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Charge eBike battery questions

Momar89

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Mar 21, 2023
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New York, NY
Hi all,

I am looking to charge an eBike battery (36V / 13Ah / 468Wh) using its charger (36V/2A). Initially I was looking at buying a pre-made power station like Jackery/EcoFlow but stumbled onto DIY Solar Forum as I went down the rabbit hole.

Question - Instead of charging a battery to charge another battery, could I just buy an MPPT Controller, inverter, and solar panels and charge the bike battery directly?

Thanks!
 
Hi all,

I am looking to charge an eBike battery (36V / 13Ah / 468Wh) using its charger (36V/2A). Initially I was looking at buying a pre-made power station like Jackery/EcoFlow but stumbled onto DIY Solar Forum as I went down the rabbit hole.

Question - Instead of charging a battery to charge another battery, could I just buy an MPPT Controller, inverter, and solar panels and charge the bike battery directly?

Thanks!

Assuming it's a "dumb" charger that only provides a voltage and current, the battery has a built-in BMS, and you have a complete handle on the charging parameters, then yes - with a Victron. The smallest you could use is the SmartSolar 100/20 with the 48V option, which can also operate at 36V.

You would need to connect the Victron to the e-bike battery first to establish the battery operating voltage and configure the charge parameters for the battery. From that point forward, you could just reconnect the charger to the battery whenever charging was needed and solar was available.
 
The Victron 100 | 20 is a fantastic bang for your buck. You'll need to use the app via Bluetooth to set the 36v option, but you can also control charge cutoff by voltage and max charging amps. Most e-bike batteries are 18650 trash with no BMS so you really need to be careful about overcharging or throwing too many amps at them.

You connect the panels directly to the MPPT PV input, and for a 36v battery you'll need a minimum of 41-42v (Vbatt + 5v) to *start* the charging (Vbatt + 1v thereafter). This may require two panels in series, depending on the VOC of the panels. Then you connect the battery directly to the MPPT battery output - you can use something like an XT60 connector. No additional battery / inverter required.
 
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In my proposal, you're charging the battery direct with solar.

If you go your route and get an inverter, then you could get away with a 75/15, connect it to a 12V battery to configure the charge controller. Then the charge controller could power the inverter directly; however, you would likely want to go with 200W of panels whereas you could get away with 100W with the direct charge option.
 
Thank you Momar89 for asking this question!

I am researching this very idea, avoiding looking like a fool by reading instead of jumping out and posting.

An inverter will give you several other capabilities, and may provide a smoother experience, given the fluctuation of our sun´s output, thinking.

Member The Good Package sounds much more knowledgeable than myself and sunshine_eggo has proven it repeatedly, yet if you go without an inverter that 100W you could get away with would need to be a series of panels that will be some amount higher than the voltage of your ebike battery pack; quite a bit higher than nominal 36V? What is the charging voltage of your AC charger? I did not see it in your link.

For example, my AC (72V) ebike battery charger is 84V at 5A and will terminate on its own. Not sure of the charging algorithm.

Going with the inverter setup supplying the ´authorized´ charger may be prudent in case open flames ensue, and blame is being assigned.
 
Thank you Momar89 for asking this question!

I am researching this very idea, avoiding looking like a fool by reading instead of jumping out and posting.

An inverter will give you several other capabilities, and may provide a smoother experience, given the fluctuation of our sun´s output, thinking.

Member The Good Package sounds much more knowledgeable than myself and sunshine_eggo has proven it repeatedly, yet if you go without an inverter that 100W you could get away with would need to be a series of panels that will be some amount higher than the voltage of your ebike battery pack; maybe higher than nominal 36V? What is the charging voltage of your AC charger? I did not see it in your link.

For example, my AC (72V) ebike battery charger is 84V at 5A and will terminate on its own. Not sure of the charging algorithm.

Going with the inverter setup supplying the ´authorized´ charger may be prudent in case open flames ensue, and blame is being assigned.

The "official" e-bike battery charger you have may have a predetermined cutoff voltage, which is very important. The primary cause of e-bike battery fires is leaving the charger on for too long (overnight). The benefit of charging directly from a Victron MPPT is that you can specify the charge cutoff voltage to prevent overcharging.

Adding a battery and inverter to the mix creates a substantial additional expense, but yes you do have a lot more flexibility to charge other devices. In that case I would recommend a pre-built power station. These have a built-in SCC and you can find 300W / 500-ish watt hour models for the cost of the Victron MPPT SCC alone. Having at least a 300W model ensures you can run 150W indefinitely. My rule of thumb for continuous load is ~50% of max stated watts (not surge) for all Chinese inverters.
 
