What gauge wire?

[pasusan]

I want to do it right and am not afraid to dig in (do the work and spend the money).

I've got a Progressive Dynamics PD 4645 converter (which I put in to replace a boiler type).

The length of cable from the battery to the converter is 12 feet. I am supposed to double that length to look at charts for the correct gauge, right?

The gauge of the wire in there now is 8 AWG. Some of the places I look say that's OK, some say 6 AWG, and some say 4 AWG.

What do you recommend, why, and what is your source?

Thanks very much.

[ktmrfs]

assuming the frame is a decent ground, equal to #0wire or so, which with a thick welded frame is highly likely, then with #8 wire at 40A you would see about a 0.45V drop in the wire. Going to #4 would drop that to 0.23V.

for comparison I have a 45A PD converter in the WFCO box with 30ft of #4 cable and chassis ground. voltage drop at 45A is about 0.3-0.4v about what I calculated. The PD has no problem going into bulk mode charging on startup with a pair of GC batteries even at 80%SOC. It will start and hold 45A quite a while.
your shorter run with #8 should yield similar results. going to #4 will hold 45A longer, but I think you'll find the difference in charge time from say 50% to 90% won't change by a huge amount.

Now if your frame is thin beams rather than std I beams and bolted rather than welded together, ground return resistance may be high enough to alter your results.

My frame is much better than #4/0 wire based on some measurements I did, roughly 1/3 the resistance of #4/0 wire.

[ktmrfs]

smkettner wrote:

pasusan wrote:
Using the wizard mode button I put it in boost mode which is supposed to be 14.4V. My remote display read 14.49 and my multimeter read 14.43 on the battery posts.

Repeat this test with battery starting below 12.2 volts.

using two different meters of unknown accuracy to try to measure voltage difference in the 10's of milivolts, is questionable. Try to use the meter at the battery posts AND converter output. you can then rely on getting a pretty accurate voltage drop measurement.

[tenbear]

Further to what SMK said, the thing that causes the voltage drop in the wire is high current. Just because you have the voltage at 14.4v doesn't mean the current will be high. You need a discharged battery so the battery will accept more current.

Ohm's law: voltage = current x resistance ( E=IR ).

[mena661]

X2 on testing with low battery SOC.

[time2roll]

pasusan wrote:
Using the wizard mode button I put it in boost mode which is supposed to be 14.4V. My remote display read 14.49 and my multimeter read 14.43 on the battery posts.

Repeat this test with battery starting below 12.2 volts.

[BFL13]

That test shows the converter does do its stages, but does not show what happens when you try to recharge low batteries using the 14.4v stage.

One test would be to start with low batteries (12.2v say) and not use the Wizard, but just see if the converter will go into the 14.4v stage by itself. If it won't, and you need to use the Wizard to make it do 14.4v, then you know you need fatter wire---if you want more amps at 14.4

So the next thing is to measure how many amps you are getting on low batteries with the existing wire after you force it into 14.4, and then decide if that is enough amps.

The big selling point of the PD IMO is that, unlike other some other converters, it does have the CW so you can force it to do 14.4 when it (and the some others) would not do so on its own. This can make up for having thin wires to some extent. Is that extent enough in your case for your needs?

If you don't have access to an ammeter that will measure 45 DC amps or so, then you would have to do some timing tests to replicate camping recharging but this can be a pain.

Another problem with backyard testing of converters is the 120v input you use. You can have lower voltage on an extension cord from the house than the higher voltage you get from your generator. Low 120v input voltage hurts the converter's DC output. You might need to run the gen for hours in the backyard to get the true picture.

[pasusan]

OP here.... I checked with my multimeter...

In Storage mode which is supposed to be 13.2V, the remote display read 13.35, and my multimeter read 13.28 on the battery posts.

Using the wizard mode button I put it in boost mode which is supposed to be 14.4V. My remote display read 14.49 and my multimeter read 14.43 on the battery posts.

At this point I'm not worried and maybe I won't need to change my wiring - but I will definitely be calling Randy at Best Converters next week and check with him.

