Charging Lithium Batteries With Alternator - Howto Guide

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In this video, I'm going to walk you through the process of charging your lithium iron phosphate (LiFePO4) batteries directly from your vehicle's alternator. This idea was sparked by a friend's van conversion project, aiming to efficiently power his house battery via the alternator. We'll dive into the essentials of using a DC to DC charger for this purpose, highlighting the critical differences between isolated and non-isolated chargers, and why it's pivotal for safely charging lithium batteries with your car alternator.
Understanding why a DC to DC charger is crucial forms the backbone of our discussion. Alternators are traditionally designed for lead-acid batteries, which have a vastly different charging profile compared to lithium batteries. The lower internal resistance of lithium batteries means they can draw higher current, potentially leading to issues if charged directly by the alternator. I'll explain how a DC to DC charger acts as a mediator, allowing your alternator to safely charge a lithium battery by regulating the current flow from your starter battery.
We'll explore several reputable brands like Renogy, Victron, and Litime, offering top-notch DC to DC chargers perfect for charging lithium batteries while driving. I'll share my experience with different models, including a cautionary tale about selecting the right type of charger-emphasizing the importance of choosing a charger specifically designed for your setup.
The video includes a detailed wiring diagram for connecting your DC to DC charger, using a Renogy model as an example. Tips on minimizing voltage drop, selecting the proper fuse sizes, and the advantages of wiring your charger through a switch for greater control and efficiency will also be covered. This setup is particularly useful for those who might alternate between alternator charging and shore power, aiming to conserve fuel and reduce wear on your vehicle's alternator and belts.
Additionally, I'll tackle the often-asked question about the differences between isolated and non-isolated DC to DC chargers. The choice between them can impact efficiency, cost, and the safety of sensitive electronics in your system.
To debunk myths and clarify misconceptions, I'll discuss a Victron test that highlights potential issues with charging lithium batteries directly from an alternator without proper current regulation. Plus, I'll share insights on how to properly size your DC to DC charger in relation to your alternator's output to ensure longevity and reliability of your charging system.
If you're curious about how long it takes to charge your battery with an alternator and a DC to DC charger, I've got you covered. We'll break down the math to give you a clear understanding of charging times, ensuring you can plan your travels without worry.
This video is packed with information for anyone looking to charge their lithium battery from a starter battery, especially for those on the move. Whether you're driving to your next adventure or powering your off-grid setup, understanding how to efficiently charge your lithium batteries with your vehicle's alternator is key.
Your feedback and questions are invaluable, so please share your thoughts in the comments below. Have you used a DC to DC charger in your setup? Share your experiences and let's help each other out.

[@tomede472]

Thanks always very interesting and professional explanation about electronics.

[@canyondan]

Excellent information

[@gregsnape9622]

Really good information, thank you.

[@zenzen9131]

Perfectly explained :)

[@sranjaniis]

Good info . Short and to the point videos . No complains .

[@cleversolarpower]

Glad you liked it!

[@deborahdoyle6743]

Excellent video. Thank you.

[@markoshun]

Excellent videos. Some of the best on any subject, especially considering how complicated this is. Clear, concise. Thank you.

[@cleversolarpower]

Glad it was helpful!

[@dan32one44]

Good stuff 👍

[@cleversolarpower]

Thanks Dan!

[@VanVentures-oo7bm]

I'm doing research for my ambulance tiny home build and im pretty sure you solved a major problem of mine with this video. Here is my plan. My abulance has 2 alternators i beleave 120 amps each that normally charge 4 agm batteries as a 12volt system. 2 for starting and 2 for box accessories. I want to replace the 2 agm batteries for roughly 300AH 24v. I want a 24v for Air conditioning efficiency and limit amperage of the system in general. My problem was the alternator possibly overheating because of that shotty victron alternator video. I agree with your assessment about it. So i think the 12-24v sterling power dc to dc is perfect for what im doing! Thanks so much.

[@cleversolarpower]

I've heard the sterling power dc to dc charger is great (but expensive).

[@LintiNuci]

Salu Mulțumesc pentru explicație. Poti pune mai multe sutitrari sa inteleg mai bine! mulțumesc

[@michaelburke1023]

Redarc brand is another certainly worth mentioning

[@Tom-Travels]

Mein Gott! Das ist wonderbar!

