Which Charges Faster?

[markopolo]

Originally Posted by JamsRN

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Anyone see an issue with this? My goal is when I’m boondocking to be able to sleep with the Dometic Penguin II AC on. Plan to have 600 ah of Lithium batteries, 600 watts of solar on the roof, a 3000 watt Victron Pure Sine inverter/charger and 60a DC-DC charger.

Trying to ditch the generator.

You really should look into adding a second alternator.

If you're going to spend that much then it means that you probably plan to use it often & that's going to result in a lot of alternator run time.

If you're parked in a shady spot and want to stay there but down say 480Ah that's 8 hours of idling the van to recover the 480Ah using a 60A DC-DC charger so you can run the A/C at night again and that doesn't include the daytime use!

& great point by Jake re: SOC trigger vs voltage trigger

[booster]

Originally Posted by markopolo

You really should look into adding a second alternator.

If you're going to spend that much then it means that you probably plan to use it often & that's going to result in a lot of alternator run time.

If you're parked in a shady spot and want to stay there but down say 480Ah that's 8 hours of idling the van to recover the 480Ah using a 60A DC-DC charger so you can run the A/C at night again and that doesn't include the daytime use!

& great point by Jake re: SOC trigger vs voltage trigger

The solar will probably give a bit under 200ah of recovery in very good conditions in one day and overnight is going to take probably 3 times that if the AC runs a normal amount, so probable 400ah short of recovery assuming no other use of power. Run the AC at all during the day and would need lots more.



A second alternator will net about 165 amps so probably around 3 hours of run time for it to need to run, if it will do that much at idle.



I don't think I would want to subject a stock alternator to that much charging all the time and agree with Marko it probably would require an awful lot of running the engine.


We have had lots of discussions about using batteries for AC, and most would indicate it isn't easy or cheap to do because of the issues of recovering the energy used.



If starting from scratch on it, this might a time to consider using 36 volt system or some other higher than 12 volts. It would reduce the current and probably increase the available charging watts from the second alternator compared to a 12v one. Cost wouldn't be all that much different, I think.


I completely agree with using a monitor and SOC trigger instead of voltage.

[Winston]

Originally Posted by booster

A second alternator will net about 165 amps so probably around 3 hours of run time for it to need to run, if it will do that much at idle.

If starting from scratch on it, this might a time to consider using 36 volt system or some other higher than 12 volts. It would reduce the current and probably increase the available charging watts from the second alternator compared to a 12v one. Cost wouldn't be all that much different, I think.

A cautionary word concerning alternators - Temperature.

We have a Nations 280amp 2nd alternator which is currently set to provide between 150-175 amps when our lithium pack is moderately-to-significantly discharged - - with that charging rate decreasing fairly rapidly (<1 hour) to 75 amperes.

If we have a 280 amp alternator, why do we have it set so low? - Temperature.

During hot summer days we cannot 'idle' and charge for more than about 5 minutes before the alternator temperature exceeds our target level of 102 degrees C. The ambient temperature has to drop below (at least) 60 degrees (F) before we can continuously idle and charge our pack.

We can, however, in any ambient temperature, continuously run our 2nd alternator (at the above-noted setting) while driving as there appears to be sufficient air flow to cool the alternator. (We have a ProMaster with the notorious 'low-slung' 2nd alternator.)

Thus we think Booster makes an important point - - running higher voltage with a correspondingly lower current will eliminate these temperature restrictions.

[booster]

Originally Posted by Winston

A cautionary word concerning alternators - Temperature.

We have a Nations 280amp 2nd alternator which is currently set to provide between 150-175 amps when our lithium pack is moderately-to-significantly discharged - - with that charging rate decreasing fairly rapidly (<1 hour) to 75 amperes.

If we have a 280 amp alternator, why do we have it set so low? - Temperature.

During hot summer days we cannot 'idle' and charge for more than about 5 minutes before the alternator temperature exceeds our target level of 102 degrees C. The ambient temperature has to drop below (at least) 60 degrees (F) before we can continuously idle and charge our pack.

We can, however, in any ambient temperature, continuously run our 2nd alternator (at the above-noted setting) while driving as there appears to be sufficient air flow to cool the alternator. (We have a ProMaster with the notorious 'low-slung' 2nd alternator.)

Thus we think Booster makes an important point - - running higher voltage with a correspondingly lower current will eliminate these temperature restrictions.

I am a not surprised that you have to stay that low and/or cool weather to run continuous, but it isn't all that far off the 165* approx average folks have seen with a cycling Nations off the Balmar heat ceiling of about 225*(?). Where are you reading the temps? I found that the laminations were hottest spot on our two Nations/DC Power units.


What you see is why we put our alternators in parallel. Our 07 Chevy was among the last that still had a system in it that allowed it without issues. We have a 250 and a 280 amp and if idling we would get both of them up to 225*, if we charged at about 280 amps (probably a bit over 300 amps total), in about 20 minutes. Of course our AGMs would also start to get hot about the same time, so no big deal for a quick recover charge. But, we never needed it that high so I turned it down to 180 amps on the high output setting and 120 amps on the lower setting (our external regulator allows for switchable field current max). We can run either of those without overheating the alternators or the batteries.


If I were to do the system now, it would be at least 24 volts to reduce heat. The only downside would be finding a place to hide the B to B charger we would need to run the coach 12v. The rest would be pretty much the same parts in an alternate voltage.