[tenbear]

As I see it, #8 is safe. If you are happy with the charging time, leave the #8 wire as is. If you want faster charging, replace the #8 with a larger wire. If you are replacing the wire you might as well use #4. It doesn't cost much more than #6 and will reduce the charging time a little more. Basically what SMK said earlier. JMHO

[BFL13]

If your 45amper acts like a 35 amper on a 220AH bank if will take approx. 30 min longer to do a 50-90. (3 hrs vs 2.5 hrs)

If you upgrade the wire and get it to act like a 40amper (best you can hope for with w 45a PD--which are known not to do full amps at 14.4v anyway) you might save 15 min of that.

So it is all about that 15 minutes and how important that is for deciding what is "worth it."

Besides the "PD issue", to get full amps from any converter you have to mount them quite close to the battery with fat wire. Even then it is very sensitive what you get. On a 60 amper I got 59a with it close but when even closer (under two feet of #4) I got 63a.

If you mount the converter in with the power centre somewhere back in the rig, you are not going to get full amps even if you use a fat wire (where fat is as fat as is reasonable to work with.) You really need to do a deck mount within say two feet of the battery bank.

[RJsfishin]

I can only tell you that the PD 45 amp on 2 GP 27s @ 50% soc, is going to spent most of its time at 30-35 amps and less. The short time it will spend at 40-45 amps, is not worth haggling over when choosing wire size. Personally I think 4 ga is way overkill.
But then, I've read of 4 ga coming down off the roof for a few hi voltage solar panels, so there must be more to it than what I know.

[pasusan]

Bob Landry wrote:
Does anyone think that maybe the OP should go by the instructions in the installation manual?

The converter is a one to one swap - both 45 amp converters. The only thing about wire size my instruction manual says:

"Do NOT install a converter whose amperage rating is higher than the one originally installed in your application.
Doing so may cause wiring to overheat, resulting in damage to components and/or fire."

That being said the new converter has a boost mode which my old converter did not have. And I have read on here that without thicker wire the battery won't get the volts it needs for boost mode.

---The converter has been in operation for a few years now - I just want to make sure everything is working properly...



Thanks everyone for responding. Looks like folks are getting similar information that I got while looking at charts - different charts say different things.

That calculator that BFL13 linked to sure looks like I better go to 4 gauge. Thinking of measuring the volts at the battery while the converter is in different charging modes.

[DryCamper11]

MEXICOWANDERER wrote:
Anything larger than number six AMERICAN WIRE GAUGE would be a waste of good money.

I disagree. It depends on what he wants. If he just wants safety, #6 is fine for a PD providing a max of 45 amps. If he wants to be able to carry more current later, and do it safely, he might want to invest in #4. But, if he wants maximum speed of charging, as I do (to charge with shorter generator runtime), then the largest diameter wire he can fit and afford is desirable.

A PD converter does not have remote voltage sensing. That means it can't compensate for the voltage drop across the cables. My 460AH battery bank has a few milliohms of internal resistance. Unless you want to drop most of the voltage across the cables at the end of the charge cycle, you want cables with comparably low resistance.

My PD9280 will push 75+ amps into the battery even when there's only 0.1-0.2 voltage difference between the battery voltage and the charger output.

I moved my converter closer to the batteries and used 1/0 cables to minimize resistance. I would have used 4/0 if they would connect to the converter terminals. When I had smaller gauge charge cables and longer cables, the charge current dropped much faster/sooner because that entire 0.1-0.2 volt drop was across the cables - leaving nothing left to push current into the batteries. The converter responds by dropping current, which decreases the voltage drop across the cable, leaving voltage to push that reduced current into the batteries.

Personally, if I seldom camped in the boonies, I'd install #4, but if I wanted fast charging, I'd use 1/0 or better.

[ktmrfs]

Since you have #8 already there, unless it is easy to run new wire, I'd hook it up with #8 and give it a try. If your satisfied, your done, if not, then run a new wire, but then #6 or #4 welding cable is very readily available and easy to work with, pick one and go with it.

Whatever you do, go with high quality terminals properly installed.

More than likely, the hot run is your 12ft, but the ground is likely grounded to the trailer frame at the battery and at the converter. This is in the vast majority of cases, a much lower resistance path than a #6 or #8 wire. I did some measurements on my trailer frame ground and it is better than #4/0 AWG cable. Results will vary depending on frame construction and welding, but usually frame ground is better than a length of wire.

[Bob_Landry]

Does anyone think that maybe the OP should go by the instructions in the installation manual?