Converting EV Global Motors SX 36v to LiPo

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docrocket
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Converting EV Global Motors SX 36v to LiPo

Post by docrocket » Apr 12, 2018 6:08 pm

Hi! Occasional e-biker, occasional reader, first-time poster. My technical expertise is at the level of "I believe it runs on some form of electricity" and I know the difference between a watt and an amp, but past that point, as a bike tech I'm about capable of adjusting a derailleur. Barely. So please be merciful.

I have an old EV Global Motors SX 36v, the classic Iacocca bike, with SLA which still runs great and which I use for my daily 15-mile round trip commute. It works, barely, for that; I ride it in, charge it, ride it home, repeat. I usually arrive at work with a fluttering erg or two left in the tank but no more. The battery pack is older and undoubtedly at the end of its useful life. It needs to be replaced. My budget is very low.

I would like to convert the bike to LiPo. In fact, I have two 12v 8Ah LiPo battery packs and their charger from a different e-bike which I no longer have. I suspect that this would actually be cheaper than buying new SLAs, because my understanding is that I can keep the existing 500w motor (which still runs strong) and that all I actually need is a new controller, plus whatever mechanical modifications I need to jigger the new battery pack(s) into the old spaces. Looking at the frame, I can easily fit one of the LiPo packs into the oversized downtube on the bike, and swap out packs if I kill one during a ride.

1) Am I basically OK in my approach here, or am I wrong on some fundamental point?
2) What kind of controller do I need?
3) How hard is it to make the swap and rewire the innards?
4) How about the battery terminals? The SLA pack uses a different kind of connection to the bike than the LiPo packs have.

Thanks in advance for help and advice!

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wesnewell
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Re: Converting EV Global Motors SX 36v to LiPo

Post by wesnewell » Apr 13, 2018 1:08 am

You don't even need a new controller, assuming the one you have works. Just replace the sla batteries with a 10s lipo pack. Should easily fit where the sla 's are now. I'd assume you could even use the old charger although it will probably not give you full 42V charge.
Need Advice? https://endless-sphere.com/forums/viewt ... =3&t=66302
Mongoose 26" Ledge 2.1 mtb bike $99, yescomusa.com 48V 1000W rear hub kit $200, Hua Tong 72V 40A controller $35, 10ah 24s lipo $217=~43mph, range=45 miles @ 20mph. 25K miles and still going strong.
Huffy Fortress 3.0 with MXUS 3000 4T motor, 24s lipo, 96V 60A controller. Total cost with extras <$700. Top speed ~50mph
My videos https://www.youtube.com/channel/UC0KW4U ... _G2wQhptMg

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dogman dan
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Re: Converting EV Global Motors SX 36v to LiPo

Post by dogman dan » Apr 13, 2018 8:51 am

Yes, and replace your basic understanding enough to deal with lipo. Just basic stuff, like 10s lipo is 36v, how to solder on a plug that matches your lipos, understanding parallel and series connections, and the basic hazards of charging and storing lipo, or any other lithium battery for that matter.

I would not sweat too much on fitting it all in the old container. Just get some good thick wires coming out of it so you can connect up to a lipo carried on a rear rack. Lipo is light, so no problems with the weight of it there.

36v 10 ah would be ideal, but you already have some 8 ah packs, so maybe a 4s pack added would work great. I'm assuming you have 3s now, which is actually a bit light for 12v, but 4s is too heavy for some 12v stuff...

End up with at least 10s 8 ah.. then consider adding some more ah of 10s later. like build on another 5ah.

When you add lipo, it will become mandatory that you have some kind of on board voltmeter. You can't run them till dead like you did with the lead. You have to stop at 35v, when the power is off.

docrocket
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Re: Converting EV Global Motors SX 36v to LiPo

Post by docrocket » Apr 13, 2018 2:33 pm

Thank you for the help.

OK, now comes the part where I reveal my ignorance.

The packs I have (photo attached) I think have a battery management system in there already - the old e-bike would shut off when the pack was drained. But it sounds like I need to open these packs up and take the cells out, get a couple more individual cells, and wire them all together to get up to 10S / 36v.

