Charging 24v from 12v chassis (1 Viewer)

[LandLocked93]

Just marking the territory in case anyone else discovers how not straight forward finding an answer actually is. I've searched this forum and found not much in regard to going from 12v to 24v.
The question (in question) is how does one charge a 24v batt bank from a 12v system.
The answer is RedArc's BCDC2420 charger.
E-trailer.com, RedArc's US distro, does not carry them. But I have a call in and they should have them on their website in a week or two. Their initial answer to the question was, "You need two BCDC12xx chargers, one for each battery, then arrange a disconnect method between the two batteries." Wholly or in part, this is not acceptable.
It is surprising how little there is out there in the way of addressing this seemingly simple need to charge a 24v bank of 2-12v batts in series from a 12v alternator/aux batt source.
No one else, best I can tell, has a device that does just this very thing - and also integrates a solar MPPT controller.

Admittedly, my realization of this could seem completely elementary to the 24v folks here. And for that I apologize. It's just that going out and searching for such a solution sent me down weeks of rabbit holes and half-solutions when I thought it would be pretty straight forward to find what I needed.

Cheers and happy trails!

 

[BreckenridgeCruiser]

Can I ask why you need a 24v bank when your primary voltage is 12v? Most of us have issues (and desire) going back the other way!

 

[LandLocked93]

Can I ask why you need a 24v bank when your primary voltage is 12v? Most of us have issues (and desire) going back the other way!

While there is give and take between the two, the more efficient use of current by and large is what I find attractive.
But indeed, my searches revealed the headaches of those with 24v chassis wanting to go to 12v. I think I'd be pulling my hair out too.

 

[BreckenridgeCruiser]

If you need 24v regularly in that rig/setup, you could add a second alternator (24) to charge the bank... Would not be portable, but would be more efficient than using a charger, and you can use the 24v system while "charging". Only caveat is that you'd need to avoid common ground and wire all grounds back to the low side battery...

 

[LandLocked93]

Wellll...it boiled down to cost. A charger (in my case off ebay for a song) was much less expensive than adding an alternator. Tho I would prefer the alternator (I think). Are you saying there's a 'kit for that'?
And thanks for the common ground separate tip. Incidentally the charger doesn't require separation, but great to know if I do the alternator at some point.
However, the 'low-side battery'...does that come into play in my situation using chassis ground for both 12/24? My research suggests no, and the charger manufacturer requires they be common, but I'm open to all arguments otherwise.

Main goal is to not burn my s*** down.

edit: I'll still be using solar for additional charging, so there would still be a charger in the system even with the additional alternator. Plus the inverter handles shore power duties to the bank so it's an option too (while it lasts, lol - apartment-dweller joke).

 

[BreckenridgeCruiser]

In 24v land we always call the ground - to 12v + battery the low side, and the 12v - to 24v + battery the high side... Mounting would depend on the engine and vehicle to see what kind of brackets you'd need.

I agree about not burning s*** down. That was why I thought the alt would be simpler, be isolated (so if anything goes wrong, you don't fry your get-home electrical system), and would be more available to handle larger loads or shorter charging cycles.

Two things to consider... Charging two 12v batteries that have been drained off of a standard or even moderately upgraded alternator with chargers as you describe will not be quick. This is especially on charging to 'full' which takes a lot longer than the middle of the charging cycle. Think of it like a mile run at high speed... You may run the same speed, but the last half lap takes the most effort. Same with charging a battery... It takes longer and more energy to get the last half to full volt into that battery. Do that with two and it takes even longer, especially with whatever draws you have on your system while running.

Having a dedicated alt means that the alt is charging one 'battery' (two 12s equals one 24v battery in the eyes of a voltage regulator) and it is one alt to one battery as opposed to one alt to three (the two for the 24v house system and the third chassis battery).

Hope all that helps!

 

[LandLocked93]

In 24v land we always call the ground - to 12v + battery the low side, and the 12v - to 24v + battery the high side...

OK, so to make sure i know what's going on, I would call your 'low side' the series connection between the two batts and your 'high side' the 24v output +&-. Are we saying the same thing or no?

Mounting would depend on the engine and vehicle to see what kind of brackets you'd need.

It's US 80 series, '93, 1FZ. If it mounts starboard that's a great start. Made room for a York OBA, but decided to stick with electric air. The R12 AC doesn't work and I have no plans to r&r, so that can go too if necessary.

.. handle larger loads or shorter charging cycles.
Two things to consider... Charging two 12v batteries that have been drained off of a standard or even moderately upgraded alternator with chargers as you describe will not be quick.

Indeed short charging would be great. It would take 40hrs or more for this charger to fully charge the bank from 9v or something like that. I'm expecting it to be more of a tender via solar when parked or alternator when running. And the 24v system is shutoff (no load) when the truck is moving (unless trailing at night which is rare), so no loads when not camped out.
But it's gotta cut the mustard or an alternator may be in the cards.

Thanks for the help indeed.

 

[BreckenridgeCruiser]

Close...

Low and high describe the batteries and not the connections... Essentially the first battery in the series (low side battery) get the system to 12v. The second battery in series (high side battery) adds its 12v to the low side battery's 12v so that its positive side brings the system to 24v.

This will help when researching here on mud as many of us use these terms when describing wiring setups and other diagnosing of issues.

Sounds like if you only use the 24v system when camping, and don't need it while driving, an optional setup may be to wire you system as a three battery 12v system for charging/driving and then use a switching system to isolate and series the second and third as 24v when camping.

Another whole idea is to keep everything as 12v and just have two house batteries to run your camping setup... Essentially while not 24v, you will have essentially the same capacity due to running the two batteries as a larger 12v bank instead of a standard 24v... Ohm's law says that the efficiency will be similar either way with the correct wiring.

Last thing is that I went through a similar deciding process and since I have more than one truck I may take camping (and an old m416 trailer for larger trips), I have been leaning towards a portable battery solution I can move from rig to rig without a permanent install. This way I only need to buy one system for all situations, and I don't have to always have my truck there to have power in the trailer to run a fridge or something.

Hope all this helps!

 

[LandLocked93]

Close...

Low and high describe the batteries and not the connections... Essentially the first battery in the series (low side battery) get the system to 12v. The second battery in series (high side battery) adds its 12v to the low side battery's 12v so that its positive side brings the system to 24v.

This will help when researching here on mud as many of us use these terms when describing wiring setups and other diagnosing of issues.

Ok, I think I got it.
The low-side battery is the battery providing the negative 24v terminal, and the high-side battery is the battery providing the positive 24v terminal?
The "low-side positive" is the positive terminal on the "negative 24v terminal" battery?

Ohm's law says that the efficiency will be similar either way with the correct wiring.

Yeah but lower circuit current means less fire hazard, at least. And it allows for some serious inverter wattage when needed on not so astronomically-priced cabling and circuit devices.

Last thing is that I went through a similar deciding process and since I have more than one truck I may take camping (and an old m416 trailer for larger trips), I have been leaning towards a portable battery solution I can move from rig to rig without a permanent install. This way I only need to buy one system for all situations, and I don't have to always have my truck there to have power in the trailer to run a fridge or something.

Agree 100%. I'm not really sold on the 'power stations' you can buy right now.
Needs more cowbell.

Thanks for the help.

 

[BreckenridgeCruiser]

Yep! You got lots side and high side now.

I definitely understand the benefit of 24v. I love it in my rig and since it uses all the same wire as a 12v 40 series, then it is a bit safer...

With that in mind, since your are wiring the system yourself, you could always use a larger guage wire to lessen the resistance and therefore the fire danger... May be less expensive in the long run!

Just throwing out options!