I Think I Just Bought Way Too Much Battery

[4gnomad]

Hi guys, I'm hoping I'm wrong and someone will point something out to me that I haven't considered. I just purchased 2 L-16 batteries from some off-brand (that is supposedly US Battery underneath it all) that cost me $810. They're 6V, 400AH, which, I thought, was going to be awesome for boondocking. I bought them, the seller ordered them and delivered them, and in the meantime I looked up the 'right' way to charge the bank.

From what I can tell from the spec sheet the "charge characteristic curve" (which is here: http://www.vision-batt.com/site/product_files/EVL16-400A-AM.pdf) has the charging current at .25CA. I think that means that these 400AH batteries want to be charged at 100A, which is a TON of amps to be pushing for my little class B RoadTrek (in fact, I think it's a 30A electrical system so I can't). The most I can reasonably expect to push is 33A, and that's with an install of 4 100W 12V solar panels on the roof.

So my question is, if this pair wants 100A and I'm only able to push 33A (max, not including management/wiring losses), and I going to sulfate these things like crazy really quickly? FWIW they're AGM, which I think tolerate lower charging currents a bit better, but I think it's still not a great situation.

Any thoughts or clarifications on what I'm getting wrong here are really appreciated. Or, if I'm understanding the situation correctly, confirmation of that. I'm thinking I need to off-load these brand new L16s and get a more modest 12V bank right now.

[JamesJudasPries]

4gnomad wrote:
Just to follow up on this:

1. Yep, I've got the current L16s in a closet in the front behind the driver's seat.

2. This is a 1994 RoadTrek Versatile with the stock MagnaTek converter/charger. The converter is 32A, but the charger circuit is labeled 15A. I'll have to upgrade to probably a Progressive Dynamics 80A converter/charger. I'll also have to upgrade the wiring on the current 15A circuit to carry that current (this is the part I'm not looking forward to).

3. As someone mentioned (thank you!) apparently I can't just drop in these new batteries as a replacement for the existing marine. Specifically some basic wiring sheets I looked at seem to indicate that there isn't any additional voltage regulation between the alternator and the coach battery so I guess I'll need to add that to ensure my new AGMs don't get overcharged while driving.

You can be assured that you will never overcharge a 400 amp hour battery bank from your alternator charging circuit. If this charge path is not upgraded there's a chance it will blow the fuse or reset-able breaker if the batteries are low and you start driving. Then again maybe not if the wire is too thin, as much factory wiring is especially of that year of conversion.

So you may want to upgrade the wiring to say 2 gauge or larger and fuse it at 100 amps. This wire should go directly to the alternator positive post and then a very short distance later a fuse, because connecting it to the starting battery would have you limited to the fairly small charge wire from the factory charging circuit.

Now, some may argue that this may strain the alternator, and this may be true with your 400 amp battery bank. However, chances are the alternator will only put out 13.6 volts when warm, effectively slowing the charging current. A lot of vehicles have temperature controlled regulation factored into the alternator output as well.

Don't be surprised measuring around 100 amps being output if the van engine is cold and the batteries are low, especially since they are AGM. This could all depend on the power of the alternator as well, could be 75 to 120 amp on a dodge chassis.

So in a nutshell, if you leave the vehicle wiring path alone, chances are it will be inadequate and always undercharge your batteries. Possibly tripping the circuit protection as well if all your connections are good quality and the factory wire isn't micro sized.

If you upgrade your path, fuse at both ends, buy a new solenoid or non diode based isolator, and your alternator may get a workout but your batteries will actually charge.

[4gnomad]

They're actually "Vision" and appear to be Chinese, but when I talked to the guy who delivered them and works with these systems all the time he told me they were really rebranded US Battery underneath it all. I'm not entirely sure what to make of the conflicting information but he seemed like a trustworthy guy. The data sheet is here and definitely seems to imply .25CA. On a pair of these in series for 12V I think that's 100A @ 12V. Am I misunderstanding something? http://www.vision-batt.com/site/product_files/EVL16-400A-AM.pdf

[time2roll]

If they are US Battery it looks like they are limited to 65 amps so a 55 to 60 amp converter might be better.

Float would be 13.6 max so maybe a cut off switch when headed out with a tip top fully charged battery.

http://usbattery.com/wp-content/uploads/2016/05/usb_agm_L16_DATA_2016.pdf

What brand are they exactly?

