LiFeP04 charge controller recommendations

ducktapeguy

Adventurer
Need recommendations for a new charge controller/dc battery charger.

Right now my current setup is a deep cycle battery charging from the alternator through a relay when the engine is on, then switches over to 100W solar using a Renogy 10A charge controller. This has been working fine for a year or two. I just upgraded my aux battery from a deep cycle to a 100Ah Renogy lithium iron and from my reading it sounds like I need to reconfigure my setup.

Questions

1. Will the LiFe charge straight from the alternator? I am reading differing opinions on this, some say its fine but the battery will not charge fully, other say it's not safe for the battery. If it can, then all I need to do is replace my solar charge controller with a lithium compatible one and I'm good.
2. If I can't connect direct to alternator, do I need a separate dc/dc charger when using alternator power? It doesn't sound like newer alternators put out enough voltage to effectively charge the battery through the charge controller, so I'd have to isolate the two power sources and have a different controller for each
3. Ideally I'm looking for one controller than can do both. I think the Renogy Voyager 20A should be able to handle the solar part, not sure about the alternator side of it. The Victron Smart Solar MPPT also sounds like it would work, but might be overkill for my needs. 20A charging is more than enough for my needs. One thing about the Victron is I'm not sure if they have the right charge profile for lithium, or maybe I'm just not understanding the datasheets correctly.
 
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Swiftone

Member
I had somewhat of the same situation. Son has a 1998 Cherokee that we mounted a 100 Watt panel, run thru a smaller Victron controller/20AH Bioenno/Dometic compressor fridge. He is a Type 1 diabetic/swimmer and he keeps his food in there. Worked great in the California sun...not so well in the Ca winter.

Dreadlocks (and I hope he does not mind I am sharing this) offered up this suggestion:

If it were me, I'd pickup a Victron 15A, a small 12VDC dpdt relay, and a small 12v to 24v converter.. hook the converter up to a keyed vehicle source, wire the solar panel to the NC ports on relay, and the converter to the NO ports on relay.. then power that relay by a keyed ignition source.

When you turn the engine on, it will disconnect the solar panel and hookup the 24v converter.. the MPPT controller will be tuned to your charge params and convert it down to whatever voltage it needs.. then when you shut engine off, it'll hook the solar back up to the MPPT and let it finish/maintain it.


That worked like a champ! He is at school right now so no pictures, but here one of the panel on his jeep. The big advantage is the always temperamental Jeep electrical system is keep separate from the aux power.

 
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john61ct

Adventurer
Charge controller usually just means solar.

From the alt called a DC-DC charger.

From shore power or genset, called a mains charger or AC-DC charger.

A DC-DC charger can be used to precisely charge according to the desired profile

from a crappy mains charger or solar controller.

I like Sterling's BB series best myself, you def want user custom setpoint adjustability.

Some say the Victron SmartSolar units can act as a general DCDC, but I haven't verified that myself.
 
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pugslyyy

Expedition Vehicle Engineer Guy
You use a DC-to-DC charger to protect the vehicle charging system and wiring, not the house battery. If you don't have something to restrict the amount of power the lithium battery is pulling it will run your alternator at 100% (or higher) rated output.

On an older vehicle it's not a huge deal - you might shorten the life of that 120A alternator, but for a modern vehicle with almost 400 Amps of alternator output you can seriously overwhelm the charge cables and other components.

I'm running a straight connection on my 2006 RAM to 400 Ah of lithium batteries and quickly wore out the original 2006 vintage alternator, but that could be because the truck has 190k miles on it... haven't blown out the replacement alternator yet, but it has only been 6 months or so.

Edit - when I say a "straight connection" I mean I'm not using anything to limit current flow. There is a Blue Sea ACR in the circuit to combine/isolate the systems as appropriate.
 

ducktapeguy

Adventurer
I had somewhat of the same situation. Son has a 1998 Cherokee that we mounted a 100 Watt panel, run thru a smaller Victron controller/20AH Bioenno/Dometic compressor fridge. He is a Type 1 diabetic/swimmer and he keeps his food in there. Worked great in the California sun...not so well in the Ca winter.

Dreadlocks (and I hope he does not mind I am sharing this) offered up this suggestion:

If it were me, I'd pickup a Victron 15A, a small 12VDC dpdt relay, and a small 12v to 24v converter.. hook the converter up to a keyed vehicle source, wire the solar panel to the NC ports on relay, and the converter to the NO ports on relay.. then power that relay by a keyed ignition source.

