charging 36v from 12v

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xadmx

1 kW
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Feb 18, 2013
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339
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i am going to make 2 small ebikes for a camper van, but i want to run them at 36v so they have a bit of power.
what do you think the best way to charge them from 12v would be. do you think it would be best just to use a 12v inverter to 240v then to a 36v charger iam in the uk so 240v, or do you think something like below would be ok. thanks


https://www.ebay.co.uk/itm/DC-DC-Step-Up-Boost-Converter-600W-12V-60V-to-12V-80V-Power-Supply-Module-Board/283554552510?hash=item42052b1abe:g:bhUAAOSwn-pdMtdn
 
LI batteries other than LFP are very dangerous, keep them outside the living space, or convert to LFP.

Best to have a unit that will automatically **stop** charging when full rather than relying on your memory / attention.

But also, do supervise charging as closely as possible, do not leave unattended.

And current limiting is a must.

Inverting in between is wasteful of energy, but some setups can afford that.
 
That would work, and be quite a bit more efficient than an inverter/charger setup. Set it to output 42V if you want to fully charge a 36V pack. The BMS on the battery will provide an extra layer of protection should it put out too much voltage for some reason.

Plenty of people have used these for charging, I've never heard about a problem other than they die if you run them close to their rated power.

So you'll want to reduce the current so that it's putting out about 300W, half it's rated power. That should avoid overheating it and make it live a longer life and you probably shouldn't be charging the battery much faster than that anyway. Maybe even slower depending on the specs of the particular battery.

Maybe buy 2 and have a spare on hand.

Edit: Just looked again, and it's limited to 15A on the input side, so at 13.5V that's only 200W or so. I'm not sure if that's limited automatically by the circuit, or just the fuse.

So you might need to lower the output current setting to avoid blowing that fuse.

If you set it to 4A output, and voltage to max out at 42V, that's 168W max power which should leave some headroom in case the input voltage drops (which will increase the input current accordingly).
 
dustNbone said:
So you'll want to reduce the current so that it's putting out about 300W, half it's rated power.
Click to expand...

Probably not necessary if he is charging from a 12v supply. The maximum input current is 15 amps. Assuming the nominal 12v supply is actually 14v, his maximum output watts are a bit less than 210.
 
I'd consider this unit for its additional fan and display. It will probably be easier to set up.

https://www.ebay.co.uk/itm/DC-DC-BST900W-CNC-Boost-Converter-8-60V-Step-up-10-120V-Solar-Charging-CVCC-UK/153068342791?hash=item23a3958e07:g:7NsAAOSwPTlbKdGU
 
Hwy89 said:
Wouldn't it be simpler to just run an RC balance charger straight off the 12VDC
?
Click to expand...

That's a good idea. You can get about 300 watts charging output in the $60-70 U.S. range and it will come with built-in metering, fan and a neat and tidy package. It will cost a bit more, but the cost isn't outrageous.
 
use similar schemes here


dc converters do work

sometimes tricky current limiting load side



36v rc can be difficult to source

i travel with small 106B

helps touching up few cells



automotive inverter often easiest 12vdc to VAC line supply

likely already have VAC bulk charger
 
kcuf said:
36v rc can be difficult to source
Click to expand...

Good point. I forgot that mine will do a 36v battyer, but it is a 10s icharger and that runs over $100. The typical 6s units probably don't have the necessary output voltage.
 
iCharger 4010-Duo from Junsi

FMA CellPro line, Hyperion, ISDT are also decent quality

Graupner Polaron, top-notch but pricey
 
john61ct said:
iCharger 4010-Duo from Junsi

FMA CellPro line, Hyperion, ISDT are also decent quality

Graupner Polaron, top-notch but pricey
Click to expand...

They seem a bit higher in price than £8.99.
 
I think it really comes down to how often it's going to be used. If it's a one time trip thing, an inverter and AC charger is not a terrible option, assuming you have the ability to charge your 12V system the efficiency hit isn't such a big deal.

If this RV is going to be used by ebikers on a regular basis, over many years, a built in efficient charging system is probably what you want. Space is almost always at a premium when you're on the road, a DC converter (or two) could be mounted tidily in the battery space, with a bit of cable that could be stored in there and pulled out for charging when needed. The rest of the time it's out of the way, which is very valuable in any constrained space.

After thinking about it a bit, I'm going to do this to my RV, it seems like a pretty worthy $15 upgrade.
 
Bump the battery up to 12s which will still work on most 36 volt controllers. Then split the 12s packs into 6s halves which can be charged in parallel on a common RC balance charger. I've been doing it that way for years. I also bring along a Meanwell power supply for those times when I have access to grid power and can grab a quick bulk charge.
 
