First build, commuter from scratch - advice appreciated!

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d8veh   100 GW

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Re: First build, commuter from scratch - advice appreciated!

Post by d8veh » Dec 14 2014 6:44am

The problem with used laptop cells is that you need to test them individually for capacity before using them, which takes a long time. Often, they're worn out, which means that they charge up to 4.2v OK, but they have massive sag and go down very quickly. You only need one cell- group with bad cells in to ruin the performance of the battery. My advice is to make up a 6S jig and do a discharge test on every cell with a r/c charger like an Imax.

Also, the older type cells are relatively low on capacity for their weight compared with modern ones.

Having said all that, you can still make a useable battery out of recycled laptop cells if you have a supply of good ones and/or take your tome checking them.

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dogman dan   100 GW

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Re: First build, commuter from scratch - advice appreciated!

Post by dogman dan » Dec 14 2014 7:04am

Once sorted, the general rule is to build a huge pack, so the laptop cells are not subject to very high c rates. So go big, 20-30 ah of it.

Cephalotus   10 kW

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Re: First build, commuter from scratch - advice appreciated!

Post by Cephalotus » Dec 14 2014 10:40am

Good 18650 cells start under 3€ over here: http://eu.nkon.nl/rechargeable/18650-size.html (this is incl VAT)

I wouldn't built a e-bike battery from old notebook cells, even if I could get them for free. I wouldn't do it even if someone would pay me jzst to use the cells.

It's not worth all your precious time for testing, selecting and making such a pack that will behave much worse than a pack from new high quality cells suitable to do the job and with high possibility you will spnd the next hours for testing and repairing after just some day of use. Cells will fail frequently.

Ok, if your hobby is soldering instead of riding, it could be an option.

RTFH   100 µW

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Re: First build, commuter from scratch - advice appreciated!

Post by RTFH » Dec 14 2014 2:39pm

Hey, OP here. Looks like my account's been deleted, I'm guessing because my post gave the impression I hadn't read up first? I'll make a more succinct post only asking what I really haven't been able to find.

Anyway thanks for the replies. I believe the cells are fairly high quality (got em from someone who's built bikes out of same stock), so I'll just test thoroughly and try my luck.

RTFH   100 µW

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52v with 48v controller and charger?

Post by RTFH » Dec 14 2014 3:00pm

Hi all,

Quick question I haven't been able to find the info for,

I have a 48 volt 1500w controller and a 48v charger and am building a pack out of 18650s. I was going to build 13s (48.1v) pack and bms but am tempted to go for 14s (51.8 ) for a little more power.

Would that fry the controller? Would the charger only chg to significantly below capacity?

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biohazardman   100 kW

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Re: 52v with 48v controller and charger?

Post by biohazardman » Dec 14 2014 4:58pm

Check the maximum voltage on your charger expect it is at least 52-58V and made for 14-15s as most rate their Lifepo4 battery packs by their nominal 3.3V resting voltage and not their full charge rate voltage. So chargers are set to output higher than the specified voltage for the pack. The two 48V chargers I just checked say the output is 58V constant so higher than the maximum of 3.65 for 15S I us use for a cells maximum voltage. As for the controller if it's for 48V it should be good for 15S. So, you are aware 18650 cells need to be in a 4p to 6P configuration depending on the maker and individual cell as well as your series connections or you will toast them?
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Simple818   100 W

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Re: 52v with 48v controller and charger?

Post by Simple818 » Dec 14 2014 6:11pm

Your charger will have to output 58.8 volts and your controller should be fine cause it most likely can take 60 volts.

RTFH   100 µW

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Re: First build, commuter from scratch - advice appreciated!

Post by RTFH » Dec 14 2014 9:49pm

@biohazardman the cells are not lifepo4, so nominal is 3.7v. Do you still think controller can take 14s? Also I hadn't heard about parallel restrictions (aside from reasonable c rate), is that just lifepo4 or all? I'd heard that with laptop 18650s more p the better, my in frame pack is 9p and I'm planning on building a lond distance pack to tie into it adding 12p (21p total).

@simple818 hope so bout the controller, it was cheap so I'll just go for it.

Thanks all for the info!

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dogman dan   100 GW

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Re: First build, commuter from scratch - advice appreciated!

Post by dogman dan » Dec 15 2014 6:20am

63v is usually the absolute maximum for 48v controllers. So no problem with 14s that charges to 4.2v.

d8veh   100 GW

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Re: First build, commuter from scratch - advice appreciated!

Post by d8veh » Dec 15 2014 12:33pm

Many of the aluminium-cased chargers have a voltage adjuster pot inside, so you can turn it up to 58.8v. There's no point in adding an extra cell-group unless you change your charger. If your charger is already 58v (for 48v LiFePO4), it would be better for 14S because that's too high for 13S.

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