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12v charging for 48v battery?

Posted: Sep 11 2019 10:21am
by WaltherDawg
I have two options, first is a 400w inverter powering the charger the second is wiring a 12v boost converter (I can crank it up as far 60v) and charging it from that.
Is the boost converter a legitimate option? If yes what voltage and amperage should it be set at?
Battery is a UPP 48v 20ah.

Oops, it is a Joyisi battery.

Re: 12v charging for 48v battery?

Posted: Sep 11 2019 11:23am
by john61ct
Link to battery seller listing, data sheet if possible. Ideally you know whether 13S or 14S, and what cells were used.

Do you care enough about longevity to get a DMM & ammeter and learn how to optimize?

Going through an inverter, DC to AC to DC will have efficiency losses.

What is the actual energy source, alternator while driving, are you off grid for long periods? Do you have a solar setup?

Are you always charging from DC or only sometimes?

The converter (link please) needs to be current limited, and cheap Chinese should be operated **well** below claimed amps rating.

Anything not listed as a charger means **you** need to determine the stop-charge point, if you let it go too long or something fails at best bad for longevity, worst case a bad fire!


Re: 12v charging for 48v battery?

Posted: Sep 11 2019 1:52pm
by WaltherDawg
Link to battery seller listing, data sheet if possible. Ideally you know whether 13S or 14S, and what cells were used.
A. Battery. https://smile.amazon.com/gp/product/B07 ... UTF8&psc=1

Do you care enough about longevity to get a DMM & ammeter and learn how to optimize?
A. Not familiar with this but willing to learn.

Going through an inverter, DC to AC to DC will have efficiency losses.
A. Understood, one reason looking for alternatives

What is the actual energy source, alternator while driving, are you off grid for long periods? Do you have a solar setup?
A. Automotive 12v, AKA 14.4v

Are you always charging from DC or only sometimes?
A. Will use standard AC charger when possible. DC charging for when transporting in vehicle.

The converter (link please) needs to be current limited, and cheap Chinese should be operated **well** below claimed amps rating.
A. Drok (chinese I think) https://smile.amazon.com/gp/product/B07 ... UTF8&psc=1

Anything not listed as a charger means **you** need to determine the stop-charge point, if you let it go too long or something fails at best bad for longevity, worst case a bad fire!
A. Could I lower the charge voltage and it self limit? I can adjust the charge voltage and amperage to whatever would work best.

Sorry about not hot linking, haven't learned how to do that here yet.

Re: 12v charging for 48v battery?

Posted: Sep 11 2019 8:51pm
by john61ct
54.6v so 13S

Mains charger only 3A so 5-6hours if not depleted all the way.

At that rate 53V would be ideal for longevity, 54.0 at most (CC-only) for faster charge higher currents.

Max 10-12A rate or 600W will take a couple hours, higher will reduce longevity a bit.
WaltherDawg wrote: Automotive 12v, AKA 14.4v
OK, but you will need a thousand kWh of energy input, you need to plan for an actual source.

Are you driving for 2 hours and charging off the alternator every charge cycle? You don't want to drain your car battery, won't be enough anyway.

A genset might be worth it if going off grid frequently.

Or piles of solar panels? But then you likely need a buffer bank or you can only ride at night 8-)


> Are you always charging from DC or only sometimes?
A. Will use standard AC charger when possible. DC charging for when transporting in vehicle.

I meant how often, just a few weekends per year, or full time?

> A. Drok (chinese I think) https://smile.amazon.com/gp/product/B07 ... UTF8&psc=1

Stick to 10A should be OK. Do not draw off your car battery unless supported by charge input

> **you** need to determine the stop-charge point, if you let it go too long or something fails at best bad for longevity, worst case a bad fire!
A. Could I lower the charge voltage and it self limit? I can adjust the charge voltage and amperage to whatever would work best.

No, follow the profile I gave above, watch voltage at the battery rise, stop when it hits. That's CC charging. For precision, like benchmarking holding Absorb/CV gets more complicated, no reason for that in normal usage.

For CC+CV charging, or to analyze the way your charger works, you need an ammeter. Included in a coulomb-counter if you want see your Ah transfer totals.

Re: 12v charging for 48v battery?

Posted: Sep 12 2019 12:27am
by amberwolf
john61ct wrote:
Sep 11 2019 8:51pm
OK, but you will need a thousand kWh of energy input, you need to plan for an actual source.
I think you are off by a few decimal places there. ;)

A "48v" 20Ah battery is only around 1000Wh (1kWh).

Re: 12v charging for 48v battery?

Posted: Sep 12 2019 11:56am
by john61ct
Lol, yes meant 1kWh, or 1000Wh, not both.

Still, lots more than anyone should consider pulling from a Starter batt without concurrent charge input of at least say 80% of the watts being transferred to the secondary battery.

So if the Drok is charging at 500W, the alternator (or solar-fed bank) should be capable of supplying around 30A minimum, so only say 15-20Ah are drawn from the Starter batt.

Otherwise you may well end up stranded out there, and if done repeatedly, will quickly need to buy a new Starter.

Re: 12v charging for 48v battery?

Posted: Sep 12 2019 1:14pm
by WaltherDawg
Planning on using vehicle power only when the engine is running. Mainly so I can recharge it while I am driving to next destination.
So, if I get this right.
1. Stop charging when battery voltage reaches 53v, at most 54v.
2. Set max amperage through boost converter at 12a or less, 3a would work well if I have enough charge time available.
3. Solar is a different animal entirely. IF I did solar then I would set it up to charge a battery bank and then charge from that. Weight is not a problem here, all this equipment would be carried by a truck and/or an RV.

Re: 12v charging for 48v battery?

Posted: Sep 12 2019 3:21pm
by kcuf
boost converter current will vary

across pack charging curve

max amp setting often limited

within narrow voltage span



simple effective numerous choices

12vdc inverter to 120vac

back to whatever dc required



some losses yeah

big deal ?

not here

Re: 12v charging for 48v battery?

Posted: Sep 12 2019 9:49pm
by john61ct
WaltherDawg wrote:Planning on using vehicle power only when the engine is running. Mainly so I can recharge it while I am driving to next destination.
So, if I get this right.
1. Stop charging when battery voltage reaches 53v, at most 54v.
2. Set max amperage through boost converter at 12a or less, 3a would work well if I have enough charge time available.
3. Solar is a different animal entirely. IF I did solar then I would set it up to charge a battery bank and then charge from that. Weight is not a problem here, all this equipment would be carried by a truck and/or an RV.
Yep. Alt output at idle, lower amps, driving go up.

3A is 6+ hours

Test the Drok on a bench for heat rise at 12A, 8-10 likely safer, also put a fan on it.

And buy a spare.

Save pennies for proper DCDC charger one day, and go to 2x 7S pack in future, 52V nominal 58V charging.