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12V to charge 24V system

12V to charge 24V system

(OP)
Hey guys, I'm new here so please bare with me.

I have a vendor trying to supply us with a vehicle using a dual battery system and charging at 24v. The entire vehicle including starting, operation and auxiliary is 12v.
First of all, I would like to tell problem that I faced on my project. We were install 24V Lithium Battery(Victron Battery) in our car (12V,90A Alternator) and this battery directly connected to the starter battery (Victron AGM Battery).The starter battery were connected to 12-24V converter to charge this 24V Lithium battery. The connection is simple, from the car alternator -> starter battery -> 12V-24V converter -> 24V Lithium Battery.

However, what we facing today is the car battery burn and puffed-up. Maybe car battery cannot support to charge 24V battery even we use 12V-24V converter due to 12V battery is half power compare to 24V battery or different type of battery using for this system (starter battery used AGM battery to charge Lithium battery) I also not really sure.

Can I have your advice to settle down this problem


Any information will be appreciated.

RE: 12V to charge 24V system

A schematic might help to be sure. Taking care to develop it as built may show a wiring error, and thus your cause of distress. I'm assuming the low side of everything is grounded to the chassis. Is the 12-24 DC-DC converter an isolation device? Will it prevent backflow? If your DC-DC converter failed, was misconfigured, wired wrong, etc. could the 12V battery be in the ground path of the 24V battery?

Is your 12V battery grounded to the chassis, or is it installed in series with the DC-DC converter?
You might check voltages across the 12V battery, DC-DC, 24V, etc during operation to see what is really happening during operation and charging.

I would take a lot of care with this, the next time you could lose more than a battery. Risks include battery explosion, chemical burns, fire, hazmat fire (prolly already had that), cooking your wire harness and car electrics(12V system sees 24V).

RE: 12V to charge 24V system

In general, a DC-DC converter is not the same as a battery charger.

RE: 12V to charge 24V system

How long did the battery last? I am glad that this failure was less violent and destructive than every Li battery failure that I have witnessed. My brother almost lost his hand when one basically went full Red-Giant while taking it off the charger.

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

RE: 12V to charge 24V system

(OP)
DC-DC converter is an isolation device and it prevent backflow. 12V starter battery connected parallel with DC-DC converter.
Im sorry cant attached the schematic but the connection is from the car alternator -> 12V car battery -> 12/24V DC-DC Converter -> 24V Lithium Battery. All the connection is in parallel.

Voltage across 12V battery is about 13.4V, which mean the 24V battery not backflow to the 12V battery. However, the odd is the input ampere for car battery is much lower that the output. The output ampere of car battery higher about 10A from it input. If this case protracted for more than 2 hours,can it harm the car battery?

Battery cannot last longer, from my experience only stand for less than 3 hours then the car battery will puffed-up.

Sorry im new in this forum, dont know how to include your comment in my reply.

RE: 12V to charge 24V system

3 hours to failure = you are doing something very bad to the battery, likely grossly over charging it. As already pointed out, a DC converter is not a charger so find a much better way to charge the battery.

RE: 12V to charge 24V system

What kind of battery is the failed battery?

The voltage seems like a lead-acid chemistry.

I have never seen a liquid lead acid battery puff up. If it is a gel-cell then those do not withstand over charging and should not be attached to an alternator. I doubt the lithium cell and voltage booster make any difference.

From https://www.batterystuff.com/kb/articles/battery-a..."

" If you are using an alternator to recharge a true Gel Cell a special regulator must be installed."

RE: 12V to charge 24V system

(OP)
I was using victron AGM battery, it also puffed-up.

Lead acid and AGM both of this battery were puffed up.

RE: 12V to charge 24V system

Is the "car battery" the 12V battery? You call it starter battery in one sentence, and apparently car battery in another.

Without a schematic, which was requested earlier, it sounds like the alternator, the 12V battery, and the DC/DC converter input are all connected together. When the car is running, the alternator is driving the DC/DC converter, which probably a really bad idea. It's likely that there's some interaction resulting in excessively high voltages being applied to the 12V battery.

TTFN
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RE: 12V to charge 24V system

romeo1990 - are you asking any questions or just sharing what happens when batteries are charged incorrectly?

RE: 12V to charge 24V system

24 volt and poor English skills? Sounds like something for NATO. All vehicles have to be able to jump or be jumped by 24v. I have a Chevy M1008 CUCV truck. Dual alternators, dual battery, 24 volt starting and 12v everything else. It's a terrible system but it works ok. Each alternator is 12v charges a battery. It keeps thr batteries relatively isolated so odd differences in capacity and charging characteristics don't matter and helps keep from smoking batteries. What it does smoke are glow plugs because it uses a resistor to drop voltage from 24 to 12. So when one glow plug fails it over-voltages the rest until they all fail.

RE: 12V to charge 24V system

3Dave, I see regular lead acid batteries puff up all of the time. As the plates fail the swell and bulge the case a bit. I work with the it's dead? Let's put it on the charger amd see what happens types. With any slight swelling of the case I can almost always tell them it won't work without even putting a meter on it.

RE: 12V to charge 24V system

I too have seen lead acid batteries swell. Every time, I was able to trace it back to an overcharging condition (typically a faulty voltage regulator on the alternator).

My understanding with lithium batteries is that excessive current results in the lithium actually plating the anode, eventually resulting in a short circuit condition between electrodes, breakdown of the cathode, and spikes in pressure and temperature.

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