Jumper for Batterys in Series

Ideally yes. they should be, same size or larger.

But for that short a run it is not as important as it is for longer runs. Size is determined by several things

the length of the run, the current draw, the type of wire.

theoldwizard1 wrote:
I would also get rid of the wing nuts and use stainless lock washer and nuts.

I use stainless wing nuts, no washer.

Last weekend I pulled off one jumper to clean some corrosion. The actual connection surface was perfectly clean. I like the wingnuts to remind me or anyone else to not over tighten the terminals.

bpounds wrote:
Instead of comparing the series jumper size to the primary cables size, consider the cable size needed to handle the maximum current draw. The primary cables in the OP's pic are oversized for some reason. Not sure why, but there is no reason why the jumper has to match those.

The reason for oversize wire is to reduce the voltage drop, thus getting more of the voltage the converter produces in bulk mode to the battery.

#6 wire would handle the current but would have a large voltage drop at 60A. With 20' of wire, ground and positive, and a bulk voltage of 14.4v the voltage at the end would be 13.93v, not counting losses due to connectors, fuses, etc. With #2 wire the voltage would be 14.21v. Not a huge difference but enough to slow the charging time considerably.

westend wrote:

bpounds wrote:

westend wrote:
bpounds, how much voltage drop exists between your converter and the batteries?

Never checked it.

I do have a voltmeter permanently wired into the chassis harness. Based on that I see the voltages that are appropriate for the converter modes. If there is a drop, it can't be more than a few hundredths of a volt. I see 13.6x volts in boost, and 13.2x in float, which is right on the rating.

On the other hand, my crappy WFCO converter has never gone into bulk mode. But that is a common complaint with those converters, and I don't believe it is due to cable size or distance. I've been planning to upgrade to a PD4600 for the entire 6 years that I've owned the trailer, but it just keeps on performing for us, and I just keep procrastinating on the purchase. The batteries are about 7-8yrs old, and I moved them over from our last trailer. So I can't complain about that either.

Thank you. I guess we could say that the existing wire size in your trailer is working to your satisfaction.

:R

time2roll wrote:
Depends on the load but in best practice yes the jumper should have the ampacity of the largest circuit as a minimum.

CORRECT !

Without more data, it is hard to say for certain if the gauge is "adequate", but it is very short.

I would also get rid of the wing nuts and use stainless lock wasker and nuts.

Absurdity got carried to a superlative when I repaired major wiring screwups on a 55' Passport sloop. A revamped Delco 10DN alternator (Balmar 130-amp rating). Would you believe 2/0 marine cable crunched to a lug with a 5/16" hole?

While even 10 gauge AWG wire can easily support 80 amperes in a 16" run, the terminals present the biggest limitation. 6 AWG would pass 140 amperes at a voltage drop too insignificant to mention. I went through a runaround at an Auto Parts store last year in San Diego. Needed 6 gauge wire. Not AWG, SAE would have done fine. They produced straight strand cable with fat insulation with a conductor closer to 7 gauge than 6. Off shore supply? I do not know. Unless a 2000+ watt inverter is needed 6 AWG cable like what genuinedealz offers would be more than enough to series bridge.

My 2-volt cell bank is series connected with 1/0 AWG. The main cables are 350 MCM which id 40% larger than AWG 4/0 cable. The 350 MCM feeds a 500+ ampere battery charging potential.

Fighting a nest of ------off anacondas to access fill caps is not good planning. I have encountered too many snapped GC220 terminal posts to suit me. And a surprising number of folks dwell on series cable overkill and ignore the chassis to house interconnect.

The next time your motorhome house batteries get discharged check the voltage drop between the alternator's battery output stud and the house battery positive post. You will be dismayed.

bpounds wrote:

westend wrote:
bpounds, how much voltage drop exists between your converter and the batteries?

Never checked it.

I do have a voltmeter permanently wired into the chassis harness. Based on that I see the voltages that are appropriate for the converter modes. If there is a drop, it can't be more than a few hundredths of a volt. I see 13.6x volts in boost, and 13.2x in float, which is right on the rating.

On the other hand, my crappy WFCO converter has never gone into bulk mode. But that is a common complaint with those converters, and I don't believe it is due to cable size or distance. I've been planning to upgrade to a PD4600 for the entire 6 years that I've owned the trailer, but it just keeps on performing for us, and I just keep procrastinating on the purchase. The batteries are about 7-8yrs old, and I moved them over from our last trailer. So I can't complain about that either.

Thank you. I guess we could say that the existing wire size in your trailer is working to your satisfaction.

westend wrote:
bpounds, how much voltage drop exists between your converter and the batteries?

Never checked it.

I do have a voltmeter permanently wired into the chassis harness. Based on that I see the voltages that are appropriate for the converter modes. If there is a drop, it can't be more than a few hundredths of a volt. I see 13.6x volts in boost, and 13.2x in float, which is right on the rating.

On the other hand, my crappy WFCO converter has never gone into bulk mode. But that is a common complaint with those converters, and I don't believe it is due to cable size or distance. I've been planning to upgrade to a PD4600 for the entire 6 years that I've owned the trailer, but it just keeps on performing for us, and I just keep procrastinating on the purchase. The batteries are about 7-8yrs old, and I moved them over from our last trailer. So I can't complain about that either.

bpounds, how much voltage drop exists between your converter and the batteries?

If you looked at the image of that battery pair carefully, the jumper wire would stand out as being wrong in a number of ways:
1) It is too long for the application and the length interferes with the cap on one of the battery cells.
2)The jumper is badly corroded at one end.
3)Both cable end terminations are poor with exposed wire between the lug and cable insulation.
4)One cable end is taped with common electrical tape.
5) Both cable lugs appear to be very flimsy and are probably corroded to less than 50% of their original size.

I'm only digging in on this so others that aren't as experienced don't assume that the jumper cable is "OK" and replacing it isn't a "waste of money". It is one of the poorer cable installations I've seen in real life or on this Forum. I'd bet that the owner of those batteries visited an auto parts store and bought what was available on the shelf.