Simplest way to charge lithium with solar+alternator

[Sprinterino]

Hey yall, first-time camper van converters here building our Sprinter into our new home and looking for advice on the best or simplest way to charge 200Ah lithium iron phosphate batteries from a mix of about 400w solar and alternator charging. I'm guessing we should get a second alternator to charge the batteries, or is there a simpler way? Thanks for any help!

 

[Sprinterino]

Or if we bought AGM batteries would they charge more simply directly from the alternator with needing to adjust the voltage?

 

[Van-Tramp]

No reason for a second alternator at all.

My van has lithium as a house battery and lead acid as a starter battery. Both are charged by both solar and alternator simply by using a battery combiner ( I use this one https://amzn.to/2JYKy61 ) between the two batteries.

 

[Ticklebellly]

Dual Input (Alternator and solar) DC to DC charger is taking care of my LiFePo4. My DC to DC has inbuilt isolator and MPPT controller. Also charges to 14.1 then turns off. Have not had to do a top balance in 14 months. Setup fits my adherence to the KISS principal.

 

[Sprinterino]

Thanks for the advice. I had seen on many videos that people say the standard alternator doesn't run on the same voltage as a lithium battery which would cause excess wear on the battery and alternator causing premature fail so they used a second alternator instead. The battery combiner seems like a much simpler solution, thanks! Tickle could you link me to your DC to DC by any chance? Thanks guys!

 

[Ticklebellly]

There are a couple of useful threads discussing pros and cons of Alternator direct charging, worth reading. The DC to DC charger I have is no longer available. I suggest you Google DC to DC chargers for Lithium and concentrate on the ones that charge in one step then turn off rather than go to FLoat. Lead Acid benefits from multi stage charging, LiFePo4 does not need it.

 

[LoupGarou]

Goal Zero nailed it with a vehicle charger for their Yeti lithium power stations with a built in isolator.

 

[MrAlvinDude]

Please note that "lithium iron phosphate" (LPF or LiFePO4) and "lithium phosphate" (Li-Po) batteries are NOT the same kind of batteries! And they have (significant) different voltage limitations.

Sometimes the same reference name "lithium batteries" are used. I would recommend that you do Not chose to do that, as LIFePO4 and Li-Po batteries NEEDs to be handled, managed and charged in very different ways. Likewise the charge (and discharge) rate  (C-ratings) of both LPF and Li-Po batteries can be Very different between different battery products. 
So specification limits (Volt and Amp limits) should always be investigated, and known, for each brand and model of lithium based batteries. 

"lithium iron phosphate" (LPF or LiFePO4) 12V batteries, for instance, have voltage limits that are almost similar to 12V Lead Acid batteries, so in some (/many) applications it is possible to use them as drop-in replacements.

This is NOT the case for "12V" Li-Po based batteries - if such a thing even exists. 


If you want your 12V LFP batteries to live as long as possible, then it is wise to pay attention to, and choose your own, "best practices"  about voltage limits.  


And possibly invest in a battery monitor that can see the voltage condition of each cell in the 12V LPF battery (if this is not already built-into the battery).

 

[Ticklebellly]

...... the best or simplest way to charge 200Ah lithium iron phosphate batteries from a mix of about 400w solar and alternator charging. 

My reply was specific to LiFePo4 and acknowledges a Greenfield build using that technology.

The DC to DC charger I mentioned has a setting for Li Ion batteries.   I use Li Ion to power an electric outboard, an electric bike, and a DIY conversion Quad.

I have had a couple of friends do the "drop in".   Best success was with a legacy D250S, commercial offering Battery with integral BMS, and Bluethooth monitoring so the charger would be disconnected once the battery was charged.   This charge and stop idea is built in to my current DC to DC charger.   The Multi-step charging from the D250S does not seem to have caused problems in that Drop In conversion system over the last 2 years.

My judgement of the Goal Zero offering is that you pay waaaaaay too much for not very much.

Alternator charging, using a battery connection device, seems to work OK if the battery being charged has an integral BMS that includes battery specific charge control and limits.   I use a DC to DC charger to a battery constructed from discrete cells and with cell mounted top balance boards.

Not sure the original question to the thread has been answered simply.

 

[Ticklebellly]

This is NOT the case for "12V" Li-Po based batteries - if such a thing even exists. 

An eBay search shows that there are lots of offerings.   I run a Wildlife spotting light off one.   The battery came with a 12.6 volt charger with a simple LED indicator to show if charging is active.   No Name brand but 7 AH and was cheap enough to experiment with.

 

[Sprinterino]

Thanks very much for the replies!

 

[IGBT]

My judgement of the Goal Zero offering is that you pay waaaaaay too much for not very much.

Actually their Yeti 3000 with mppt solar charger, 1500 watt pure sine inverter and 3kw-h of lithium manganese was a pretty good deal this weekend at $2250.

In some ways it is not as good as LiFePO4 (longevity) but it has a higher energy density so is lighter.  The whole thing is 67 pounds which is about the weight of one group 31 lead acid.

I think battleborn batteries are about $900 or so for around 1kWh.  Raw cells of LiFePO4 would be about $1200 for 3kWh, and that is with no charger or bms or duct tape.

 

[Sprinterino]

So I am currently looking at the REDARC BCDC1250D it is a 50A Dual Input DC to DC Charger. Is this a good product? Also, if I want to charge from the grid how would I do that? Would I need another product? And will this charger charge from both solar and alternator at the same time or only one at a time? It's unclear on the site. Thanks

 

[Sprinterino]

So I have read about BMS systems being an all-in-one that can also charge from grid. Can anyone recommend a good BMS for North American use? Thanks!

 

[Ticklebellly]

....... so they used a second alternator instead. 

Discussing direct charging with a fellow user of Li, and he asked if there might be any issue caused by too high a charge rate.    Li typically accept what ever you can put to them.   I'm thinking of the scenario where a small capacity Li (say 40 AH) is attached to a high capacity alternator.   Extreme conditions like Li at under 12 volts and an Alternator putting out 14.3, what charge current will be going into the Li?    I don't know the answer and did not have to consider the situation because I use a DC to DC charger.   I don't see discussion of the scenario I put is relevent here but maybe others putting in a Li install from scratch should think about it.

 

[Sprinterino]

It's an interesting question. Most places I read recommend Lithium for the benefits, but my battery guy says it's not worth the price and tells me to go AGM, so I'm gonna hash it out with him today before I make a decision.