When you turn the engine on, it will disconnect the solar panel and hookup the 24v converter.. the MPPT controller will be tuned to your charge params and convert it down to whatever voltage it needs.. then when you shut engine off, it'll hook the solar back up to the MPPT and let it finish/maintain it.


That worked like a champ! He is at school right now so no pictures, but here one of the panel on his jeep. The big advantage is the always temperamental Jeep electrical system is keep separate from the aux power.
That's so simple it's genius. Its exactly the type of answer I was looking for. I will probably do the same thing. I was wondering whether the charge controller would still work with the 13.8V input of the alternator, but with a converter I don't have to worry about it.

You use a DC-to-DC charger to protect the vehicle charging system and wiring, not the house battery. If you don't have something to restrict the amount of power the lithium battery is pulling it will run your alternator at 100% (or higher) rated output.

On an older vehicle it's not a huge deal - you might shorten the life of that 120A alternator, but for a modern vehicle with almost 400 Amps of alternator output you can seriously overwhelm the charge cables and other components.

I'm running a straight connection on my 2006 RAM to 400 Ah of lithium batteries and quickly wore out the original 2006 vintage alternator, but that could be because the truck has 190k miles on it... haven't blown out the replacement alternator yet, but it has only been 6 months or so.

Edit - when I say a "straight connection" I mean I'm not using anything to limit current flow. There is a Blue Sea ACR in the circuit to combine/isolate the systems as appropriate.
I want to limit current to 20A on the DC side because of the wiring, but I'm also concerned about getting the right charge profile for the battery and not over or under charging it. I'm not familiar enough with LiFe batteries to know whether that's a concern or not. My current setup never draws more than 13A in worst case, so I ran wiring rated for 30A.

You should read the ’specs of that battery. I think that Renogy is a ”drop-in” replacement for a lead acid. It should have built in BMS what makes it compatible to typical lead acid voltages and limits current when charging, whats probably .5C / 50 amps.
None the less 50A is fairly substantial load, especially if continuious for a few hours. Be sure your alternator is up to scratch for that added load.
I just bought it fairly recently so not too familiar with the specs yet. I do not want to over stress the alternator so ideally I'd like to keep the additional charging load to <20A.
 

john61ct

Adventurer
Renogy is not a great vendor, just relabel not a maker but a marketer.

Customer service can be OK, but I'd rather a top quality product.

BMS does not change the charge profile, chemistry is chemistry, LFP cells all require similar care specs, and the cell vendor data sheet usually shows maximum "do not approach" specs way too stressful for normal daily cycling if longevity is a priority.

C-rate for charging is ideally 0.4C or lower for longevity, but if fast charging is required, 1C won't be too stressful.

Very few stock alternators / VR combos can be run continuously over 40A, especially in hot weather conditions.

BMS does not limit current, cheap ones may not even hiccup OCP, at best latch cutoff then need resetting

often (worst case) just burn if limit exceeded.

So the DCDC is not just there to protect the charge source, very much there to let you set your charge parameters for getting good longevity from your battery as well.

Best to LVC before 3.1Vpc at rest, and

charge to (HVC) 3.45Vpc, no Absorb cycle required.

But the cheap BMS they use likely requires higher V being held for too long in order to finish balancing, maybe does not even give access to cell-level voltages.

Have yet to see a "drop in" unit I would recommend, very poor value even if the cells used are good quality - which is never disclosed either.
 

skyfree

Active member
I use a cheap Renogy 20A DC-DC charger and a cheap Renogy 10A solar controller separately for my rig. As others have said, the DC-DC charger is just there to meter the amperage coming from the alternator so the battery doesn't cause problems. It is turned on via a wire that is only hot when the truck is running, so 2 6awg wires connected directly to the truck battery (fused with 30Amp maxi fuse) and 1 thinner wire going to a circuit in the fuse box that is only on when the truck is running and connected via an "add a circuit" double fuse. That is fused at only 2amps. I believe this is the easiest way to do it.

I configured the DC-DC charger to charge at 14.0V.

