[split] charging my Li battery

[DanDweller]

I guess I'll just try re-typing the whole question and post here in parts.  This is so strange.

Hello all, I am about to convert my Ford Transit Connect 2015 XL for vandwelling and am looking at how to charge the 100ah lithium iron phosphate battery which I will use to power vent-fan and lights.  In addition to solar panels, I also want the option to charge from the alternator.  What I learned from talking to a technician at Renogy is that a DC to DC charger with MPPT will control both options.  But the one they sell draws 50 amps from the alternator and he advised me to find out if my alternator can handle the additional draw.  Calling Ford and Ford dealers has been fruitless.

(I'll post the rest of the question after seeing if it allows this.)

 

[DanDweller]

Miracle! Okay, here goes the rest:

I bet 50 amps is too much draw from the alternator (and more than I need), but I don't really understand these things so well. Can someone please help me out here, or recommend another brand of a similar DC to DC battery charger with MPPT but which draws a lower, more acceptable, amperage from the alternator (how many would be safe?) allowing to charge via altrrnator or solar panels, and which would work with the Renogy lithium iron phosphate battery?

Also, I would like to have an inverter charger for a shore power option, but the smallest one Renogy sells is 2000 watts--much more than I will need. (I would only occasionally use the inverter to charge my electric shaver and use a laptop.) Is there another brand someone could recommend, and which is for lithium iron phosphate batteries?

Thank you!

 

[AuricTech]

Which engine does your vehicle have?

With that information, you should be able to find out the capacity of your stock alternator. You might also be able to find a more powerful aftermarket alternator at an auto parts store.

 

[DanDweller]

Which engine does your vehicle have?

With that information, you should be able to find out the capacity of your stock alternator. You might also be able to find a more powerful aftermarket alternator at an auto parts store.

It's the 2.5L, 4cyl.  But I'm actually starting to lean toward ditching the idea of connecting the house energy system to the alternator at all.  Just solar panels and shore power.  Reading around the forums, it seems like most people are doing that, no problem.  Seems a lot simpler.

 

[highdesertranger]

Dan I split the thread off for you. I will delete the other thread and I will PM you. highdesertranger

 

[Cajunwolf]

Try this. Go to a local starter/alternator shop and see if they can build up your alternator to handle the additional load, or see if he can perhaps suggest, or have one that will work for a reasonable price. An alternator is nothing more than a three-phase AC generator with a rectifier and voltage regulator. Often, a change of voltage regulator is all one needs.

 

[Matlock]

Charging a battery with the vehicle alternator will require a daily drive of some distance. Cost of fuel may help decide on a different option.
If you do go with a larger alternator be sure to look at resizing the existing pulley and belt and also ask about the wire size. You don't want to fry anything under the hood so lastly make sure you have plenty of air-flow to keep that alternator cool. Nothing kills voltage regulators quicker than too much heat.

just my 2¢

 

[MrAlvinDude]

hmmm...  I wonder if you are aware that the charge rate of a battery (how many amp goes into the battery while it is being charged) is ALWAYS directly dependent on the voltage difference between the voltage of the charge power source and the actual voltage of the battery?

So what you need is a charger that can adjust its output voltage, to match a pre-set max amp charge rate.


This all follows from Ohm's law, as we are dealing with DC volt, current  and resistance.

Ohm's law states that U = R * I 

and in this case
U = volt difference,
R = internal battery resistance
I = the desired max amp charge rate.

The internal resistance of the battery is beyond our control, as it is being dictated by the internal chemistry of the battery.
We have locked down the Amp setting.
So the only parameter left, is the voltage difference. And we can not deside the voltage of the battery (as this is a result of the state of the internal chemistry of the battery), but we can control the output voltage of the charger. And thus this becomes our tool with which we can control how many amps are being allowed to flow through the system.


And this is why I say, that you need a battery charger that can control its output voltage, to match a pre-set max amp charge rate.


I suppose it is not yet common to find off-the-shelf battery chargers, where one can set the max charge rate, because it is usually desirable to simply charge as fast as possible.
But someone on this forum might know of such a battery charger.  


So, as I see it,
you can choose to optimize each component in your charge system, to be able to charge as fast as possible.  And your alternator seems to be the bottle neck in you current setup. 
 
Or you can look for a battery charger device where it is possible to set the max amp charge rate

It might also be possible to find a smart charger that, in order to protect it self, will not allow charging faster than 10 or 20 amp, even if the alternator and the battery could manage faster charge rates.

 

[Cajunwolf]

@MrAlvinDude
Excellent and very educational, thanks for the effort!