Using 12V lead acid to charge 36V/10ah lithium ion

[Robmc]

Firstly hello to everyone an thanks in advance for all your help.

I want to charge a 36V lithium ion ebike battery with 3 x 12 volt standard lead acid batteries which will be wired to give 36v.

My question is. Is this feasible and what type of 12V batteries would be best for this task.

Also what amp per hour 12V batteries should I buy and will I need some sort of regulator between the 12V setup and the lithium ion battery.

How long will it take for the 12v setup to charge the lithium ion.

Lots of questions but thanks again in advance.

 

[Mtl_Biker]

Many (most?) ebike chargers have some circuitry in them to prevent over charging and to do uh, other stuff. I'd be real careful with what you plan to do.

Another option, maybe safer, would be to get an inverter so that you could supply your bike's charger with the right voltage. (Sydney uses 220v?? Assuming Sydney Austraila and not Nova Scotia.)

How do you plan to charge your 3 12v batteries?

 

[Robmc]

Hi Mtl
Yes I am in Sydney, good spot.

I am planning on charging the 3 x 12 volt with solar.

I am really looking for the most cost effective and simple/robust way of setting up a solar power bank for
an ebike.

So I though, solar panel (12v x 3), to solar controller, to feed 3 x 12v lead acid batteries wired to give 36v. Then have another controller to manage the charge from 36v lead acid to the 36v lithium ion.

My other option is to remove the lead acid batteries from the equation and have a 36v lithium ion as the battery bank.

Sorry I was just asking the question peacemeal rather than all in one go.

 

[Mtl_Biker]

Hi Mtl
Yes I am in Sydney, good spot.

I am planning on charging the 3 x 12 volt with solar.

I am really looking for the most cost effective and simple/robust way of setting up a solar power bank for
an ebike.

So I though, solar panel (12v x 3), to solar controller, to feed 3 x 12v lead acid batteries wired to give 36v. Then have another controller to manage the charge from 36v lead acid to the 36v lithium ion.

My other option is to remove the lead acid batteries from the equation and have a 36v lithium ion as the battery bank.

Sorry I was just asking the question peacemeal rather than all in one go.

While I'm sure there are some folks on this forum who are wizards with electronics, I can't help thinking that your question might be best posed in some kind of electronics/solar forum. But I hope one of the gurus here will be able to help.

Perhaps you should mention which bike/battery you have, as just 36v lithium ion ebike battery may not be specific enough. It's my understanding (I'm NO expert!) that some battery units have some kind of circuit with them that their specific charger needs and/or looks for. I don't think it's as simple as just connecting positive and negative leads.

Is your solar system going to be specifically for the e-bike battery or do you have other things on your grid? Is your whole house solar powered?

Take a look on the intro section of this forum... a few days ago there was a new member claiming to have the first solar powered e-bike. Turned out he was only using solar to charge his e-bike battery. (Sort of like saying he's got a solar powered drill.) But he may be a source of good information on how to use the solar to do what you want.

Best of luck!

 

[sl_duck]

Keep it simple. Get one 12v battery and charge it with the solar panels using a charge controller. Then get a small 100w 12-120v inverter to supply your regular ebike battery charger. You will lose a bit of energy in the conversions, maybe 10%, but it'll all be off-the-shelf components which have some built in safeguards, especially the ebike charger.

charging to the 12v battery is a good idea because it can charge during the day while you are away from it, then transfer that energy into the ebike overnight when you are home.

BTW, a 36v lithium ion battery is nominal 36v. Charge voltage is 42v.

 

[Robmc]

Hi Mr Duck
I see exactly what you mean and understand re the off the shelf components.

So a simple solar panel that produces 12V energy, with a solar controller going to one larger standard 12V battery. Then a standard inverter similar to what you would use the run 240v device from a car but I will plug my ebike charger into it.

Simple and elegant. Nice work. My next question is. If my ebike battery is 10ah and I am running a 1.5ah charger, what size 12V battery should I get and what size panel. I know biggest is best but I want to tuck it away inside a column at home.

Thanks for your help in steering me in the right direction.

