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04-21-2022, 12:02 PM
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#21
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Member
Join Date: Jul 2021
Location: Hampton, Virginia
Trailer: 22' 17B
Posts: 69
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Quote:
Originally Posted by ridinbarney
Other than positive to positive, does it matter which positive/negative battery post I connect my solar leads to on my 2 12v batteries in a parallel configuration? Thanks
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I'm reasonably certain if in parallel you'd have to connect wholly to each battery at a time. Of course it's not ideal to have different charge levels on your batteries. Probably a better way to do that setup
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04-21-2022, 12:09 PM
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#22
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Site Team
Join Date: Dec 2017
Location: Mid Left Coast, California
Trailer: 2014 Escape 21
Posts: 5,122
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Quote:
Originally Posted by ridinbarney
Other than positive to positive, does it matter which positive/negative battery post I connect my solar leads to on my 2 12v batteries in a parallel configuration? Thanks
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ideally, you connect positive to one battery and negative to the other, this is true for both loads and chargers. this way the voltage drop in the bridging wires is 'balanced', both batts will have the same series resistance, assuming the + and - paralleling/bridging wires are the same gauge and length.
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04-21-2022, 02:20 PM
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#23
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Senior Member
Join Date: Apr 2014
Location: Arvada, Colorado
Trailer: 2015 E'21 - 'Velocity'. Tow: Toyota Tacoma V6, 4X4, manual.
Posts: 1,684
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Quote:
Originally Posted by John in Santa Cruz
ideally, you connect positive to one battery and negative to the other, this is true for both loads and chargers. this way the voltage drop in the bridging wires is 'balanced', both batts will have the same series resistance, assuming the + and - paralleling/bridging wires are the same gauge and length.
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This illustrates John's suggested wiring for parallel batteries. Note that "load" is both power out and power in (solar, charger, etc.).
In my case, I attached everything to one battery and after 7 years never noticed a problem. Using a heavy gauge wire to connect the two batteries will minimize any imbalance.
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04-21-2022, 04:17 PM
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#24
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Site Team
Join Date: Dec 2017
Location: Mid Left Coast, California
Trailer: 2014 Escape 21
Posts: 5,122
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the imbalance of paralleled batteries is more significant under heavy current loads where the resistance of even a foot of awg4 or whatever will start to count. since one battery is 'behind' an extra foot of + *and* an extra foot of -, it counts as 2 feet. AWG4 wire is about 1/4 ohm per 1000 feet, so thats .0005 ohms for 2 feet... at 100 amps (maybe running a big inverter), there will be a 0.05 volt drop (1/20th of a volt), thats about 5 watts lost in the wiring, too.
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04-21-2022, 06:44 PM
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#25
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Senior Member
Join Date: Apr 2014
Location: Arvada, Colorado
Trailer: 2015 E'21 - 'Velocity'. Tow: Toyota Tacoma V6, 4X4, manual.
Posts: 1,684
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Quote:
Originally Posted by John in Santa Cruz
the imbalance of paralleled batteries is more significant under heavy current loads where the resistance of even a foot of awg4 or whatever will start to count. since one battery is 'behind' an extra foot of + *and* an extra foot of -, it counts as 2 feet. AWG4 wire is about 1/4 ohm per 1000 feet, so thats .0005 ohms for 2 feet... at 100 amps (maybe running a big inverter), there will be a 0.05 volt drop (1/20th of a volt), thats about 5 watts lost in the wiring, too.
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Thanks for doing the math. On a bad day we might have pulled 20 amps for a few moments. That would be about 1 watt lost. But watts a watt between friends?
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04-22-2022, 10:17 AM
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#26
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Member
Join Date: Nov 2018
Location: Arcata, California
Trailer: 2019 Escape 17B
Posts: 31
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Quote:
Originally Posted by nomade do vento
I am looking at this same suitcase. However I am leaning towards the solar being hooked up and into the 7 pin. This places the solar at the front of the trailer which receives the most sun. Has anyone done this?
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my husband connected ours to the 7-pin connector and it seems to work fine so far.
__________________
Omi
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04-22-2022, 08:17 PM
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#27
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Site Team
Join Date: Dec 2017
Location: Mid Left Coast, California
Trailer: 2014 Escape 21
Posts: 5,122
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if you have a rear battery, like the 21C, the 7 blade is like 25 feet of wiring away from the battery, this will cause some voltage drop which for lead acid charging is fairly significant. a 100W solar panel is good for 6-8 amps, 25 feet or so of AWG 8 wire from the hitch to the battery is 0.175 ohms, thats around a 1.4 volt drop at 8 amps or ` volt drop at 6 amps, so if the solar panel is outputting 13.8V for the bulk charge phase, the battery would only be seeing 12.4V, which is too low to charge it. so what happens is, the current drops way down, the voltage loss goes down too, and the battery charges, just much slower than it otherwise should.
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