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Old 08-04-2019, 04:09 PM   #21
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Name: John
Trailer: Roamer 1
Smith Valley, Nevada
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Originally Posted by John in Santa Cruz View Post
for those who don't quite get what Raspy and I are saying.... pictures!

this way, each battery has the same amount of wiring in series with it. if both + and - were connected on the left, say, then the right battery would have additional resistance in the form of the bridging wires.
Yes. For charging and for loads.
I only exaggerate enough to compensate for being taken with a grain of salt.
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Old 08-04-2019, 08:04 PM   #22
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Name: Stu
Trailer: 2003 21RB Bigfoot
Coos Bay, Oregon
Posts: 115
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Originally Posted by John in Santa Cruz View Post
you also should have the loads connected that way.
Good point. I didn't have the batteries in the truck bed connected that way but get why that is much better. Will be sure to wire them that way.

All of the above must be to put off having to say that parallel 12 volt batteries are not optimum as they will not take charge evenly depending on their internal resistance.
The lower impedance battery will take more of the current and the higher less.
This means that the weaker battery will get the lower charge rate. If they are connected and on a charger that is three or so stages they will get charges as the charger changes the float and bulk charge voltages and currents and occasionally goes higher to "Churn" and desulphate the batteries.
All of that said the voltage on the batteries will be the same, but the current to each will be different. You could easily have all of the current going to one battery and none to the other.
This is what I've been considering. NOCO recommends charging the batteries individually (see link I posted earlier) with a few exceptions (it appears charging two 6V in series with a 12V smart charger is OK). I think a lot of the benefit of a smart charger would be negated if you connected it to the first "+" and the last "-" in the parallel chain. No two batteries are ever going to be exactly the same except the day they leave the factory (maybe?). The smart charger uses an 8 step process (analyze, diagnose, recovery/desulfation (if needed), initialize, bulk, absorption, optimization and maintenance). For example, I don't think the smart charger could pick out the one battery in the chain that needed desulfation.

After researching and thinking about it here is my plan (for the minute ):
1.) Move 3 of the 4 12V group 24's into the trailer. When one goes out replace with a group 27. They will barely fit in the storage under the bench in front of the load center/converter. I will install a 3 1/2" 12V fan with switch. I'll keep the extra group 24 and swap it in/out as I use it for the electric motor for my boat.
2.) Install a NOCO Gen4 ($300 ) 4 bank charger. Hook it up to each battery individually. Leave the 3-prong to plug into either shore power or the generator. The Gen4 provides 10 amps per bank and should fully charge all 4 batteries in 5-ish hours (if 50% discharged). I considered the Genius G4Mini ($180) but it's only 1.1 amp/bank - it would take forever to charge. Also, a large single bank charger like the Genius G26000 ($200) is still only 26 amps. Not sure it would even work very well (as discussed before) and it would still take a lot longer.

Switching to charging mode from boon-docking would consist of:
1.) Turn Perko switch to "off" to isolate the batteries from the MagnaTec charger/converter (which BTW I think is working somewhat).
2.) Plug trailer into generator or shore power.
3.) Plug NOCO Gen4 into generator or shore power.
4.) Turn converter on to supply trailer 12V loads while charging.

Planning on retiring in 23 months and if not completely full-timing taking some very long duration trips I got the trailer a few years ago and I am still figuring out exactly how we will use it. I see us rarely being plugged into shore power, probably average less than 1 night a week. On our trip to Alaska last year we were plugged in a total of 2 nights for 60+ days

PS: I do plan to get a 100W deployable solar panel before going full-time. Should keep things topped off if we are at lower latitudes.

Thanks for the discussion
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Old 08-30-2019, 07:34 PM   #23
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Name: Stu
Trailer: 2003 21RB Bigfoot
Coos Bay, Oregon
Posts: 115
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Here's a pic of the upgrade:

I found a NWOB NOCO Genius G4 on eBay for $220 shipped I already had the 300W Go Power Inverter.
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