[@cleversolarpower]

Glad you liked the video Tom!

[@garyjunker83]

Very professional and good information. Thoughts on a Precision Circuits LI battery isolation manager vs B2B??

[@brucew4726]

I'm charging my 105amp Lithium phosphate battery with a Sterling BB1260 on the 30amp reduced power setting. My Peugeot Boxer van will charge the battery at around 25 amps until the battery reaches around 75% charged and then the charge voltage drops to about 10 amps and then 8 amps. I'm using 110 amp cable from the starter battery.

[@seancarwin8034]

Hey good day I would like for you to do a video and how to wire a shunt to a 12 volt battery

[@stanleybest8833]

Zeftronics regulators control voltage and amperage. Charge any battery of the correct voltage.

[@halfaistos]

Very informative video! In my opinion, one of the best on KZbin on this subject.. definitively because of the drawing illustration! I just currently debate on BBC Forum "how to protect the alternator", actually, by presenting the video you mention; "How not to blow up your alternator when charging Lithium". You've mention on the video that they make the experiment to fail and you present facts to prove it. However this scenario on their video... precisely exist on my boat; Mercury 150hp has only 60Amp alternator in tight space, hot under the cowling and is forced to charge dual purpose 120Amp 1100 CCA battery. I'm going to use Victron DC/DC isolated charger 18Amp (the only info given to me by some reputable Utuber) Would you installed in this situation higher amperage charger like 30,40amp? What size of circuit breaker or fuse would you use? Could you - by using your magic pen -draw lines from alternator-fuse- dc/dc charger-battery please? Thank you!

[@cleversolarpower]

Thanks! In that case you should use a DC to DC charger. It depends on how quickly you want to charge your secondary battery. If it doesn't need to be charged quickly, then no need for a higher current. Please take a look at my video about selecting fuses and wires. For a 18A version, multiply by 1.25 to become a minimum fuse size of 22.5A. This doesn't exist, so choose one up, which is 30A midi fuse. Then select a wire that can handle at least 30A. This is an 8gauge welding cable.

[@TheJR914]

All those comments make sense. I am using lithium batteries for my truck (diesel) and cars as the only dc source. All of my batteries are DIY built using smart BMS’S on all of them. I can program the amount of charging current both input and output on the BMS’S and I have never had a problem with the alternators. All alternator has a regulated output the voltage can only go but so high no matter what rpm it is turning 750 to 7000 rpm. I also run lithium on my motorcycles with the same concept no problems for many years.

[@cleversolarpower]

Thanks for sharing your system. How do you size the current limit of the BMS? 50% of the alternators rated current?

[@TheJR914]

My BMS’S DEFAULT IS 110AMPS . This can be change to anything lower its label over current in the settings BMS. Any alternator that’s has a built in regulator will limit the current draw to a load when it reaches its saturation point. Any load is determined by its resistance or inductive load. The BMS uses this same concept in limiting the current to itself.

[@kais7137]

Very interesting video, thank you! It makes me wonder if there is a solution for my problem; I'd appreciate any ideas. I have 2 Honda outboards, each with a 12A charging coil. I also have a 40Ah and a 100Ah LiFePo battery. Is there a way to use the batteries for starting the engines and to charge the batteries from the engines? I guess with the DC to DC charger, I could safely charge the batteries without damaging the coils (what would be the right charger here? 12A? does that exist at all?). But then, the current cannot go back to the engines when I want to start them, right? Or is there a solution? Many thanks in advance!

[@zaneenaz4962]

Charging with lower Currents extends your battery life. Under 0.2C has been often recommended. C =rated current of battery. Typical 100A alternators can deliver most of their power to the low internal resistance lithium batteries

[@bobk3745]

I'm charging a 100 AH lifepo4 battery from either solar or the onboard (RV) converter. My battery charge line (pin #7 on the 7 pin connector) from my dual alternator GMC diesel truck is protected by a 30 amp fuse. Can you tell me how the alternators could be damaged by an over amp condition when the charged line is fused? Shouldn't that fuse blow before alternator damage? Thanks

[@42kwhaum2]

i have 90Amp alternator (Sailing boat) and 280AH Lifepo4. I charge directly from the internal regulator. No problem. I use 20mm2 wire, it 's hot but it's limit DC current in this configuration. I dont use BMS for protect diodes in regulator (running with battery swich off)

[@cleversolarpower]

Did you measure the current going through it?

