicator, but not sure yet how to accurately show that via the 702.

When I installed my BB batteries, they had a document of specific settings for the lithium batteries. Things like Peukert Effect and whatnot have to be adjusted for the BMV to calculate use properly.

phemens wrote:
I just did a battery revamp and added 4 lithium batteries, stayed with 12v setup due to pre-existing 12v inverter charger. Very happy with it, They don’t sweat high draw loads, but i’m finding that my Victron 702 is not an accurate indicator of charge. I think it calculates it based on amps out but doesn’t seem to jive with the readings I see on each of the batteries via their BMS panel. Some tweaking to do there. Agree that amps in and out will be the main indicator, but not sure yet how to accurately show that via the 702.

I would trust the Victron, which uses a precision shunt versus the on-board BMS, which *maybe* is using a hall effect sensor but more likely is guesstimating based on cell voltage.

I can't find anyone on youtube that cut one of these batteries open yet to take apart the BMS. All the recommended videos seem like commercials to me.

I just did a battery revamp and added 4 lithium batteries, stayed with 12v setup due to pre-existing 12v inverter charger. Very happy with it, They don’t sweat high draw loads, but i’m finding that my Victron 702 is not an accurate indicator of charge. I think it calculates it based on amps out but doesn’t seem to jive with the readings I see on each of the batteries via their BMS panel. Some tweaking to do there. Agree that amps in and out will be the main indicator, but not sure yet how to accurately show that via the 702.

Sounds like a great project!

GordonThree wrote:
Counting amps out vs amps in is even more important, IMHO.

I have a Victron BMV-702 for that. I think I'll also get the Victron Color Control system once we do this upgrade.

ependydad wrote:

GordonThree wrote:
48 volt. The higher the voltage the better. It will give the most margin between "full" and "empty".

With the lithium batteries, does that reasoning still stand? The drop-off for lithium is sharp with very little in the middle of charged vs. not.

Yes, applicable to any technology. On lithium you can't rely on voltage as an accurate state of charge indication, because of that flat discharge line. However having more margin is still a positive.

Counting amps out vs amps in is even more important, IMHO.

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Higher voltage also lends itself to more efficient conversion inside the inverter. Instead of having to amplify a 12v source with a gain of 10x to get 120v output, a 48v source only needs to be amplified 2.5x (this is over simplified but works as a demonstration). The amplification (boost) causes heat in the inverters's transformer and switches (transistors). The less work they have to do, the less heat they generate.

GordonThree wrote:
48 volt. The higher the voltage the better. It will give the most margin between "full" and "empty".

With the lithium batteries, does that reasoning still stand? The drop-off for lithium is sharp with very little in the middle of charged vs. not.