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Old 07-14-2020, 01:44 AM   #1
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I've seen discussion about adding a 2nd alternator. I've also seen discussion about upgrading the stock alternator to a higher output one. What are the advantages/disadvantages of each?

What are the circumstances that would lead you to doing either?

Is there any rule regarding what output alternator[s] you have vs. battery capacity?

There seems to be some discussion on this list of 2nd alternator in lieu of solar panels. Advantages/disadvantages?

I hope I'm not asking too much but it's an interesting area for someone like myself who is considering upping battery capacity.

thx.glenn
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Old 07-14-2020, 02:32 AM   #2
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From discussions I've read here previously, it's far easier (and far cheaper) to upgrade your 145-160A current alternator to say a 225A model. An upgraded alternator would be plenty to push 60 amps of charge to your coach batteries. But perhaps while at or near the limit of the factory wiring back to your coach batteries (which is probably 4 ga.).

If you add a honking big second generator, you'd need to upgrade your wiring substantially. I currently push 40A from my standard 160A alternator which may be at it's limit. I see voltage drops at idle (only occassionally) when ac is on. No problem once engine speed gets above idle. My alternator has never seemed to get hot, unless that is what's happening at idle when perhaps it cuts back on output.

Adding a DC to DC charger is a cheap way to protect & limit the draw on your engine alternator, isolate the coach & engine batteries, and provide the right charge profile to your coach batteries (especially if they are a different type than your engine battery).
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Old 07-14-2020, 06:01 AM   #3
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We installed a second alternator in connection with our lithium house battery system in our DIY build. We saw two significant advantages. First, the second alternator can be a 'lithium-friendly' alternator specifically intended to charge lithium batteries (the second alternator in our installation has an external programmable regulator which we have set to suitable lithium parameters). The second advantage is that this second alternator can provide substantially higher charge currents than available from even an upgraded first alternator. We regularly charge at 150 amperes or higher (limiting the charge current only to limit alternator temperature during the summer months) - - fast charge rates being one of the advantages of lithium systems. Prior to lithium, we used the first alternator to charge our house battery (at rates of 30 amps or less).
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Old 07-14-2020, 06:11 AM   #4
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PS: We don't understand the concept of "2nd alternator in lieu of solar panels". We use both as they perform completely separate functions. When you're in motion - - use the alternator. When you're not, use solar. It might be argued that solar works both while in motion and stationary. True, but only when the sun is out, and not as 'fast' as an alternator. Go with both, have more flexibility.
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Old 07-14-2020, 12:50 PM   #5
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A second alternator advantages include those that Winston has stated, as in more amps to charge faster and ability to have it on a separate regulator for control. Another advantage is that they provide, mostly, a redundant charging source if the stock alternator dies. You do need to provide a way to connect it to the engine side, though, and it will do no good if the original alternator fails bearings and locks up or explodes.


For smaller battery banks up to the very typical 220ah or so setups in many vans, a single alternator gets more attractive, but IMO should be an improved size and quality one to give lower heat issues and increased reliability. A single 250-280 amp alternator will easily handle a 220ah bank, and last well if you limit the output to about 100 amps or less.


Our van was not computer controlled charging (2007) so I was able to put out second alternator in parallel with the OEM one which had already been replaced with bigger, improved, one. It gave us the ability to run very low % output for reliability and control them off one regulator. We can also just disconnect the coach batteries whenever the batteries get full without worry about damage to the electronics as the starting battery is still connected to alternators.


You likely would need to increase wire size with either a size upgrade or a standalone second alternator.


We have the lots of alternator charging, but also 300 watts of solar, and I would not go without the solar for the way we use the van. The solar is capable of keeping us offgrid, without driving, indefinitely if in good sun. The alternator charging sits in reserve so if we get bad weather or a shady site we can get a days worth of energy back into the batteries in about 20 minutes of driving.


