I Think I Just Bought Way Too Much Battery

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.

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

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?

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.

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

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.

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.

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

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.