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Old 10-19-2018, 11:20 AM   #1
Join Date: Dec 2017
Location: ND
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Solar question

Is there a way to connect your solar system to you car so when you are driving it charges your solar batteries

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Old 10-19-2018, 11:36 AM   #2
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From what I have read, you can charge the batteries off a second or high-output alternator. I think this is an acceptable method for Li batteries, but I think I read something about this not being a great option for lead acid batteries. Perhaps somebody with more knowledge on this will stop by.
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Old 10-19-2018, 12:27 PM   #3
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A couple things:

1. ELectricity travels from higher voltage to lower voltage. if your solar system is pushing 14.8v and your alternator is pushing 14.0, your solar charger will be sending power to your alternator. It almost surely has a diode, but ultimately it won't be doing what you hoped it would do.

2. Storage batteries often charge to higher voltages than start batteries. An AGM battery probably charges at 14.8v, and bus alternators tend to push 14.0 or less... Meaning you'll never fill your batteries without having a separate charging converter to boost it's voltage. Your start battery likely charges to full around 13v so without splitting the circuits you can expect your AGM will be sending power to the start battery, which will cook it.
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Old 10-19-2018, 12:43 PM   #4
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I saw this article where a guy in his own camper van used this battery charger to charge his batteries off his alternator. I've been considering it, but am curious if anyone knows whether this is a) a good option and b) any reason it wouldn't work on a bus?
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Old 10-19-2018, 01:28 PM   #5
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You have solar panels on your car?
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Old 10-19-2018, 02:25 PM   #6
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As soon as the voltage of your solar battery bank is higher than the voltage of your car/bus, you will need a "DC-DC boost converter". If you search ebay with this term, you'll find plenty of options.

Either the boost converter or the charge controller has to limit the current to what the converter can safely handle since a large battery bank can draw a much higher charging current.

The DC-DC conversion from your car alternator voltage to the battery bank voltage is not the most efficient approach but who cares if the whole system is driven by a huge and inefficient internal combustion engine.
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Old 10-19-2018, 03:53 PM   #7
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In both our buses we have the house and starter battery are the same. The solar and alternator are just tied together. The lack of a three stage charger algorithm in the alternator is in my point of view not a big deal since it is used relatively little. The alternator has a pretty large current output so that leaves the alternator as the bulk charger. Many alternators can be modified with an adjustable regulator if so desired.
The three stage charger algorithm for lead acid chemistry are kind of prehistoric because there were no proper ways to determine the amount of AH taken out of he battery versus the AH put back in. The float battery charge is essentially a waste of energy because nobody knows exactly where the lead acid battery charge level is so they just give it that little extra charge that gets converted in heat and potential of gassing.

In Forklift batteries that are pretty tall this "boiling" or better bubbling was used to stir the battery acid as to avoid stratification but I think charging with a AH in AH is a better more efficient way.

Like Alpine mentioned , if you want to charge via the charge controller then an DC DC converter can do the job. If you use a mppt controller then be sure that your DC/ Dc converter / alternator combo is more powerful then your MPPT controller so that the MPPT can not overload your DC DC / alternator combo.

Later J
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batteries, bus, solar, solar power

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