[4gnomad]

Just to follow up on this:

1. Yep, I've got the current L16s in a closet in the front behind the driver's seat.

2. This is a 1994 RoadTrek Versatile with the stock MagnaTek converter/charger. The converter is 32A, but the charger circuit is labeled 15A. I'll have to upgrade to probably a Progressive Dynamics 80A converter/charger. I'll also have to upgrade the wiring on the current 15A circuit to carry that current (this is the part I'm not looking forward to).

3. As someone mentioned (thank you!) apparently I can't just drop in these new batteries as a replacement for the existing marine. Specifically some basic wiring sheets I looked at seem to indicate that there isn't any additional voltage regulation between the alternator and the coach battery so I guess I'll need to add that to ensure my new AGMs don't get overcharged while driving.

[tplife]

AGM batteries can be mounted under the dinette, upside down, with no venting required.

[noteven]

Best Converter

[4gnomad]

Thanks for your help everyone, I'm going to add a better converter to handle the requisite amperage and then recharge overnight from shore power regularly.

[booster]

Charge voltage is important to keep batteries healthy, as they need to be brought to what the manufacturer says is the best voltage to dissolve sulfate and get to a full charge. But--voltage will not tell you if the battery is full, and neither will time or most of the algorithms. The only way to reliably tell if you are completely full is to look at the amps going to the battery (not out of the charger). Second best would be to look at amp hours returned compared to used and adjust with charge efficiency.

Most chargers will chronically undercharge a very big battery bank, as the absorption timers are set to be safe for smaller banks. Even the ones that claim to indirectly measure the state of charge, bank size, etc and adjust the timers usually will be on the undercharge side to be safer. The figure slower death by undercharging is better than quicker death by overcharging. If you know the amps the battery is receiving, you know if you are charged, or not.

[time2roll]

Charging voltage is more important than amps. Get Progressive Dynamics or IOTA converter for best results. Your 120 vac 30 amp supply can drive the largest of each at 12vdc 80 or 90 amps. 55 or 60 amp versions are fine also. Just takes longer.

Yea L-16 in a B is a bit crazy... in a good way :B

[2oldman]

4gnomad wrote:
I'm just wondering how bad it will be if I'm only charging them at .0825CA instead of the .25CA that the PDF indicates as a "standard" charge. I don't know how to assess the consequences of that, or whether it's enough to prevent sulfation..

Good question.

I'm not in possession of that kind of knowledge, perhaps google or someone here is. It's my contention that keeping them as charged as possible without letting them sit, at say, 50% for too long is fine.

I think the problem you will have (depending on usage) is that a 99% charge is going to take a long time at .08.

[4gnomad]

They don't fit in the existing compartment. They're housed in a closet space that is right next to the existing compartment. My understanding is that the charge current varies by manufacturer, and I'm just wondering how bad it will be if I'm only charging them at .0825CA instead of the .25CA that the PDF indicates as a "standard" charge. I don't know how to assess the consequences of that, or whether it's enough to prevent sulfation..

[pianotuna]

Hi 4g,

Physical space requirements will almost certainly be different than for the marine battery.

My 139.2 amp-hour AGM's are limited to 27 amps @ (nominal) 12 volts for recharging.

[4gnomad]

Uh oh, now I'm a little confused. I did think that dropping in these two L16s would be a drop-in replacement for my much smaller current marine battery. Aren't the components that require upgrade limited to the charge converter + wiring to the terminals (+ the equivalents in solar when I install it)? The loads in the rig won't change substantially.

[4gnomad]

Wow, that was quick. I'm not sure of the converter yet, but I'm willing to replace it. In terms of the 33A that I can produce on my own (solar) that's 4 100W panels on the roof + a (theoretical as I haven't installed solar yet) MPPT controller.

Each battery is 100lb - actually more manageable than I expected. We'll see how they perform.

So it sounds like if I connect to 30A 120V shore power for a full day for a recharge (with a sufficient converter) I'll be fine in terms of preventing sulfation, but if I'm just recharging from solar at 33A, 12V I'll just be at .0825CA which will generally be undercharging the pair, right? That's my main concern, I was planning to go to 25% DOD on these so they would last forever, but if I'm killing them by only charging at .0825CA anyway I might as well not install solar and just rely on hooking up to shore power at a park. Is there some rule of thumb that describes how frequently you need a faster charge to keep things mixed up? Every time, every 5 cycles, every 10? I guess given that there are enough amps coming in with shore power it's the frequency of desulfation I need to figure out. I'll see if that's a phrase Google knows. 🙂