I hardly ever use my portable solar panel but it's there if I need it. If you drive every day on your expeditions you probably won't need it. If you sit a lot you will.
 

ducktapeguy

Adventurer
I think I’ve had a change of heart and will probably go with a separate solar controller and DC-DC charger as suggested. Been doing a little more reading and it looks like using an MPPT controller as a dc charger might not be a great idea. I found a Renogy 30A combination dc charger and mppt controller, but for the price I might as well use separate controller and charger so I’d have a little redundancy in the charging.

i have heard renogy isn’t the greatest company, but I will say their marketing team does a great job of making things quick and easy to find. I was looking at Victron chargers and controllers and it just seemed like navigating their site and trying to find what I wanted was a lot more work for someone who didn’t already know what they wanted. Even trying to buy and price their stuff seemed cumbersome. I’m a spoiled Amazon customer, I want stuff that’s easy to find and buy, that’s probably why I have unintentionally ended up with a lot of Renogy products.
 

Rando

Explorer
I think I’ve had a change of heart and will probably go with a separate solar controller and DC-DC charger as suggested. Been doing a little more reading and it looks like using an MPPT controller as a dc charger might not be a great idea.
I have been doing just this with a DC-DC converter and my MPPT solar charger for several years. Works well with no issues and you only need to program one device - the MPPT charge controller.
 

ducktapeguy

Adventurer
Why is that?
I don’t remember where I read it, probably a solar forum or RV forum, but an MPPT controller could potentially short the input side of the controller. On a solar panel it wouldn’t be a big deal, but connected to battery or alternator that’s probably not a good idea. Not sure how true it is, but I assume there’s probably a reason it’s not used in this way very often.

Since the cost of a combination MPPT/DC charger is roughly the same as getting two separate devices, I didn’t see any advantage to combining them together and having a single point of failure. Same disadvantage with using a boost inverter and MPPT controller, if the controller fails I lose all charging capabilities. I’m guessing that’s probably why most people have It setup as separate circuits, at least most of the examples I’ve seen so far.
 

john61ct

Adventurer
I was looking at Victron chargers and controllers and it just seemed like navigating their site and trying to find what I wanted was a lot more work for someone who didn’t already know what they wanted.
Yes quality makers who want a worldwide network of serious dealers to handle customer support and aftermarket repairs

do not mass-market direct through channels like that.

If you want good value from quality gear like Victron, you'd be stupid to just buy based on price.

First find an authorized dealer with a great reputation for support

ask them for advice and guidance in designing your system and selecting the right models

pay their higher price that helps ensure the sustainability of their business

and use them as your first line of support if anything goes wrong.
 

jonyjoe101

Adventurer
No such thing as a lithium compatible charge controller, they all measure overall voltage and adjust output as required. I been using my ecoworthy 20a mppt (100 dollar) controller for years to charge my 220ah lifepo4 batterybank and also used it to charge my 312ah li-ion batterybank. The ecoworthy is a 10 year old controller and not lithium capable but it does the job, I just adjust the bulk/float settings to the battery.
I recently bought a 60a makeskyblue mppt (130 dollar) which states it is lithium capable but has no profile for lithium, you have to enter the bulk/float voltage for the battery you have manually(same as any non-lithium capable controller). This controller I had for the past year and it works great. This controller can be calibrated to the battery voltage (voltage drop) and it will also not produce voltage surges if the lithium battery bms is activated.
I encounter situations where the bms activated in both my lifepo4 and li-ion batterys while charging with solar, when this occurs on my ecoworthy and some pwm controllers I used, it produce voltage surges, these surges destroyed any 12 volt devices that where connected and running when the surges occured.
I reccommend the makeskyblue 60a because it wont produce voltage surges, its overkill for a 100 watt panel, but it will do the job and protect your 12 volt devices if the bms activates. Its the only controller that advertises that its controller will handle a bms that activates. The only drawback with the makeskyblue is the fan is loud when it comes on, but you get used to it after a while.
But ultimately the controller you have right now will work, just set the bulk voltage low enough so that it never activates the bms. I wouldnt recommend the victron or any other controller unless it can handle bms activation. I would read the manuals on any controller and see how it deals with a bms activation, that is the primary feature that is important when charging lithium. Also a feature to calibrate the controller to the actual battery voltage is a very good feature to have.

Heres a picture of the makeskyblue 60a mppt with my 365 watt panel, it was able to get 375 watts out of the panel.
1 365 performance.jpg
 

john61ct

Adventurer
Again, the canned profiles from all makers are not conducive to longevity.

User-custom profile adjustability is what makes a good LFP charge source

not marketing materials touting "Lithium compatible"

volts are volts, amps are amps
 
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