Exploiting a large alternator via battery-to-battery chargers?

[MTVR]

Our truck came with a 150a 24VDC alternator. In addition to solar, generator, and shore power, I'd also like to be able to use the alternator to charge our house battery bank as we drive from one place to the next.

If I understand correctly, I can charge lithium batteries much faster than lead-acid types, at the rate of around 40% of their capacity. So if we go with a lithium house bank, that would give us a unique opportunity, as we'd have a lot of power available to charge the house bank, and a house bank capable of taking a lot of power quickly.

I've been looking at Sterling's web site, and the largest 24VDC to 12VDC charger I see, is 35 amps in and 70 amps out. If we had a 400Ah lithium house bank, 40% of that would be 160 amps, or almost twice what that charger is capable of.

Are there larger 24VDC to 12VDC chargers available?

Can I parallel multiple 24VDC to 12VDC chargers for more amperage?

 

[DiploStrat]

24v to 12v is tricky. I suspect that you can parallel Sterling Power units - ask 'em. I know that you can parallel REDARC units - I did ask 'em.

When it comes to charging, the advantage of lithium is that the internal voltage tends to remain constant and thus the battery will take its charge at a constant rate. (Unlike lead acid where the charge rate drops as the battery internal voltage rises.)

While more is always more, you may find that 30-50A is actually enough as a lithium bank will tend to continue take that full amount until fully charged. With a lead acid bank you will watch that charge drop steadily as the battery bank charges. I might be inclined to start with one B2B and then see if you really need more.

YMMV, free advice, etc.

 

[1000arms]

Our truck came with a 150a 24VDC alternator. In addition to solar, generator, and shore power, I'd also like to be able to use the alternator to charge our house battery bank as we drive from one place to the next.

If I understand correctly, I can charge lithium batteries much faster than lead-acid types, at the rate of around 40% of their capacity. So if we go with a lithium house bank, that would give us a unique opportunity, as we'd have a lot of power available to charge the house bank, and a house bank capable of taking a lot of power quickly.

I've been looking at Sterling's web site, and the largest 24VDC to 12VDC charger I see, is 35 amps in and 70 amps out. If we had a 400Ah lithium house bank, 40% of that would be 160 amps, or a little over twice what that charger is capable of.

Are there larger 24VDC to 12VDC chargers available?

Can I parallel multiple 24VDC to 12VDC chargers for more amperage?

If you run a 24V battery bank of FLA, AGM, or 24V LiFePO4 (DON'T put LiFePO4 batteries in series for 24V), then look at Sterling Power's 24 Volt 200 Amp Alternator-to-Battery Charger:

Sterling Power DC Input Battery to Battery Charger 24 volt, 200 amp dc alternator powered battery charger

Charge your batteries up to 5 times faster and extend their life at the same time with a Sterling Power USA 24 volt 200 amp alternator to battery charger

www.sterling-power-usa.com

If you need to use a 12V battery bank, there is the Sterling Power DC Battery to Battery Charger 24V input to 12V output at 70 amps:

Sterling Power battery to battery charging system - DC to DC smart battery charger, marine grade DC powered charger 24v to 12v

DC to DC converter. Charge your auxiliary battery bank with the correct multistage, temperature compensated charging curve by using the input power of any vehicles alternator thru the start battery system automatically while the vehicle is running.

www.sterling-power-usa.com

 

[DiploStrat]

Edited to add: 70A @ 12v is a LOT of power. Typical all electric campers - that is induction stove, microwave, refrigerator, etc. can expect to use between 75Ah to 125Ah depending on weather. Hot weather increases demand from the refrigerator, cold weather pulls power to run your heater motor. As always, your exact numbers will vary.

I have an older REDARC and get 40A max into AGM batteries. 70A would be close to the practical maximum into AGM because of internal resistance. 70A with lithium would get me a full recharge in around two hours, not counting anything from solar. Nice.

 

[1000arms]

Edited to add: 70A @ 12v is a LOT of power. ...

It is, but what does that make drawing up to 350 amps, for a short time, from a 36V battery bank? ...

Ready Welder

readywelder.com

Hey @MTVR, you might want a Ready Welder to help repair other people's frames, if you drive your MTVR down the parking lanes!

Or for making sculptures out of mopeds?

 

[john61ct]

If I understand correctly, I can charge lithium batteries much faster than lead-acid types, at the rate of around 40% of their capacity.

No, many times higher, much faster than is healthy for them and can burn out your alternator too.

The two functions of the DCDC are A to ensure correct voltage input to the bank, and B to reduce the current draw to a reasonable level, protecting both the alt and your cells.