[@GaryRust-xj7yt]

I have 20A Renogy DC to DC charger. The installation is as per Renogy to my 12 volt 100A lithium battery. The system starts to operate and within 3-5 the cooling fan starts and within another 3 minutes the fuse trips. Any idea where I have a problem?

[@eroenker]

I've seen a few videos of overlanders using an Orion 12/24 DC-DC converter to fast charge their power banks via MPPT input. Seems like a pretty good solution for 48v systems. Is that a good option?

[@cleversolarpower]

The input of the charge controller needs to be above the battery voltage. With a regular dc to dc converter, you risk draining the starter battery.

[@TheBioniXman]

Not sure that I understand this as on many motorcycles there aftermarket Lithium batteries available to replace the standard battery using the same charging system. I ran one of these on my Ducati for 2 years with no problem. BMW and Ducati both offer a Lithium battery option with the standard motorcycle alternator charging system.

[@cleversolarpower]

That's weird. Maybe they have a smart alternator that limits the charge current?

[@andrewwhite986]

They have current draw resistors on the circuit board inside. Design to stop over charging and limit the current. Though these are usually very undersized.

[@robinhooper7702]

Hi, I love the way you teach. I'm learning a lot from this just one vid, thus far. Thank You. My application is to charge my Lithium Ion batteries(6), wired in series, 12V at 10amps(?) each, which is how my E-bike was assembled, by the supplier. I have retrofitted an alternator that its' rated output is at 12V-145amps. The original setup had my E-bike last only 1-1/2 summer seasons. Very poor for a 3K purchase. At 8:10 you mentioned that I would need a Lead Acid battery to do what I'm planning, Yes? As well as a DC to DC converter. I have, as a gift got a LiFePo4 battery(1). Can I use this Battery instead of a Lead acid one? Since my existing Lithium battery bank is toast, I would much rather use LiFePo4s. Will I still need a Lead acid battery connected straight from the alternator? As far as an isolated and non-isolated converter is concerned. How would I be able to tell if I have sensitive electronics in my e-bike? Since I will be replacing my Lithiums' Do You have a recommendation for a LiFePo4 supplier? Thanks again for sharing your knowledge in these vids.

[@cleversolarpower]

I'm afraid I don't understand your question. Have you fitted an alternator on an e-bike? If you have a small lifepo4 battery (100Ah or less), you might get away with connecting it to the alternator directly, since you have a 145A one. Add some voltage drop in the wires and test the current coming out of the alternator. Max should be 75A.

[@robinhooper7702]

@@cleversolarpower Hi, thanks for your reply. And, yes I fitted an alternator to my e-bike. I'm a cabinet maker so I'm not that versed with electronics. How would I add a voltage drop?

[@TheoSmith249]

@@robinhooper7702Install a resistor use ohms law to to determine value. Resistance is = to Voltage divided by current R=E/I

[@robinhooper7702]

@@TheoSmith249 Just so that you and I are on the same page. I have a source of 12-13.5 Volts at 145 amps. And I need 5 amps at 72 Volts to operate my ebike. So I would need a Buck Boost Converter to do that. Yes?

[@garymiller7870]

Nice overview, i can see how the DC-DC charger isolates and protects the LFP house batteries but how does this protect the alternator? I have a 120A alternator with a Balmar MC-614 regulator and an Orion XS 12/12-50A charger. At 2800 alt rpm, fast idle, the alternator puts out 65-70A, hot, but at idle,1600 rpm, the alt puts out 30 to 40A. As the charger draws 50A the alt quickly overheats at idle, triggering the temperature field limit. Where does the 10 to 20A come from, the starting battery? As the alt cools down the amperage ramps back up and the temp maxes out again. So if sitting in traffic the starting battery and alternator are suffering high temperatures and oscillating voltage etc. How is this prevented? It would seem the field voltage should be limited and or the alternator substantially oversized? How is the field voltage limit determined? Does this system really need a 200A alternator to supply a consistent 50A to the house batteries?

