Cable Requirements for PD4655 Converter

I still want to know if OP is charging a single walmart 24 or four+ Lifeline 8D.

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.

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)

This has the same effect as increasing the charging rate (initial charging amps wrt battery capacity) which makes the battery reach Vabs at a lower SOC for same Vabs. So amps will taper sooner in SOC, but you still get a faster charge in comparison with using a lower initial rate and a higher SOC where tapering starts.

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.

Sorry, I have to show this with my ugly graph again, since it is too hard to describe in text:



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.

BFL13 wrote:
If the wire is too long/thin then current will be less than it could be from start to finish,

It depends somewhat on whether we are discussing the quirks of different chargers or the preferred charge profiles. The typical charger is designed to provide constant current during bulk mode charging. It will increase its voltage until it either reaches its maximum designed voltage, or its maximum designed current limit. For a charger designed that way, the charger can't tell the difference between a long thin wire leading to a discharged battery (low SOC) and a fat thick one leading to one of higher SOC, provided that both batteries are sufficiently discharged that the sum of the voltage drop on the cables plus the battery voltage at that SOC is low enough that the charger is in the bulk mode. The charger will just increase its voltage to compensate for any voltage drop on the wires, no matter how thin or long. As long as the charger doesn't run into its voltage limit, the wire diameter/length won't have any effect.

The effect arises when the charger does run into its voltage limit. That happens sooner with the long thin high resistance cables at the end of the charge cycle.

That's for the idealized design charger.

The PD doesn't always follow that perfect charge profile. I've tested my PD9280, both before I modified it and after. Provided you give it a decent AC voltage to work with, mine is pretty close to the idealization described above. It tends to climb in current for while (about 6% up in my tests), then taper about the same % down before it leaves bulk mode.

If you do not give it sufficient AC voltage, then the PD has a tendency to taper early.

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. The output of the charger depends on the voltage it sees at its output terminals. That's equal to the voltage drop of the cables plus the voltage of the battery. The purpose of short and fat is to decrease the voltage drop over the charge cables so that the charger stays in current limited bulk mode longer (and wastes less power in the cables).

The PD tapers anyway at the 14.4 stage, so you might not notice anything better even if you did go from #6 to say #4.

In my tests, that only happens at lower AC voltages. At higher voltages, it actually boosts for a while, then tapers.

IMO try it out as is and see if that is good enough for your needs. Then decide if it is "worth it" to change the wire to get five or ten minutes reduction in gen time to do a 50-90.

That seems like a reasonable difference, but the difference will increase if he decides he needs to go from 75 to 95. In a sense, we are in agreement. The lower the SOC, the more likely it is the charger will be current limited, not voltage limited, and when current limited, it doesn't make any difference how long/thin your wires are, except that you'll be wasting some energy heating them. Only when the charger has entered the voltage limited region do the wires matter.

Of course, none of the chargers being sold follow the perfect charge profile.

DryCamper11 wrote:

RJsfishin wrote:
Its not worth changing wire. If you loose anything, it will be for only the first 5 or 10 minutes while the converter is putting out max current. After several minutes, the current will taper, and will then be well w/ in the current range of 6 ga wire. I ran a PD9155 on 6 ga for many years.
Just make sure you get the optional remote Pendant control w/ it.

I disagree. The problem is not at the beginning. Current is current, so if the charger is putting out max current, that current is going into the battery. The charge current produces a voltage drop on the cables, and the longer thinner they are, the more that voltage drop is. As long as the sum of that voltage drop and the battery voltage is below the maximum charger voltage, you'll get maximum current.

The problem with long thin wires occurs at the end of the charge cycle, not the beginning.

(I definitely agree that you should get the pendant. It's one of the main reasons why I bought a PD and not an Iota.)

I think RJ is more correct on that. I think the above is talking about two different things but it is hard to tell.

If the wire is too long/thin then current will be less than it could be from start to finish, 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.

The PD tapers anyway at the 14.4 stage, so you might not notice anything better even if you did go from #6 to say #4. IMO try it out as is and see if that is good enough for your needs. Then decide if it is "worth it" to change the wire to get five or ten minutes reduction in gen time to do a 50-90.

