Cable Requirements for PD4655 Converter

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otrfun wrote:
Wow, as always, thanks to everybody for all this helpful info! Most of this stuff is a bit too technical for me, but I'm learning little by little.

To answer smkettner's question, if I were to purchase the PD4655 I would be adding a 2nd 24 series battery. About a week ago I tried a few days of dry camping and noticed I barely could make it through the day without draining my single 24 below 20%.

The 8-10 ft. run of 6 gauge cable is a one-way, positive-side, measurement only (from the battery to the converter). I kinda get the overall impression this setup will limit my maximum charge current (in 14.4 volt bulk mode) about 10-20% with this size/length of cable. Is this a reasonable assumption? Assuming it is, it doesn't seem like it's worth my time and effort to swap out this 8-10 ft. of 6 gauge cable (for a larger gauge) to save 30-45 minutes of charge time right now. If I get more serious about dry camping it may be something I may consider doing at a later time.

Right now, I believe my WFCO 8655 is giving me a 50% (12.2 volt) to 80-85% (12.6 volt) charge in approx. 4-5 hours. If I used my existing 8-10 ft. of 6 gauge cable with a PD 4655 would it be reasonable to expect this 50% to 80-85% charge time to be cut in half, to 2-3 hours?

Thanks!

If it takes 4-5 hours to get single 12V charged I highly suspect that the WFCO has the "classic" not going into boost mode and sticking at 13.6v.

With the #6 wire and the PD you should be able to get from 50% to 80-85% in 2 hours or less with a single 12V. Even with a pair of 12V you should be able to get to 85% S0C in 4 hours or less.

As a point of comparison. I have 4 T-125 GC batteries and a PD65A converter. In 4-5 hours I can get the batteries from 50% to 85% or so consistently. Thats a 500AH battery bank, not a single 85-100AH Battery.

Now getting from 85-90% all the way to 100%, another story. At that point your down in acceptance current such that it takes almost as long to go from 90%-100% as from 50% to 90%.

The OP seems to be charging at 13.6v now but with the PD and CW would be charging at 14.4. Going to 14.4 would increase battery acceptance rate by about 1/2 in amps.

Say charging went from 40 to 60 amps by doing that. 50-80 on 160AH is 60AH 1.5 hours at 40 vs 1 hour at 60 doesn't work quite like that, but think of saving half an hour gen time on a 50-80 with two 24s by using 14.4 vs 13.6. That's with the same #6 wiring

If you could get the WFCO to do its 14.4 then no reason to get the PD. However many people report no luck with trying that, while others have no problems getting the 14.4.

My experience with PD 45amp charger with two type 24 batteries has been that amps taper off very quickly and I doubt 55amp is going to give you dramatically better charging time whether you use 6 or 4 wire - just my 02.

The #6 is fine with a pair of 24s. I don't think you will see more than a slight improvement going to larger wire. Of course if you have some #4/#2 lying around and the pull is easy then go for it.

The answer to your last question is you are not going to cut your charging time in half.

In your particular case, adding a second group 24 battery will double your usage time for both batteries to 20%. Better yet, the current usage time would drag the pair to 40%soc. Much better for battery life. Your current one is headed to an early demise.

Checking out how well a second battery will work is simple. Just put it on the ground near the first battery and connect them in parallel with a set of jumper-cables. Only need to connect for usage, or charging.

You will most likely find that your current charger can charge both batteries in only about 25% more time than spent on the one. I suspect you will find a higher maximum amp reading (from clamp-ammeter) since your battery-bank needing charging doubled in size.

A heavier gauge cable would add further improvement, but this can work for you. I used a second battery this way for a few years before trading for a trailer that had a 2-battery storage area.

Wow, as always, thanks to everybody for all this helpful info! Most of this stuff is a bit too technical for me, but I'm learning little by little.

To answer smkettner's question, if I were to purchase the PD4655 I would be adding a 2nd 24 series battery. About a week ago I tried a few days of dry camping and noticed I barely could make it through the day without draining my single 24 below 20%.

The 8-10 ft. run of 6 gauge cable is a one-way, positive-side, measurement only (from the battery to the converter). I kinda get the overall impression this setup will limit my maximum charge current (in 14.4 volt bulk mode) about 10-20% with this size/length of cable. Is this a reasonable assumption? Assuming it is, it doesn't seem like it's worth my time and effort to swap out this 8-10 ft. of 6 gauge cable (for a larger gauge) to save 30-45 minutes of charge time right now. If I get more serious about dry camping it may be something I may consider doing at a later time.