[@Energy_69]

Alternator is pretty much the generator, lower capacity alternator overworking with heavy load it’s obvious will get damaged in the long run ! If you want to run a lot of batteries, you need bigger alternator but you still need to consult with a specialist ti find out if this change will effect electrics into your vehicle from this high current

[@TheCornucopiaProject-bd5jk]

You don’t need a switch for the renogy dcdc50. It senses the higher charging voltage on the starter battery to turn on and off. And with solar connected, alertât or charging is limited to 50% or 25 amps, solar would bring in up to an additional 25 amps.

[@cleversolarpower]

A switch is recommended if you are approaching a campground. Turning on the DC to DC charger while driving will consume more fuel. So turning it off is better at that moment.

[@rickss69]

The problem is not the charging...it's the BMS. If it shuts down for any reason there will be a spike which will kill most electronics. If you had a lead/acid battery hooked to the lithium battery you would be safe, but who wants to run dual batteries just to have a lithium.

[@cleversolarpower]

Never had a voltage spike from a BMS that turns off.

[@GaryRust-xj7yt]

I have a Renogy 20A DC to DC battery charger that has been installed as per Renogy's info. When the charger is in operation for about 2-3 minutes the cooling fan starts and within another 3 minutes of operation the fuse trips. The green led is on during this period. Can you suggest where my problem might be.

[@cleversolarpower]

Fuse size: 20A*1.25=25A minimum. Which fuse do you have installed? Send me an email because i don't get notified of replies here.

[@tomywrobel6428]

What would u recomment i am building i am building 500ah battery lithium ion need to put in to semi truck for apu unit to run longer what will be best way to do that

[@user-ot5ck3oh8b]

Lithium ion is completely different than (LiFePO4) batteries and don't use one instead of the other.

[@claeslind9532]

I just bought the ecoflow alternator charger, still haven’t arrived though

[@cleversolarpower]

Seems to be a new product. I will await some reviews from people online.

[@cleversolarpower]

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[@freespirit5944]

So why not use an inverter like the renogy 1000w dc to ac from alternator to charge the battery or power instead? That would increase the wattage therfore charge quicker especially when solar is unreliable

[@cleversolarpower]

Car alternators produce 12VDC, not AC.

[@freespirit5944]

@@cleversolarpower yes, that's exactly why you would connect a dc to ac inverter to your car battery. Then you can plug your battery bank into it and charge as if you were charging it from the wall. There would be a slight energy loss due to the conversion but you'd still be able to get 750 - 800 watts from the inverter which is more than most dc to dc chargers provide.

[@ptcclatlptcclatl1683]

Why not wire the DC to DC directly to the alternator?

[@cleversolarpower]

It's hard to reach and the battery already has terminals on it.

[@creativegoot]

Why to use DC-DC charger at 50% of the rated current of the alternator ?

[@librulcunspirisy]

So you don't blow up your alternator

[@grvsays]

How to diy DC dc charger

[@cleversolarpower]

I don't have experience with that.

[@stuartstuart866]

I purchased a bluetooth monitored 100Ah LiFePO battery . It would be a great addition if battery manufacturers allowed owners to set their own charge rate from an app. This way no other expenses like heavier wires or DC to DC devices would be required at slow charge rates. Hmm, maybe even an interior charge converter so you could charge directly from solar panels as well. There is so much empty space in battery cases, maybe this could be done?

[@cleversolarpower]

I never heard of regulating the current input of a battery with the BMS. What brand does this?

[@fratermus5502]

@@cleversolarpowerSome high-end batts will talk to an external regulator over CANBUS to control alternator output. I don't know of any retail BMS that limit charging current to a given level.

[@Energy_69]

My car alternator is 140V ,..I would like to attach a 12v 100Ah lithium battery ,…but I do find it unnecessary to install DC to DC charger ! Battery charging voltage is 14.6V ,…while my car alternator doesn’t reach that high only 14V I have seen some videos when the car is switched on but not driving , only produces around 250 watt to 300watt ,..when hard accelerating it climbs to around 400 watt or 450 watt only some time might reach split second spike to around 500 watt ,..but as I said must be some crazy accelerating , it’s impossible to keep that kind of rhythm would damage the engine ! So based on facts, and my style of driving,..I don’t think I would exceed 350-400 watt maybe even less while driving , facts going against the DC -DC charger ! I would like your advice based on this information, do I need DC to DC or not ?