Don't forget the diminishing returns you get by raising the charging rate when deciding what is "worth it" My old ugly graph of the 70/55/35a chargers on a 220a bank that I inflict on the forum every so often shows that clearly.

otrfun wrote:
too small gauge of cable (for the run length) and may limit the PD4655's charge current when it's in the 14.4 volt bulk mode.
True? False?

True. You can't get cables that are too thick. There's always a compromise. I chose 1/0 welding cable (buy from the local welding store) for the reasons set forth above, but think about your needs. If you don't need maximum rate charging at the end, because you normally are plugged in or have solar, your cables may be fine.

RJsfishin wrote:
Its not worth changing wire. If you loose anything, it will be for only the first 5 or 10 minutes while the converter is putting out max current. After several minutes, the current will taper, and will then be well w/ in the current range of 6 ga wire. I ran a PD9155 on 6 ga for many years.
Just make sure you get the optional remote Pendant control w/ it.

I disagree. The problem is not at the beginning. Current is current, so if the charger is putting out max current, that current is going into the battery. The charge current produces a voltage drop on the cables, and the longer thinner they are, the more that voltage drop is. As long as the sum of that voltage drop and the battery voltage is below the maximum charger voltage, you'll get maximum current.

The problem with long thin wires occurs at the end of the charge cycle, not the beginning.

(I definitely agree that you should get the pendant. It's one of the main reasons why I bought a PD and not an Iota.)

I used 1/0 cable and moved my PD9280 to within 3' of the batteries. 1/0 is the largest wire that will fit the dual terminals of the PD9280 when you split it into two bundles and feed both into the terminal pair at the PD9280 output (one pair is provided for positive and one pair for negative).

When you start charging below about 80% state of charge, you should get the full amperage output of your charger. If the cable is small, there will be some voltage drop, so the charger will see the battery voltage plus the voltage drop on the cable and think that's the battery voltage. It's no problem at this point because the charger will simply increase the amperage up to its limit as long as the sum of the cable voltage drop plus the battery voltage is below the charger output voltage.

However, as the battery voltage rises, there will come a point where the sum of those two is equal to the output voltage of the charger. Now the charger can't increase its output voltage any more, so it begins cutting back the charge current. The longer your charge cables, and the thinner they are, the sooner this cutback happens. You now face longer charge times, since the charge current is reduced.

Some people don't care. They are plugged in 24 hours. Others have solar and don't have high charge rates anyway. But if you are boondocking and need to charge with a gen, as I do, this decreased rate is a real problem. There are two solutions. One is to buy a remote sensing charger. It will sense the true battery voltage, not the battery voltage plus the voltage drop through the cables. This is an excellent solution, but can be expensive. The other solution is to reduce the resistance of the cables. Short and fat is a simple solution if you can get it to work for you. I would have used 4/0 charge cables if they would have fit. :)

Its not worth changing wire. If you loose anything, it will be for only the first 5 or 10 minutes while the converter is putting out max current. After several minutes, the current will taper, and will then be well w/ in the current range of 6 ga wire. I ran a PD9155 on 6 ga for many years.
Just make sure you get the optional remote Pendant control w/ it.

I supplemented my WFCO converter with a deck-mount IOTA-55. To keep the battery leads as short as possible I mounted the IOTA in the front pass-through compartment, giving me a 3' run to the batteries. For AC power I tapped off an outlet by the bed and ran it to a switched outlet I mounted in the pass-through.
There was a spare circuit breaker slot in the WFCO. The parts bin yielded a compatible breaker so I put the WFCO on its own circuit so it can be switched on or off.

If it's easy, go with #4 welding cable easy to get, reasonably priced, and run the negative to the frame rather than a long run to the battery.

And if I remember correctly, #4 is the biggest dia wire you can get into the PD lugs.

#6 of that length will limit the current somewhat, and likely have it drop out of constant current a bit early. However if it is difficult to change, I'd at least start with the #6 and see what happens. I think you'll still see way better results than the WFCO.

How much it affects charging is noticeably dependent on what kind and how many batteries you have. Based on my previous experiece with wire size and PD converter, the #6 will likely get you in the 50A range, and #4 closer to the full 55A range if the batteries are discharged enough.

If you were looking at the 60A or 80A unit, another story, then you would need to upgrade the wiring.