1 8D AGM, 900w solar

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1 8D AGM, 900w solar

January 16, 2014, 01:54:17 pm

Looking at boondock, will this set up work or do I really need another battery?

USES
Normal TV charge cell phones, no satellite or dvr, florescent and led in salon, gas:waterheater, refrig.

Re: 1 8D AGM, 900w solar

Reply #1 – January 16, 2014, 01:56:19 pm

You still need 12 volts for your fridge even though it uses gas to heat. I think one battery is way under what you need. You do not want to discharge it fully each time.

Re: 1 8D AGM, 900w solar

Reply #2 – January 16, 2014, 02:01:31 pm

Hmm..
thought it was a 100 ah battery. Will I use 40ah over night? Thought it was 20-30 without furnaces.

Im not smart enough to figure all the amp stuff out..

Re: 1 8D AGM, 900w solar

Reply #3 – January 16, 2014, 02:09:43 pm

I've got two 8D AGM's and 465 watts and we have no trouble with lights, TV, Microwave, coffee pot. 900 watts is plenty to fill the batteries up but then you have battery...I think I'd get another one.

Re: 1 8D AGM, 900w solar

Reply #4 – January 16, 2014, 02:25:41 pm

I have 3 8D agm and 750 solar. just remember the batteries are you storage bank. allways good to have lots available
John H

Re: 1 8D AGM, 900w solar

Reply #5 – January 16, 2014, 02:36:58 pm

John h,

Gotcha, just looking at the 40% use down and 60% charge up. Guess it would be better with 2. Can I use a wet cell and the AGM?

Re: 1 8D AGM, 900w solar

Reply #6 – January 16, 2014, 03:13:30 pm

I agree that the solar is fine but the battery us the weak link.

Re: 1 8D AGM, 900w solar

Reply #7 – January 16, 2014, 03:17:13 pm

Quote from: fouroureye – January 16, 2014, 02:36:58 pm

Gotcha, just looking at the 40% use down and 60% charge up. Guess it would be better with 2. Can I use a wet cell and the AGM?

If you only have one battery then a LOT of that charging power will not be used. On the plus side, you'll recharge that AGM pretty quickly every day. If you add another battery they'll stay in their comfort zone (as far as capacity) and see you through cloudy days better. Do you have an MPPT solar charge controller?

I don't think I would mix AGM and wet cell batteries. I have two wet cells for the house and one AGM for the starting battery. If you have a wet cell for the start battery you ccould pair that up with another wet cell for the house and move the AGM over to the start position. But you would be way better off with two AGMs together. I'm going to toss my two wet cell batteries when we get closer to snowbirding in 2016 and replace both of them with AGM.

Craig

Re: 1 8D AGM, 900w solar

Reply #8 – January 16, 2014, 04:19:32 pm

Adding like batteries will greatly extend their life. The less percentage you discharge each night, the longer they will last. A battery discharged to 10% DOD (depth of discharge) will last about 5X as long as a battery discharged to 50% DOD. A battery is considered dead at 10.1 volts.

A good read for anyone considering the purchase of batteries: Deep Cycle Battery FAQ

Pierce

Re: 1 8D AGM, 900w solar

Reply #9 – January 16, 2014, 04:26:33 pm

Pierce,

Good article. Looks like I need 2.
My old wet cells lasted 3-5 years at 1/3 of the cost of agm
What if I just sold the agm an went to wet?

Re: 1 8D AGM, 900w solar

Reply #10 – January 16, 2014, 06:31:34 pm

Quote from: fouroureye – January 16, 2014, 04:26:33 pm

Pierce,

Good article. Looks like I need 2.
My old wet cells lasted 3-5 years at 1/3 of the cost of agm
What if I just sold the agm an went to wet?

You could do that but won't two wet cells cost about the same as one AGM? Plus you'll have to monitor the water in the cells pretty carefully. At least I know that I have to. And the cells at the very back of the battery box seem to lose the most water, too. Of course, the hardest to get to.

Craig

Re: 1 8D AGM, 900w solar

Reply #11 – January 16, 2014, 06:53:14 pm

So I can mix batteries, just not recommended..

W ith a little maintenance, I will get a fancy pump, lol
180ah cost $186+ core, so 2 would be 372+ tax for 360ah, local
Use them for 4 years replace =744

Do the math on AGM (yes more ah, what 60?)

Guess this is a never ending question, considerations

The hd fork lift batteries are interesting, bet the cost is impressive.

Re: 1 8D AGM, 900w solar

Reply #12 – January 16, 2014, 09:05:04 pm

I was just in Autozone comparing battery prices and the 31 series are about the same price as the smaller batteries. Think they were $107. With a decent charger with temp sensor, they should not need that much attention. It's all I can do to carry one by the handles.

Watch Craigslist. I got my 6 batteries listing over $400 each for $35. They were 2 months old from a bankrupt company. The truck selling them had hundreds of them in the back. My neighbor put his on a shelf and when I got them for my car, they were still at 12.7V over a year later and had not been touched. CL was also where I found my PV panels.