Right now, I believe my WFCO 8655 is giving me a 50% (12.2 volt) to 80-85% (12.6 volt) charge in approx. 4-5 hours. If I used my existing 8-10 ft. of 6 gauge cable with a PD 4655 would it be reasonable to expect this 50% to 80-85% charge time to be cut in half, to 2-3 hours?

Thanks!

RJsfishin wrote:
common sense tells most of us that after the first 5-10 minutes of charging, the amperage is a lot less, and less amperage requires smaller wire. Its as simple as that.

You are talking about limits on the current carrying capacity of the wire. That's not in issue. The OP has 6 gauge wire and a maximum current from his charger of 55A. That's within the ampacity specs for 6 gauge.

The OP wasn't asking if his wire was safe, he was asking if he'd get better performance with heavier wire, i.e., whether the small gauge wire "may limit the PD4655's charge current when it's in the 14.4 volt bulk mode". The answer is yes. 6 gauge does limit his charge current in bulk mode. Whether it's worth changing is up to him, but he will get better performance with shorter fatter wires.

The resistance of the charge cables has a critical effect on the charge current. That's why high end chargers come with remote voltage sensing capability - to avoid that critical effect. Unfortunately, his PD charger does not have remote voltage sensing capability.

Quote:

but the absolute current difference will be tiny once the "baseline" current is lower, so it is too small to matter to anybody. The difference you would notice would be in the beginning.


I don't see why you say that.
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The reason he says that, is because common sense tells most of us that after the first 5-10 minutes of charging, the amperage is a lot less, and less amperage requires smaller wire. Its as simple as that.Its the same as a smaller converter requires smaller wire. Anyone that can't figure that out, shouldn't be giving advice or answering questions, or even getting into the discussion!

BFL13 wrote:
Not sure if we are talking about the same thing but using the glass half full or half empty way of looking at it and getting mixed up.

:) perhaps - I'm not sure either.

The wire just adds some R to what the charger "sees" as the battery. So the thin wire makes it seem like the battery bank is smaller than it is (lower AH total capacity)

I agree that the additional resistance of the cabling is similar to the additional resistance of a smaller battery bank. If the charger is current limited however, the current will be the same no matter what the size of the bank - correct? No matter how big I make the bank, I get no more current, and as long as I don't make the bank so small that I leave the constant current regime, it will, by definition, remain in the maxed out constant current bulk charge mode.

This has the same effect as increasing the charging rate (initial charging amps wrt battery capacity)

Hmmmmm. I'm not sure I agree - (which also means I'm not necessarily disagreeing). The charging rate "(initial charging amps wrt battery capacity)" is the charge current compared to the capacity. Neither of those changes no matter how much resistance is in the cables, provided that we are in the initial bulk charging constant current mode.

which makes the battery reach Vabs at a lower SOC for same Vabs.

This - more or less - sounds like we agree. Yes, The absorption voltage Vabs is the max voltage for the charger. The charger reaches that voltage earlier when the cables have higher resistance. That's why I said that the effect of long thin high resistance comes at the end of the charge cycle - when the charger has left constant current mode. It leaves that mode earlier. From now on, the charger is running at fixed voltage (I'm assuming no remote voltage sense capability).

So amps will taper sooner in SOC,

Yes. With heavier shorter cables, you would still be in constant current mode, instead of tapering the current.

but you still get a faster charge in comparison with using a lower initial rate and a higher SOC where tapering starts.

I had to read that a few times, but I think I agree.

Once you are at the same SOC and battery voltage, the acceptance rate is the same and charging times will be the same from then on to fully charged.

I see what you are saying, and you are right, it's a glass half empty versus half full. I think you are saying that if we wait until the battery has reached the same SOC, the shape of the curve at the end of the charge cycle will be the same for both cases, so the effect of the high resistance cables shows up at the start. I'm saying that if we start two charge systems and batteries with the same SOC at the same start time and one differs from the other only by the resistance of the charge cables, they will have the same charge current at the beginning and the high resistance system will always be at a lower SOC and lower charge rate at the end (charge current started tapering earlier), so the difference is at the end of the charge cycle, not at the beginning.

Now you might say that since the thin wire makes the battery seem smaller than it really is, that you will take longer to charge it since it is bigger than it seems.

Yes. It takes longer to charge and the effect is seen after the constant current regime when both had the same constant current charging - the charge curve is shifted to the right (shifted in time).