Battery Cable Sizing - PD9260

Instead of thinking the converter pushes think of the battery as pulling. The battery will "accept" a certain number of amps, where at any SOC, it will accept more amps if you raise the voltage. (That is why they use 14.4 instead of 13.6 so it will accept more amps)

At any chosen voltage, the battery will stop accepting that many amps when it gets to a certain SOC, so after that if voltage is held the same, amps must taper as "acceptance rate" declines as SOC continues to rise.

You can see it all here in my famous fantastic ugly graph, which I built after reading up on this stuff in Barre's book:

http://www.bestconverter.com/Books_c_67.html

I am about 25' from the converter to the batteries, the factory had installed a #6 postitive wire and using the frame as the ground path. I added a #4 in parallel to the #6 giving me an effective #2, and also replaced the pigtails to the frame on either end with #2.

BFL

As I understand your last post, if you have a BIG BATTERY, heavily discharged, that is when the converter will push the highest amps to the battery if the wiring supports that much amperage. If you have a small battery, lightly discharged, small wiring, that will produce a less than max amp push to the battery.

Is this correct?

doughere wrote:
When I installed a PD9260 I installed it in the compartment next to the battery; a pair of GC. I used battery cables from the local auto parts store, 3 feet each.

My intent was to get as much into the battery as possible when on gen.

I seldom see anywhere near 60A; usually not much over 40A and that only for a short time.

I'd think of upgrading the cable if the intent is to charge as rapidly as possible. For general use the existing is fine.

If the intent is to run an inverter somewhere then you need to rethink everything.

Regards,
Doug

To understand this we need the battery bank's true capacity and SOC at the beginning of the recharge.

Let's say the PD 60amper will do 55 amps when wired so it can. On two batts at 220AH you have to be under 72% SOC to get any bulk stage, after that it is all tapering amps in Absorption (due to the battery's "natural acceptance rate" )

If it kicks off at 40amps and tapers that should mean you are starting at approx. 77% SOC.

However if it is not wired so it can do 55a then it acts like it is on a smaller battery bank than that 220AH example (higher wire R looks like a smaller battery to the converter)

On a smaller battery that means your 40a is like having a higher charging rate (amps/capacity) so your taper starts at a lower SOC so now you have to be even lower than that in SOC to get any bulk stage.

Same thing if batts are sulfated to have less capacity than thought. Smaller capacity means higher charging rate, earlier tapering. (lower acceptance rate)

So you can have any, some, or all of these to explain the 40a:
-wiring too long/thin
-connections
-batteries sulfated
-starting at high SOC

(I left out any 120v input issues)

WOW, current carrying capacity of 4GA wire (Continous duty): 59.626

Which is close enough to 60 so as to say Good enough

My recommendation, would be 2GA so as to reduce voltage drop.

If you want to compute the voltage drop. E=IR and R=0.2485 ohms per thousand feet or .0002485 ohms per foot.

So a 10 foot run would be 60*.0002485*10 or 0.1491 volts. if I did not drop a decmil anywhere.

The PD has a design flaw. They won't output 60A. If you want to get anywhere near 60A you need heavy cables (2 awg or better).

Sal

doughere wrote:

I seldom see anywhere near 60A; usually not much over 40A and that only for a short time.

I'd think of upgrading the cable if the intent is to charge as rapidly as possible. For general use the existing is fine.

When I installed a PD9260 I installed it in the compartment next to the battery; a pair of GC. I used battery cables from the local auto parts store, 3 feet each.

My intent was to get as much into the battery as possible when on gen.

I seldom see anywhere near 60A; usually not much over 40A and that only for a short time.

I'd think of upgrading the cable if the intent is to charge as rapidly as possible. For general use the existing is fine.

If the intent is to run an inverter somewhere then you need to rethink everything.

Regards,
Doug

To evaluate the wiring upgrade option, he must decide if the generator time saved is worth the trouble of doing the wiring change.

Let's say he gets 35 amps at 14.4 now, and that with a wiring upgrade he will get 55 amps at 14.4. Time to do a 50-90 on two batts (220AH bank) goes from 3 hrs now to 2.5 hrs.

How many 50-90s does he do a week for how many weeks? How is the solar doing?

If he takes advantage of the generator running to also do some other chores that need 120v, then he might not get any benefit from an upgrade in the wiring. We don't know his camping routines.

With the converter running at full amps at first, he would have to wait until amps taper somewhat to get enough "room" to run his other things. If those other things take an hour and he can't start until hour 2, then the gen time will be three hours anyway.

Whatever, he is the only one who can say what would be worth it to him.

When I installed my PD9260 I replaced the #8 wire with #4. I wasn't worried about the current capacity of the #8 wire but the resistance. The wire was about 17' and I wanted most of the 14.4v to get to the battery.

Ron, if you use the frame for ground connection part of the wire run, you can lower the total feet in the equation for calculating wire size. The frame will have very low resistance.

If you have a fifteen ft. run, 60 amps at 14.5v w 4 awg voltage drop is 3% or .45V, with 20 amps at 14.5v using 4awg drop is 1% or .15v.
The 2awg double run is: at 60 amps, 14.5v- 1% .14v, 20 amps at 14.5 .32% .047v drop.

Here is the calculator if you want to play around with different conductor sizes.