[@cleversolarpower]

I assume you meant 14.0V. If your lithium battery is depleted, the alternator will still deliver a lot of current. The reason you are seeing 300W is because the lead acid starter battery is charged. You can try it and let us know the results 😉

[@Energy_69]

@@cleversolarpower Thank you for your reply I want to buy a 12v 100ah lithium battery to power my 12v fridge freezer during the summer while travelling with my car,..but the problem remains charging the battery, I do not want power station or portable solar they are too expensive and not very useful to me , I just need some power for the fridge when the engine is off ,…I’m thinking to use the alternator when the engine is running to charge the 12 volt 100ah lithium battery,..but don’t know what is the best idea ! Some people say use relay , some like you say dc to dc ,.not sure what is the cheapest and efficient way to charge 12vl 100ah lithium battery and to keep the fridge running ,..I hope you have some kind of advice thank you

[@philbrooke-little7082]

These are not needed, all you do is effectively add the lead acid resistance to the lithium charge path and the simplest way to do this is to simply extend the charging lead. Because the charge curve of the lithium is so flat the current and voltage drop remain almost constant. 100s of boaters have done this and saved a lot of money. DC-DC chargers are expensive, inefficient and often limit the current more than needed. You are actually using the voltage drop of the cables to your advantage. You only increase the length, you always keep the CSA large enough to carry the maximum rated current of the alternator. It is also perfectly possible to fry an alternator with a DC-DC converter. I use the long wire method on my boat and have been for some years and it works fine. My truck sadly has a 24v engine system and 12v domestic and so this uses and Orion horribleness. 70A 24v alternator, 30A Orion meaning it takes only around 20A (wasting 120W) from the alternator which is capable of a lot more. Needless to say the ‘lithium profile’ default of the thing was designed to damage the batteries through overcharging over time with a 2hr absorb at 14.2v going completely against cell manufacturer’s recommendations but it will of course mean they sell more batteries by reducing their lifespan.

[@cleversolarpower]

Did you watch until the end? I talked about this, but it's risky if you don't know what you are doing. If you do not look at the voltage of the starter battery and leave it on while the alternator is not running, you can drain the starter battery. You can set the charging parameters of the orion to a lower voltage, so your battery doesn't get 'overcharged'. Its possible, but i do not advice it ;)

[@philbrooke-little7082]

@@cleversolarpower I did watch to the end. You use a conventional dumb split charging relay from the starter battery operated by the D+ (warning light) terminal. I have suitably modified the Orion settings to avoid it overcharging the Renogy dumb battery. I will be fitting a JBD BMS, which I have lying around, to the Renogy batteries to give them management capabilities, rather than last ditch protection, and just leave the one in the battery to deal with balancing and cell over / under voltage. The JBD can then act as an overall charge protection from the various charge sources, some of which can’t be modified.

[@mikez9929]

😂 'promo sm'

[@hufman9807]

Should be called, "charging lithium battery with lead acid"...

[@reveal-lk6ip]

The author! Have you eaten too many mushrooms? During engine start, the starter consumes more than 250-300 amperes!! Your DC-DC converter connected in parallel to the battery will die in seconds!

[@cleversolarpower]

I don't think you know circuitry. When the engine starts doesn't mean it gets sent to your DC to DC controller. If you put on a kettle, your lights are not going to shine brighter.

[@marcbloch1963]

The company „Battleborn“ is advertising on their website a battery isolation manager (BIM - made by Precision Circuits) specifically for lithium batteries which monitors voltage and connects batteries when needed. Under normal charging conditions, the BIM will connect for 15 minutes every 35 minutes. That means that the BIM will connect for 15 minutes, disconnect for 20 minutes, and repeat this cycle until the coach battery is charged. I was wondering if I could install this device in my van instead of a DC to DC charger. Your thoughts please.