Powermax PM3 vs PM4 decision

[hikerboy1]

Looking to replace the main board assembly on my WFCO8955 converter that is less than speedy at recharging a pair of new group 24 deep cycle batteries. Interested in the Powermax, and I see that they offer the PM3 and the PM4....only difference seems to be the extra "desulfate" mode on the PM4; both are advertised as direct replacements for the WFCO MBA unit. Any first hand experience with either? I know that the WFCO is resistant to higher charging voltages, but searching the forum here leads me to believe that the Powermax is much better at the task. We dry camp a lot, and use a Honda 2000 genny. The PM3 main board assembly is a fair amount less expensive. Thanks for the thoughts!

[BFL13]

It depends a lot on whether you run the gen to do 50-80s or 50-90s. The 80-90 part really adds to your gen time.

When (what SOC) your batteries get up to at the 14.6 threshold depends on the charging rate, so then you need to look at how much more in SOC you will be doing at the lower 13.6 absorption voltage before you get to your target SOC

55amps on two 24s (160AH?) is 55/160= 34% charging rate, which is the highest you would want to go in any case. That will get you to 14.6, if you start at 50% SOC, by 66% SOC. You would do the 66 on up at the 13.6.

45 amps on 160 is a 28% charging rate that will get you to 14.6 approx. at 70% SOC so you would need to do the 70-80 at 13.6 if doing a 50-80. But how much more gen time is that compared with staying at 14.6?

66-80 is 14% SOC or 23AH of 160. If you were still doing 55amps at 14.6 that would take about 30 minutes. If you got half that many amps at 13.6 it would take an hour.

Say you swap out the two 24s (160AH)for a pair of 6s (220AH) (same footprint but taller) and go with the 55 amper. Now your charging rate is 55/220 = 25% and you will hit 14.6 at 72%, leaving 8% to do at the 13.6 doing a 50-80.

One thing with the PD is that it can be slower in bulk doing the 50-70 part due to some amps tapering in there comnpared with the PowerMax, you can keep its voltage up for that 70-80 part using the Charge Wizard. So the PD could be a bit faster overall, especially if you go higher in SOC before stopping the gen where more of the recharge is beyond that 70% point.

If you camp such that your batts are near 50% in the morning and you normally do an hour of generator in the morning and then go onto solar the rest of the day, then that hour of gen time is all in the 50-70 part where the PowerMax is in bulk doing max rated amps. In that scenario, you don't care if it will drop back to 13.6 if you did more of the recharge by gen that day instead of by solar.

[time2roll]

PM converter does not hold the high boost voltage but drops immediately to normal mode once 14.6 is reached at the converter. The higher the amps the lower the battery state of charge when this shift occurs. My preference would be to let the voltage climb a bit slower to get more energy in the battery before it essentially quits. A longer or thinner charging wire will exasperate the issue.

[BFL13]

A Honda 2000 can easily handle a 55 amper. Eco has nothing to do with that as such, it just revs up if the load is higher. But when starting cold, it is a good idea to start with Eco off so it doesn't conk out with the load on it, then after it is warmed up in a few minutes, then turn Eco on.

[hikerboy1]

I was leaning towards the PM4, and am wondering if I need the 55 amp version or could get by fine with the 45 amp version. 22' trailer, 2-way refrigerator, furnace, shur-flo, and a few light bulbs would likely be the most it would ever need to support. Maybe the 55 amp would be a safer bet, but probably a little more taxing on the Honda 2000 genny when charging in eco mode?

[BFL13]

My older PM3 (but newer than an original PM) has the three stages, not four, but has the same thing as a WFCO for going into boost, which is that the batteries must be low, around 50% or less. Otherwise it stays at 13.6.

Some time or other, they changed this to be more like an Iota so it goes into boost every time no matter what the battery SOC and stays there for 15 minutes, then if the batteries are already near full it will drop to 13.6 or else if not near full stay at 14.4 until battery voltage reaches 14.4 and then it will drop to 13.6

I never found out if that was "later" PM3s or only the newer PM4s, but for sure the PM4 is the new way, not like a WFCO.

A curious feature is that Randy at bestconverters.com has his own version of a PM4, which he calls a Boondocker, that goes to 14.6 instead of 14.4 but is otherwise a PM4.

To be sure to get the four stages, the 14.6, and the Iota boost start way, go with a Boondocker. Ask Randy pointed questions about all these things. He knows.

I can't figure out what those "PM3s" are that boatandrv sells, that they call PM3s but claim to be four stage like a PM4. You would have to ask them if it does the WFCO thing or the Iota thing. They might not even know about that, no idea.

[time2roll]

35 amp or 45 amp PM4B would be my choice.