Thanks
Rob

 

[sl_duck]

Hi Rob,
Since there's different voltages at each stage, it's easiest to work in watt-hours (Wh).
Your bike battery is 10ah at 36v nominal, so 360Wh
check the nameplate on your charger to see it's maximum output (likely 2A @ 36v, so 72w). That's your minimum inverter size.
If you plan on completely recharging the ebike each day, take the 360Wh and divide by 12v to get 30Ah. That's the minumum lead-acid (we'll call it house battery) size you'll need. Probably wise to add about 20% to that, to cover losses and lower than rated performance. You can connect a few smaller batteries in parallel if size and shape is a factor.

Solar panels are rated in watts (the actual raw output is about 17v). Take your expected hours of direct, intense sun per day and multiply it by the power rating to get the Wh output of your panels. That has to be greater than 360Wh for your purposes. If you can expect 10hrs per day of great sun, you'd need a minimum 36w panel. In reality you will not get great sun every day, the panels won't be perfectly oriented, and you'll have some losses from the controller, so I would at least double that.

That's the quick-n-dirty calculations. There's certainly room to make it all more efficient, but if you're just experimenting and learning, go with what's cheaply available. If you're serious, it's always wise to overbuild capacity (i.e. I'd use a 100w solar panel, 100ah house battery because those sizes are quite common and you'll have more flexibility)
One thing to watch out for is that cheaper inverters use a "modified sine wave" output. Sometimes computer and ebike chargers won't work with that. Try to get an inverter that is "pure sine" output to avoid that risk.

Good luck with your project! One thing you may realize is that power from a wall outlet is incredibly cheap vs generating your own.

 

[Mtl_Biker]

Hi Rob,
Since there's different voltages at each stage, it's easiest to work in watt-hours (Wh).
Your bike battery is 10ah at 36v nominal, so 360Wh
check the nameplate on your charger to see it's maximum output (likely 2A @ 36v, so 72w). That's your minimum inverter size.
If you plan on completely recharging the ebike each day, take the 360Wh and divide by 12v to get 30Ah. That's the minumum lead-acid (we'll call it house battery) size you'll need. Probably wise to add about 20% to that, to cover losses and lower than rated performance. You can connect a few smaller batteries in parallel if size and shape is a factor.

Solar panels are rated in watts (the actual raw output is about 17v). Take your expected hours of direct, intense sun per day and multiply it by the power rating to get the Wh output of your panels. That has to be greater than 360Wh for your purposes. If you can expect 10hrs per day of great sun, you'd need a minimum 36w panel. In reality you will not get great sun every day, the panels won't be perfectly oriented, and you'll have some losses from the controller, so I would at least double that.

That's the quick-n-dirty calculations. There's certainly room to make it all more efficient, but if you're just experimenting and learning, go with what's cheaply available. If you're serious, it's always wise to overbuild capacity (i.e. I'd use a 100w solar panel, 100ah house battery because those sizes are quite common and you'll have more flexibility)
One thing to watch out for is that cheaper inverters use a "modified sine wave" output. Sometimes computer and ebike chargers won't work with that. Try to get an inverter that is "pure sine" output to avoid that risk.

Good luck with your project! One thing you may realize is that power from a wall outlet is incredibly cheap vs generating your own.

Super reply there, Duck!!!

 

[PDXzap]

There are charge controllers that are designed to charge lithium.
You have inefficiencies going from the DC from the solar panel to the storage battery, then from the storage battery to the inverter, then losses from the inverter going from DC to AC to your charger.

Google "lithium 36v solar charge controller".
Here's one: https://www.electriccarpartscompany...h-Power-br-Solar-Charge-Controller_p_156.html

FYI, I've never tried any direct solar charging for lithium.

 

[sl_duck]

There are charge controllers that are designed to charge lithium.
You have inefficiencies going from the DC from the solar panel to the storage battery, then from the storage battery to the inverter, then losses from the inverter going from DC to AC to your charger.

Google "lithium 36v solar charge controller".
Here's one: https://www.electriccarpartscompany...h-Power-br-Solar-Charge-Controller_p_156.html

FYI, I've never tried any direct solar charging for lithium.

Nice, and cheaper than I would've expected.
You have to be very familiar with your pack max charge specs before trying to charge from another source though, or results may range from tripping the protection to creating an impressive fireball.
I agree the multiple conversions, especially to 220v and back down, are not ideal but the benefit is there is little risk of frying anything, and no rewiring of connectors to accommodate the pack. I got the impression Rob is new to this kind of project.