Sterling makes good units, including 24 to 12V.

But why not configure your LFP bank as 24V? use step down DCDC for loads that need 12V.

Just stack them in parallel if you need to get higher amps. But lower is healthier for the cells anyway if your trips are long enough.

 

[DiploStrat]

...
But why not configure your LFP bank as 24V? use step down DCDC for loads that need 12V.

Just stack them in parallel if you need to get higher amps. But lower is healthier for the cells anyway if your trips are long enough.

Would agree with this. My truck was wired backwards, that is, a 24v to 13.5v "equalizer" on the charging side. With lead acid, this would assure perpetually undercharged batteries. But with a 24v camper bank, a 13.5v equalizer would provide perfect voltage for your "12v" loads. I didn't have the option as a 12v inverter/charger had already been installed.

N.B. You may still want an B2B to protect your alternator.

 

[john61ct]

The system should be designed as a system.

Compromising to accommodate existing gear leading to a suboptimal overall design

penny wise pound foolish.

Maybe "make do" temporarily, but each replacement / upgrade should lead toward the optimal design.

 

[MTVR]

No, many times higher, much faster than is healthy for them and can burn out your alternator too.

That's why I'm planning to use a DC-DC charger between the truck's alternator and the house bank.

The two functions of the DCDC are A to ensure correct voltage input to the bank, and B to reduce the current draw to a reasonable level, protecting both the alt and your cells.

Sterling makes good units, including 24 to 12V.

Just stack them in parallel if you need to get higher amps. But lower is healthier for the cells anyway if your trips are long enough.

Yeah, I got all that.

But why not configure your LFP bank as 24V? use step down DCDC for loads that need 12V.

How do I step down 24V for 12V winches? Have a separate "winch battery" and a dedicated 12V charger for it?

 

[DiploStrat]

...
How do I step down 24V for 12V winches? Have a separate "winch battery" and a dedicated 12V charger for it?

Eaton (and probably others) sell "equalizers: that will act as a step down transformer. 100A may or may not be adequate for your needs

21100 Family of Battery Equalizers

 

[MTVR]

Eaton (and probably others) sell "equalizers: that will act as a step down transformer. 100A may or may not be adequate for your needs

21100 Family of Battery Equalizers

100 amps would probably do it, but yikes...that's $700, just to allow me to run a 24V house bank.

 

[MTVR]

The system should be designed as a system.

Compromising to accommodate existing gear leading to a suboptimal overall design

penny wise pound foolish.

Maybe "make do" temporarily, but each replacement / upgrade should lead toward the optimal design.

A pair of small ATV winches take up much less space than a pair of linear acuators long enough to perform this function, and I would still need the third winch to pull the motorcycles up the ramp anyway...

 

[DiploStrat]

Do the maths both ways. If you need a B2B to protect your alternator from the demands of a large lithium bank any way, then it may be more effective to use a B2B that can reduce voltage at the same time. Check also the cost of a 24v vs, 12v inverter/charger.

In my case, the 40A REDARC has worked perfectly for a couple of years. With a 24v bank I could have used a smart relay, but that might have led to a failure if/when I move to lithium. I have done tests with a fully discharged 100Ah lithium battery and nearly melted some jumper cables. A B2B will not pass as many amps, but it can have advantages:

-- With lead acid, it will get the voltage up to where you want it, assuming that your truck's system does not do this.
-- With lithium, the reduced amp draw will protect your alternator.

And, of course, if you keep the truck at 24v and the camper at 12, then a B2B can perform the voltage reduction.

N.B. If you are considering large winches, a 12v winch may be easier to find/afford, but they can pull well over 100A.

There are many ways to do this; each with trade offs in cost and features.

Our boy John likes to be snarky and patronizing, but he is not wrong - you want to design the whole mess as one integrated system. In my case, I was buying a used vehicle and it cost me a lot of money, including discarding an Eaton equalizer, to get something that works.

Best wishes!

 

[john61ct]

How do I step down 24V for 12V winches? Have a separate "winch battery" and a dedicated 12V charger for it?

No, find out the power drawn and look at DCDC buck converters.

High amp units do get pricey.

Having dual banks on separate circuits is another way, probably cheaper but more complex.

If you know 12V is best, cheapest option might be replacing the alternator.

Ex emergency vehicle large-frame units designed to output rated power for long periods can be found very cheaply on eBay, also local junkyards, auto electric rebuilders. . .

 

[john61ct]

Our boy John likes to be snarky and patronizing

Ex squeeze me?

Trying to interpret "tone" in text posts is pretty futile

I try to be helpful and just state the facts as I see them.