Hwy89 said:
Bump the battery up to 12s which will still work on most 36 volt controllers. Then split the 12s packs into 6s halves which can be charged in parallel on a common RC balance charger. I've been doing it that way for years. I also bring along a Meanwell power supply for those times when I have access to grid power and can grab a quick bulk charge.
Click to expand...

How is that easier than setting a couple of pots, mounting a converter and forgetting about it?

Splitting a pack to charge it sounds like a hokey solution at best.
 
Hwy89 said:
The safety factor of using a charger that monitors individual series voltages and has an automatic shut down.
Click to expand...

But that isn't easier.
 
Could be just about as easy as bulk charging if the packs are built to be charged by two of those RC chargers simultaneously; the chargers just have to be isolated so they can be seriesed.

A few builds here on ES (primarily those using RC LiPo) are designed so the battery doesn't have to actualy be split or disconnected or antyhing, it's already prewired to just plug in a single connector (just like bulk charging) that contains the main and balance leads from both chargers. I was going to do this myself for my non-BMSed EIG NMC pack back on CrazyBike2, but ended up not needing to because it stayed balanced. I would've done it on the RC LiPo pack I used at the time, but never got around to it.
 
https://www.youtube.com/watch?v=dcU8Xz4Zh7w

instead of plugging in the solar panel, plug it onto the battery of the car.

Note that these are GREAT https://www.ebay.com.au/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=600W+DC-DC&_sacat=0

and with three of them (need to set each up with its own monitor to set up so each is doing similar work then forget)
I set them up to run at around 300W and mounted on a board x 3 and with a fan blowing over them.
step 1 set output voltage
step 2 set output current
disconnect
set up the other units you have one at a time
connect them all in parallel
charge away!

same unit will work on a solar panel directly connected, even in varying light conditions.

This rig charging a 14S to 58.8V is a fair jump in voltages and of course whilst a 5x step up should be 15Ain = 3A out the reality is significantly worse with more like 2.3A out.

NB: 3 or 4 connected together will flatten a car battery in a matter of 15mins hence only use with engine running!

Cheers KArl
 
Why the focus on "easy"? Better to do it right.

Review my #2 caveats.

A boost converter is fine, but the cheap-Chines ones should be used at half their rating or less.

To get reliability in high currents you need to spend more.

What is your actual energy input source?

Boost conversion is wasteful if you're using solar.

How quickly do you want to recharge the bikes?

Consider putting in a House bank at say 48V much larger than your total ebike pack capacities, convert **down** for 12V House circuit usage, and also down, but with much less of a voltage gap to charge the ebikes quickly and at least more efficiently.
 
john61ct said:
Why the focus on "easy"? Better to do it right.
Click to expand...

No focus on easy. It is just one of many considerations.

As for doing it "right", I agree with John61ct on erring on the side of extra capacity. I'd suggest spending a bit more on a higher rated converter that has a cooling fan. I've been running my bike using one of these and they seem to work very reliably at a regular input of about 15-20 amps from a 36 volt battery to step up to 54 volts. I did kill one of these in 9000 miles of riding. But the best guess on the reason was a bad connection upstream of the converter. The 95% or so efficiency seems about right in my experience. Maybe stepping up from 12-14v to 41-42v won't be quite as efficient. But the supplier claims 92% as the worst case.

https://www.ebay.co.uk/itm/1500W-30A-DC-DC-Boost-Converter-Step-Up-Power-Supply-Module-Electric-Unit-M-R6I7/282549875591?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D59535%26meid%3Df7e99646b04f45bab7ca9e1b990fe5ce%26pid%3D100005%26rk%3D3%26rkt%3D12%26sd%3D173961453415%26itm%3D282549875591%26pmt%3D1%26noa%3D0%26pg%3D2047675&_trksid=p2047675.c100005.m1851
 
I'd tend to agree. 12 to 42 I'd ballpark it between 80 and 85. Easy enough to measure though, I have a couple of the 600W ones on the way.

As for converting 48V down to 12 for the RV loads, some of them are quite substantial so you'd have to have a pretty beefy converter for that, depending on what equipment the RV has. Water pumps and furnace fans come to mind.
 
Yes not standardizing on a single system voltage will be more expensive, less reliable and less energy efficient no matter what.

But if necessary, then the backbone should be the higher one, wiith POL conversion downward.
 
Walked back in the thread, and yes I'd lost track of the use case, crossed wires with another thread EV pack powering a skoolie.

In this case, yes House at 12V, upconvert for charging the ebikes.
 
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