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Very tiny dc to dc charger

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imbuere

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Hello, I'm in the process of building a larger system, but it's not going to be ready for a trip I have coming up this next week.

For this trip, I'll have a Battle born 12v/100 ah battery and a 40L fridge and maybe a heating blanket.

I won’t have a way to charge the battery, but I will be driving a TON (2,500 miles in 9 days). So I’m wondering if I could use something like the link below to keep the BB topped off during the trip. This would be powered from a cigarette lighter.

Best solution? I’m sure not, but something simple and cheap to rig? You tell me.

Adjustable Voltage Regulator DC, DROK Buck Boost Converter 6.0V-36V 9v 12v to DC 0.6-36V 24v 5A Power Supply Panel, Constant Current Volt Step Up Down Module
https://www.amazon.com/dp/B089ND7PTH/ref=cm_sw_r_awdo_7VP12GDBNMN3MGCX6YR3?psc=1

Thanks!
 
imbuere said:
Hello, I'm in the process of building a larger system, but it's not going to be ready for a trip I have coming up this next week.

For this trip, I'll have a Battle born 12v/100 ah battery and a 40L fridge and maybe a heating blanket.

I won’t have a way to charge the battery, but I will be driving a TON (2,500 miles in 9 days). So I’m wondering if I could use something like the link below to keep the BB topped off during the trip. This would be powered from a cigarette lighter.

Best solution? I’m sure not, but something simple and cheap to rig? You tell me.

Adjustable Voltage Regulator DC, DROK Buck Boost Converter 6.0V-36V 9v 12v to DC 0.6-36V 24v 5A Power Supply Panel, Constant Current Volt Step Up Down Module
https://www.amazon.com/dp/B089ND7PTH/ref=cm_sw_r_awdo_7VP12GDBNMN3MGCX6YR3?psc=1

Thanks!
Click to expand...
" max output current 5A" , so, if your 100Ah battery is at 50%, and you need to charge back the 50Ah missing, 50/5=10 hours (actually it will take a little more than 10 hours) to charge it back, if you don't have any load on the battery.
 
TEV said:
" max output current 5A" , so, if your 100Ah battery is at 50%, and you need to charge back the 50Ah missing, 50/5=10 hours (actually it will take a little more than 10 hours) to charge it back, if you don't have any load on the battery.
Click to expand...
Yeah, that makes perfect sense and exactly what I was expecting. I’d go a little higher, but I don’t want to stress the cigarette lighter.

Other than “this will take forever to fully charge the battery”, anyone see any drawbacks?
 
Make sure the converter can act as a battery charger and allow voltage to sag instead of overload when your battery wants 50+ amps.
To me it looks like a fixed voltage power supply that will overload. Confirm with the seller.
 
time2roll said:
Make sure the converter can act as a battery charger and allow voltage to sag instead of overload when your battery wants 50+ amps.
To me it looks like a fixed voltage power supply that will overload. Confirm with the seller.
Click to expand...
Good point. I figured it would just regulate current and only supply 5a at 13.8v. But if the battery asks for 50a, it has to give it, right?
 
TEV said:
Why don't you get a 10A one, the cigarette lighter plug should be ok.
Something like this: https://www.amazon.com/Automatic-Converter-10A-Regulator-Waterproof/dp/B089M5KYZM
Click to expand...

That's not designed to limit the max current at 10A, but to handle such load. I', 95% sure that this will overload and fail.

There are step-up/step-down CC (constant current) CV (constant voltage) convertors. It is a cheap option that will provide some safety and guarantee for the charging speed. But consider the fact that these are NOT battery charges. They will not terminate the charging under specific conditions, so to be on the safe side you should go for no more than 3.45-3.5V per cell.

I was planning to use CC CV modules in the past for a similar case, but with lead-acid secondary battery. I did the math and the 2nd battery internal resistance and the wire resistance were limiting the charging current to 25A in the worst-case scenario. I went for fuses, DIY Voltage Sensitive Relay and 6mm2 wires between the two batteries. This worked flawlessly for 2 years when I sold the car. But I would not recommend this approach for LiFePo4 secondary battery.

The best option is to go with DC to DC battery charger. Victron Orion series is an example. They are not cheap, but if you plan to use this approach for charging the second battery in the future it will pay off.

Edit: Check the specs for the Victron Orion if you are going for it. I have some doubts that it may just be an adjustable CC CV module.
 
Last edited:
imbuere said:
Good point. I figured it would just regulate current and only supply 5a at 13.8v. But if the battery asks for 50a, it has to give it, right?
Click to expand...
Not exactly...
It says it has over-current protection, but I'm not sure you can count on it...
What you need is a CC/CV charger.
The first model you mentioned has this. About the second one I'm not sure.
Also, it's recommended not to run these things at full load. The second one has no adjustments, so basically it will run at full load untill your battery is almost full (at least for the set voltage).

Even with the first model, I wouldn't run it at 5A, as it will probably heat up quite a bit.

I have a stronger model step down also from DROK, that can theoretically pump out 20A, but running it above 15A is pushing it (fan goes on like crazy and the whole thing get fairly hot).
 
I can spend a little… especially since I’ll need this in the long run. How about this:
Victron Energy Orion-Tr Smart 12/12-Volt 18 amp 220-Watt DC-DC Charger, Isolated (Bluetooth) https://www.amazon.com/dp/B0851TPKV...t_i_5667EKRSK0NKZ0D5MSF0?_encoding=UTF8&psc=1

It should still be able to run off my cigarette lighter (fuse is 20 a) until I get it hard wired… just dont have that time before I leave.

I wan isolated, correct?
 
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imbuere said:
I can spend a little… especially since I’ll need this in the long run. How about this:
Victron Energy Orion-Tr Smart 12/12-Volt 18 amp 220-Watt DC-DC Charger, Isolated (Bluetooth) https://www.amazon.com/dp/B0851TPKV...t_i_5667EKRSK0NKZ0D5MSF0?_encoding=UTF8&psc=1

It should still be able to run off my cigarette lighter (fuse is 20 a) until I get it hard wired… just dont have that time before I leave.

I wan isolated, correct?
Click to expand...
18 amp output could be 25 amp input depending on the voltage boost necessary. Check the manual.
 
time2roll said:
18 amp output could be 25 amp input depending on the voltage boost necessary. Check the manual.
Click to expand...
Ah, you’re right. I just ordered the 9 amp one. It’s only $67… but not Bluetooth. Oh well, I guess it can’t hurt to have one around as a backup.
 
imbuere said:
Ah, you’re right. I just ordered the 9 amp one. It’s only $67… but not Bluetooth. Oh well, I guess it can’t hurt to have one around as a backup.
Click to expand...

Do you have the unit/brand/model or web link to this 9 amp version? Guessing it outputs 14.6?
 
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