Community Forums

bobmoore1954 · 07-20-2018, 03:07 PM

I have a Newmar Ventana with (6) Interstate GC2-ECL-UT batteries. They're rated at 225 amp-hrs @ 20 hrs.

My question is what I can set the Magnum Inverter/Charger to when I'm dry camping. I'd like to recharge the batteries as quickly as I can.

Am I safe increasing the max charge rate to 100%? It's currently set at 80%.

The Magnum charger has an output of 100 ADC, so a 100% setting would limit the battery charging rate to 100 amps.

twinboat · 07-20-2018, 03:28 PM

With 675 AH of capacity and the typical flooded battery, max charge rate of 15%, you can set your charging rate to 100 amps.

I'm not sure if it will make that much difference, unless you are drawing your batteries down below 50% state of charge.

Do you hit the 80 amp threshold now, while charging ?
How long before the amps start tapering off due to internal resistance ?

bobmoore1954 · 07-20-2018, 04:19 PM

My batteries were overly discharged, to around 11.4v. So they charged for 4.5 hours at 85 amps before batteries got to 14.4 volts and the amps started to drop.

We're in Alaska dry camping, it has been 4 days since we've had shore power. And we haven't driven much.

Wonder how many hours of driving is necessary to fully charge the house batteries?

Soppy · 07-20-2018, 06:32 PM

Since you have 3 sets of batteries in parallel , at 100 amps charging from your inverter , each battery will be charged at about 33 amps. Should be no problem.

The number of hours driving to fully charge the battery bank can be hard to compute. There are quite a few variables that come into play . The alternator size , distance from the alternator to the battery bank (for voltage drop) and the operating voltage of the alternator. Just as a guess , if your bank has been discharged to 50% , it could take in excess of 6 hours driving to charge the bank assuming your alternator will be charging the batteries at 50 amps.

NealC · 07-21-2018, 02:26 AM

C/10 is the recommended rate so 70 AMPS is what you should set. (68 to be precise)

bobmoore1954 · 07-21-2018, 09:21 AM

What is 'C'?

NealC · 07-21-2018, 09:23 AM

Here is a link to assist: INTERSTATE DEEP CYCLE BATTERIES CHARGING RECOMMENDATION

twinboat · 07-21-2018, 09:47 AM

C is capacity ÷ % of its capacity.

A 200 AH battery will have a 20 amp charge rate at C/10.

Flooded batteries charging rate varries between 13% and 15%. Not sure where the 10% came from.

Winemaker2 · 07-23-2018, 05:04 AM

Here is a good article on battery charging times. It deals w AGMs but I believe the principles are correct for FLAs just need to apply the correct rates.
The message is that for complete charging times are much longer than the simple math would lead one to believe.

bobmoore1954 · 07-25-2018, 01:28 PM

Looks like there are several views on this.

I just found an 'Interstate' brochure which says the following:

'Watch the Amps. A charger should provide a maximum of 20 Amps for each 100 Ah of the battery'.

So in my case, that'd be (675 Ah / 100 Ah) * 20 Amps = 135 Amps. My charger will only deliver about 115 amps.

Finance · 07-26-2018, 01:53 PM

Generators and fuel cost more than batteries. Charge at max when off grid. Any trade off in diminished battery life is less costly than more runtime on the gen.

You'll never get full charge off a gen in most cases anyway. Need a healthy solar system for that. The final ten percent of charge takes hours, it's a total waste to run a generator for that. Aim for a cycle between 70-90 percent and your batteries will thank you. Top charge and equalize them periodically on shore power.

bobmoore1954 · 07-26-2018, 08:31 PM

Thanks, that’s kind of what I’ve concluded. In the L48, we have shore power most of the time. But now, we’re in Alaska and have lived off of the generator for over a week. I charge until the controller says I’m in ‘absorb charge’ and I see the amps drop. I have it set to automatically start the generator when the batteries get to 12.2 volts. So far, so good.