Thanks for the quick response! It is this type of charger

So I can wire Solar Panels to the Victron 48V MPPT and then wire that to an inverter like this? I don't need a second battery to run the inverter, right?

That's a "4 pin" charger. Not sure what the implications are. I suspect two pins are for the main power, and the other two might be a signalling circuit for the BMS to tell the charger to shut off. Without knowing more about the charger, I would be hesitant to replace it.
 
Regarding 4 pin: my charger has that, and the battery supplier sent an adapter that converts to a 2 conductor XT60. There is an XT90 that goes to the ebike controller brain, and to the rear hub.
 
Is it possible to send power directly from a charge controller to an inverter, as Momar89 asked?

If you go your route and get an inverter, then you could get away with a 75/15, connect it to a 12V battery to configure the charge controller. Then the charge controller could power the inverter directly; however, you would likely want to go with 200W of panels whereas you could get away with 100W with the direct charge option.
 
For the sake of discussion that takes into consideration flexibility, lets say the bike got trashed, or stolen. Yet the battery pack is still in hand. Could Momar89 in turn use that same Victron charge controller, adjusting the settings for the voltage of the battery pack, and use that electrical storage to power an inverter for other uses? Could a pre-built power station fit into that scenario when out in the field?
 
For the sake of discussion that takes into consideration flexibility, lets say the bike got trashed, or stolen. Yet the battery pack is still in hand. Could Momar89 in turn use that same Victron charge controller, adjusting the settings for the voltage of the battery pack, and use that electrical storage to power an inverter for other uses? Could a pre-built power station fit into that scenario when out in the field?

The battery *may* be able to function as a standalone unit, depending on the internal circuitry and wiring. Most DIYers would crack open the battery and harvest / repurpose the cells. If it would work as a standalone then you could build a portable rig. I'd probably use a 36v to 12v step down converter and run a cheaper 12v inverter, cigarette lighter charger, usb charger, fan, etc. Plus, 12v inverters are much cheaper and easier to find than 36v.

But again, you're approaching (probably exceeding) the cost of a prebuilt power station with similar watt hours. Personally, I would harvest the cells and build some portable power banks. If they are 18650 cells then they sell battery boxes (link below) that hold 16 cells. I have a few of them filled with capacity-matched 18650 batteries harvested from old laptop batteries.

 
Question - Instead of charging a battery to charge another battery, could I just buy an MPPT Controller, inverter, and solar panels and charge the bike battery directly?

Thanks!
A family member wants me to build him an "off grid" EV charging station that is pure PV. Sure. I can do that. But the money you're going to spend making that stable (needs batteries) and sustainable (needs more batteries) will vastly exceed doing it the "simple" way. What you want is the same thing, just way scaled down. You might get away with no batteries if you're willing to have the scooter down for days at a time due to lack of sun.
 
The "official" e-bike battery charger you have may have a predetermined cutoff voltage, which is very important. The primary cause of e-bike battery fires is leaving the charger on for too long (overnight). The benefit of charging directly from a Victron MPPT is that you can specify the charge cutoff voltage to prevent overcharging.

Adding a battery and inverter to the mix creates a substantial additional expense, but yes you do have a lot more flexibility to charge other devices. In that case I would recommend a pre-built power station. These have a built-in SCC and you can find 300W / 500-ish watt hour models for the cost of the Victron MPPT SCC alone. Having at least a 300W model ensures you can run 150W indefinitely. My rule of thumb for continuous load is ~50% of max stated watts (not surge) for all Chinese inverters.
Thanks for the recommendation. I thought most power stations wouldn't be adequate to charge the bike battery. For instance, the Jackery 500 has 518 watt-hour (24Ah, 21.6V) capacity, so considering the eBike battery is 13Ah / 468Wh, I would get one eBike battery charge out of the Jackery with a little bit of Jackery battery life left over?
 
Thanks for the recommendation. I thought most power stations wouldn't be adequate to charge the bike battery. For instance, the Jackery 500 has 518 watt-hour (24Ah, 21.6V) capacity, so considering the eBike battery is 13Ah / 468Wh, I would get one eBike battery charge out of the Jackery with a little bit of Jackery battery life left over?

You could be recharging the power station via solar at the same time. But yes, that would be the bare minimum size of power station I would consider for this use case.
 
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