Repurposing An Ebike 72v SLA Battery Pack

[dragon]

Now that I’ve replaced my bike’s SLA batteries with a LifePo4 battery pack, I was thinking of repurposing my old batteries as a a big battery bank to charge small electronics; phones, bluetooth speakers, portable usb battery banks, etc. while in the garage. I do have a 100w 12v solar panel with a built-in controller that I’m planning to charge the pack with. I’m not too concerned with charging time efficacy as I’m kinda looking at this as an experiment I’d like to try.
I have the 6 - 12v 22ah batteries & a box to house the batteries in. I’ve come up with 2 options;

A) Wire a few or all 6 batteries in parallel so I’d have a 12v with 44 to 132ah pack & then use a 12v usb converter to charge various items.

B) Wire all 6 batteries in series so I’d have a 72v 22ah battery pack. Going this route I’d use my old 72vdc-12vdc converter from the ebike & a 12v usb converter to charge various items. Going this route I figure I’d need a MPPT Solar Panel Charge Controller to connect my 12v solar panel to the 72v battery pack to charge.

Any suggestions or advice to complete the experiment or should I just post the batteries for sale on the local kijiji/craigslist?

 

[harrisonpatm]

Repurposing is a great idea.

Go with all the 12v batteries in parallel, you're going to be limited by your solar panel's voltage. You say it's already regulated/controlled for 12v, find the specific output voltage to make sure you're not overcharging your battery bank.

The main reason you won't want to use a 72v bank is that stepping up your 12v panel to 72v is going to be rather inefficient. Possible, but a ton of losses. Plus, I'm assuming this bank is going to be hanging out in your house, and you won't have to worry about accidental zaps from 72v; 12v is much safer. Just keep your wires short as you can to reduce losses.

12v, 132ah, you're looking at about 1.5kwh of storage. Phones, speakers, ect, are great, but those are going to be using like 5-10w each. Not much. If you're going to go through the trouble of setting up a mini solar system in your house, consider getting the full use out of it. I have my mini system powering one full room of my house, direct dc, no inverter: room lights, all USB charging, router, modem, tablet, computer, speakers, in addition to charging my motorcycle. It's lovely.

 

[dragon]

Repurposing is a great idea.

Go with all the 12v batteries in parallel, you're going to be limited by your solar panel's voltage. You say it's already regulated/controlled for 12v, find the specific output voltage to make sure you're not overcharging your battery bank.

The main reason you won't want to use a 72v bank is that stepping up your 12v panel to 72v is going to be rather inefficient. Possible, but a ton of losses. Plus, I'm assuming this bank is going to be hanging out in your house, and you won't have to worry about accidental zaps from 72v; 12v is much safer. Just keep your wires short as you can to reduce losses.

12v, 132ah, you're looking at about 1.5kwh of storage. Phones, speakers, ect, are great, but those are going to be using like 5-10w each. Not much. If you're going to go through the trouble of setting up a mini solar system in your house, consider getting the full use out of it. I have my mini system powering one full room of my house, direct dc, no inverter: room lights, all USB charging, router, modem, tablet, computer, speakers, in addition to charging my motorcycle. It's lovely.

Thanks for the reply! My 100w solar panel has a 8.5A charge controller & according to the specs, it'll produce up to 100 W / 5.5 A of power under ideal conditions. I do have a brand new 760w Schumacher inverter that is just collecting dust, so I was thinking of connecting that as well & use it in the garage to also charge cordless tool batteries.

 

[dragon]

So looking through my parts shelves, came across some unused car audio stuff so decided to use it for this. Just need to put some finishing touches on the battery bank. The usb charger & the power inverter have their own power switch but should I hook up a circuit breaker to use as a master on/off switch?

 

[harrisonpatm]

Hey, that came together fast. Nice and tidy.

What's your main + and - for the battery? Is it that gray connector I see?

What port are you using for charging the pack? Will you be able to connect the solar panel, inverter, USB and an extra port at the same time? You may want to, maybe not. For example, I don't know where your setup is located, you may not be physically able to run a cable long enough to wherever your solar panel is.

If that's the case, then it may not be fully necessary to have an on/off switch. Like, if the gray connector is plugged into the inverter, then you have to unplug it to plug in the solar panel to charge... then you don't really need an on/off for the battery's main + and -, because the connector is doing that job.

If you still want an on/off switch, I'd recommend putting one of these on the positive line. Cheaper than breakers, and designed to be flipped on and off semi regularly, which breakers aren't. Instead of a breaker, consider a fuse for each device you add. For example, you said your inverter is 760w. At 12v, you can expect it to pull something like 850ish amps (efficiency losses), so make sure the cabling from the battery to the inverter is good for 80ish amps, and maybe put an 80amp fuse on that line as well, to not damage the inverter in case of overamperage. I see the inline fuse that you used for the USB converter; do you have a fuse on the inverter?

I really like your repurpose of several parts that you clearly had lying around and wanting to be use. My favorite thing.

 

[dragon]

Hey, that came together fast. Nice and tidy.

What's your main + and - for the battery? Is it that gray connector I see?

What port are you using for charging the pack? Will you be able to connect the solar panel, inverter, USB and an extra port at the same time? You may want to, maybe not. For example, I don't know where your setup is located, you may not be physically able to run a cable long enough to wherever your solar panel is.

If that's the case, then it may not be fully necessary to have an on/off switch. Like, if the gray connector is plugged into the inverter, then you have to unplug it to plug in the solar panel to charge... then you don't really need an on/off for the battery's main + and -, because the connector is doing that job.

If you still want an on/off switch, I'd recommend putting one of these on the positive line. Cheaper than breakers, and designed to be flipped on and off semi regularly, which breakers aren't. Instead of a breaker, consider a fuse for each device you add. For example, you said your inverter is 760w. At 12v, you can expect it to pull something like 850ish amps (efficiency losses), so make sure the cabling from the battery to the inverter is good for 80ish amps, and maybe put an 80amp fuse on that line as well, to not damage the inverter in case of overamperage. I see the inline fuse that you used for the USB converter; do you have a fuse on the inverter?

I really like your repurpose of several parts that you clearly had lying around and wanting to be use. My favorite thing.

Thanks!

The gray connector is an Anderson connector. I used that just because that was what I had readily available on hand. I'll use an adapter to connect to the sae wire that my solar panel has. The battery pack will prob stay in the garage. The box is kinda flimsy so I may use some scrap wood to beef up the bottom platform & maybe mount some casters to make it easier to maneuver around my crowded garage. My solar panel isn't mounted. I plan to just prop it up on the driveway & plug into the battery box when needed.

I used 4g (actually looks more like 6g) wire I harvested from some car booster cables) for the parallel wiring & the 2 main lines (1 positive line into the fused distribution box & 1 negative line into the small distribution box. I used scrap 8g car audio wires to run from the distribution blocks to the outside of the box, 1 set into the inverter & the other set into the gray Anderson connector. I have a 80a fuse on the inverter & a 40a fuse on the Anderson connector line. (again those were the fuses I had on hand haha) The cigarette plug on the left has a 15a inline fuse & the usb charger on the right has an inline 10a fuse & those are wired directly to the batteries for now.

I think for my own extra peace of mind, I will add a master shutoff switch.

 

[dragon]

Battery cut-off switch arrived so installed that & rewired the cigarette adapter & usb charger to the master switch.


Cut up my old DIY wooden bucket dolly & strapped the battery box to it so it’s easier to maneuver around the crowded garage. Added a little front lip so the extra cords & cables can be stored on the dolly too.


Just in time for Earth Day haha!