Can I then use the voltmeter/BMS inside one of the packs on the new frankenpack?
Image

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wesnewell
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Re: Converting EV Global Motors SX 36v to LiPo

Post by wesnewell » Apr 14, 2018 2:21 pm

Battery packs made with 12V sla batteries don't use a bms. I't s just three 12V batteries wired in series that are charged with a 36V charger. If that pack has a volt meter on it, you can use it but will probably be hard to see when riding. I'd assume the the cutoff voltage for a 36V sla system will be 31-32V. A 36V sla pack usually charges to about 40V, while a 10s lipo packs full charge is at 42V. You really don't want to run a 10s lipo pack below 35V even though you can go as low as 30V on it according to most lipo specs. Anyway, inside your case you should see 3 12V batteries in series. just remove then and replace them with 2 5s lipo packs in series for 10s. You can put a 10s bms on it if you want to. Personally, I wouldn't bother, but technically you should for safety. I prefer to mange them myself when needed.Not really much to it. Just connect the positive and negative of the 10s pack to the same as the positive and negative wires the 36v pack was connected ]o and you're done. Check voltage and charge as needed. 10AH of 10s lipo should get you more than twice the range as the 36V sla pack and also more acceleration power and speed.
Ref:
http://scriptasylum.com/rc_speed/lipo.html
https://www.rchelicopterfun.com/rc-lipo-batteries.html
Need Advice? https://endless-sphere.com/forums/viewt ... =3&t=66302
Mongoose 26" Ledge 2.1 mtb bike $99, yescomusa.com 48V 1000W rear hub kit $200, Hua Tong 72V 40A controller $35, 10ah 24s lipo $217=~43mph, range=45 miles @ 20mph. 25K miles and still going strong.
Huffy Fortress 3.0 with MXUS 3000 4T motor, 24s lipo, 96V 60A controller. Total cost with extras <$700. Top speed ~50mph
My videos https://www.youtube.com/channel/UC0KW4U ... _G2wQhptMg

docrocket
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Re: Converting EV Global Motors SX 36v to LiPo

Post by docrocket » Apr 14, 2018 2:49 pm

The packs in the picture are LiPo.

markz
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Re: Converting EV Global Motors SX 36v to LiPo

Post by markz » Apr 14, 2018 4:31 pm

You need a Low Voltage Cutoff for LiPo whether thats in the controller or a Cycle Analyst.

docrocket
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Re: Converting EV Global Motors SX 36v to LiPo

Post by docrocket » Apr 18, 2018 9:19 pm

Ok, project update.

I actually have two 7S LiPo packs. The plan is now to combine them in serial to make a 48v pack and overvolt the bike.

Will the charger I have (meant for the 24v packs) charge the combined pack, or is it's lower voltage going to mean the pack only charges to 24v? I suspect the latter, and I will need a new charger.

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Re: Converting EV Global Motors SX 36v to LiPo

Post by wesnewell » Apr 19, 2018 8:24 am

Assuming the original controller was a 36V controller, you'll likely need a new 48V controller for a 14s lipo pack. As for charging, you'll probably want a new charger rated for a max 58.8V output for 14s lipo. Or, you could split the 14s back to 7s and charge them with a 24V charger as long as the max output of the charger does not exceed 29.4V.
Need Advice? https://endless-sphere.com/forums/viewt ... =3&t=66302
Mongoose 26" Ledge 2.1 mtb bike $99, yescomusa.com 48V 1000W rear hub kit $200, Hua Tong 72V 40A controller $35, 10ah 24s lipo $217=~43mph, range=45 miles @ 20mph. 25K miles and still going strong.
Huffy Fortress 3.0 with MXUS 3000 4T motor, 24s lipo, 96V 60A controller. Total cost with extras <$700. Top speed ~50mph
My videos https://www.youtube.com/channel/UC0KW4U ... _G2wQhptMg

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dogman dan
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Re: Converting EV Global Motors SX 36v to LiPo

Post by dogman dan » Apr 19, 2018 9:21 am

Yes, those sure aint EVG lead battery packs.

Once you put them in series, you will have 48v, which will quickly fry your Heinzmann motor. Even quicker it will fry the original controller.

Tear those apart, find out they are dead inside anyway, and then start over with something 36v.

docrocket
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Re: Converting EV Global Motors SX 36v to LiPo

Post by docrocket » Apr 19, 2018 11:47 am

They're not dead inside, they have a full charge.

I'm thinking that I'll wire them in parallel instead and make it a 24v 16ah pack and undervolt the motor instead. Same hardware across the board (my budget is close to zero) and top speed is not a big concern for me. This is a commute bike not a fun bike.

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