We ran for a couple of years, during our testing of systems, with 260ah of Trojan wet cells, 300 watts of solar, and a single 250 amp alternator, and it did work very well for us, even with a compressor frig. Weak point was that the wet cells had trouble providing enough amps to run the microwave is they were less than full, so we had to idle the engine to run the microwave.
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Old 07-14-2020, 03:01 PM   #6
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Speaking for MB Sprinter owners upgrading your engine alternator probably doesn't give you much because you can only take off 40 amps for house purposes of charging house batteries. I don't know anything about Promasters or Chevys in that regard.

A second alternator like Nations or Delta (I've had both) charge your house batteries at up to 330 amps. Of course you need a wire coming off the second alternator to handle that. Mine is nearly 1/2" in diameter! With that kind of charging I can replenish my 800ah lithium battery bank in about 30 minutes of driving or idling for a day's stay in place boondocking with my all electric (no propane) van. I have 420 watts of solar but will not have any on my next van. Look at it this way. I am a profligate user of battery power at up to 200ah per day. My solar panels can charge my batteries at probably a maximum 120ah on a good sunny day. That is a losing situation. My second alternator can put that back in 30 minutes. Even if I stay in place at a boondocking campground for several days, I usually drive somewhere every day. Solar can never replenish my batteries. I store under cover when not in use, so solar in that regard is useless. I can think of other things to utilize on my roof like extra storage, skylights, decks, kayaks, etc.

I think if you have more than a 400ah battery bank solar contribution is negligible for the return and you probably should have a second alternator. If you have under 200ah as most Class B RVs do it can make a significant contribution but then a second alternator is a waste of money.

BTW, this is what 420 watts of solar looks like in 3 panel on an extended van Sprinter of 24 foot. If I had less, my comparison numbers would be worse. That's why I am going no solar on my next van.

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Old 07-14-2020, 11:14 PM   #7
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Quote:
Originally Posted by Davydd View Post
I am a profligate user of battery power at up to 200ah per day. My solar panels can charge my batteries at probably a maximum 120ah on a good sunny day.
We, too, are a "profligate user of battery power" and would love to use our roof space for kayaks etc. But we like the diversity of having multiple charging sources. While we designed our system to allow 'idling' to charge our batteries, we aren't a fan of this approach and would rather have solar do that job when parked for several days.

This summer has been interesting for solar. We spent more time, further south, than usual. Couple that with higher altitude, cooler temperatures and bracketing the summer solstice and we 'smashed' our prior solar 'collection' records. Our max was, two days in a row, 5.3 kwhs with many days over 5 kwh/day (which equates to 408ah/day). And this just about met our "profligate" electrical energy consumption!

So guess we'll have to consider 'blow-up' kayaks - - as we're gonna keep the solar.
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Old 07-14-2020, 11:27 PM   #8
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First define how many/much battery you are going to add. With one additional battery even an upgraded primary alternator is not necessary. If it is lithium then a DC to DC charger is needed.

Install the battery or batteries then decide on charging options.
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Old 07-14-2020, 11:38 PM   #9
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I understand the desire to have multiple means. But I do have a question relating to solar. If you are parked, say, in the shade of trees, how much solar is harvested? Being from the SouthWest and camping almost exclusively in the SW we would never camp in the sun unless there was no other choice. So I am curious about the advantage to having solar but camping always in the shade.
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Old 07-14-2020, 11:43 PM   #10
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I understand the desire to have multiple means. But I do have a question relating to solar. If you are parked, say, in the shade of trees, how much solar is harvested? Being from the SouthWest and camping almost exclusively in the SW we would never camp in the sun unless there was no other choice. So I am curious about the advantage to having solar but camping always in the shade.

It has a lot to do with how deep the shade is and if it is all day or partial, plus is you are series or parallel wired.


It is very easy to have ours go to 1/2 or considerably less in deep shade. In cloudly, drizzly foggy weather seen in do only 10-20% of our good sun harvesting.
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