For a DIYer, T-105s are what a lot of dry campers swear by. Have to modify the racks for them to fit. Wish I could remember where the well done blog went. I used 2 in my Buffalo bus with a Trace inverter while building a house. Fast idled the Detroit to charge them in the day. 300 amp brushless PTO alternator was stock.

Pierce

Re: 1 8D AGM, 900w solar

Reply #13 – January 16, 2014, 09:27:48 pm

Pierce,

Sound good, they are taller great deal you got.
CL hmmm will look. Ebay has 6 for 600 + core pick up in atl

Re: 1 8D AGM, 900w solar

Reply #14 – January 16, 2014, 11:01:45 pm

I use 4 T-145 6v batteries for the house.
They work fine and require little attention.
I paid about $100 each 4 years ago.

Re: 1 8D AGM, 900w solar

Reply #15 – January 17, 2014, 01:58:13 am

Solar at 900 watts will provide Max of 54amps, however, the realistic amps available will be about 30amps for 6 hours/day so 180 amphours/day.

For most days when boondocking, plan to recharge with half of the amphours available from your solar panels (90 amphours) and to cycle your batteries to 90% charged (see Pierce's explanation). Recharging a battery from 90% to 100% charged is only 60% efficient so you can use 50 amphours (60% of 90) and the battery capacity you need for 10% discharge is 500 amphours, which is two 8D batteries.

This will allow you to use 100 amphours some nights while discharging your two 8D batteries to 80% charged. Recharging batteries from 80% to 100% charged is about 70% efficient, so will require about 145 amphours which you have available.

You then have 35amphours available to run a ceiling fan during the day for ventilation.

If your 8D AGM battery is old, you could use it, however, you will discharging it to 80% most days and to 60% some days. This will work, but you will get about half as many cycles as with two 8D batteries.

To sum it up: For maximum battery life you need another 8D battery, however, your one 8D battery will work.

If you do not have an amphour meter, get one and learn how to use it.

Mixing a wet cell and an AGM in a coach battery bank will not work because the voltage required for absorption is different for the two batteries.

wa_desert_rat said:
"If you have a wet cell for the start battery you ccould pair that up with another wet cell for the house."

This sounds like pairing a start battery with a deep cycle for coach deep cycle service, which will not work well because the start battery will fail within a year.

You can use a "deep cycle" battery for starting, but you cannot use a start battery for "deep cycle".

My experience with using wet cell batteries for deep cycle was bad. I deep cycle my coach batteries more then 200 times per year. The wet cells out gasing caused rapid corrosion of the wires and battery posts - way too much work to keep clean.

If you will boondock only a few times a year - wet cells are fine for "deep cycle".

I am using two 8D AGM batteries and one 8D Gel for both coach and starting. The Gel provides half the amphours required and each AGM provides just a quarter of the amphours. The Gel battery is 12 years old while the AGM batteries are 3 years old.

Re: 1 8D AGM, 900w solar

Reply #16 – January 17, 2014, 07:26:58 am

John,
Here's some information on battery care that might interest

Deep Cycle Battery Maintenance

Re: 1 8D AGM, 900w solar

Reply #17 – January 17, 2014, 07:59:00 am

Wyatt,

Glad you looked and helped. I have read your boondock posts before. Curious you use the gell for both house and start?

Guess when agm goes bad, 4 years old. I will need to make som modifications and get at lease 1 additional battery. I have red tops for starting again 4 yrs old.
Thanks for all the advice!

Re: 1 8D AGM, 900w solar

Reply #18 – January 17, 2014, 11:07:43 am

Here is a photo of my battery installation. This was done without any welding and fairly easy. Sawzall, metal cutting band saw and drill are all that is needed. Six series 31 deep cycles could be installed instead of these without any further modifications and would be equivalent to three 8Ds. Not really any room for the same capacity if you used T-105 or T-145 6 volt batteries as they are too tall.

Pierce

Re: 1 8D AGM, 900w solar

Reply #19 – January 17, 2014, 11:18:23 am

Pierce,
U300 vs u280? In front of drivers rear wheel?
Great I have 2 racks there. The ATM takes up the top rack.

WoW 3.. that's what we need. When I'm ready will you help me understand the connections?

Re: 1 8D AGM, 900w solar

Reply #20 – January 17, 2014, 01:12:39 pm

John,

Yes, the same U280/U300. Glad to help with connections and send closeup photo. #1/2 aids are a Brother label machine and a digital camera. A must have when disconnecting the first time as these cables probably have the original codes faded out by now and many people put the wrong cables in the wrong places. My isolator and boost solenoid did not work when we got it because the wires were mixed up. Creates a lot of detective work, especially if you are on the road. Had me scratching my head for a while.

The other big help is blowing up the original electrical schematics at Kinko's. Super helpful in stressful situations with low light, bad glasses, etc. Bill Chaplin had made me a copy when they came to visit. They just roll up and go in a mailing tube. Still very appreciative! See you in a few, Bill.

Pierce

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