Series wired battery gone wrong?

medusa569

100 W
Joined
Sep 17, 2010
Messages
161
Location
Washington DC
Hey all. I have rewired my old Ezee battery ( one cell went "bad") I'm going to repack it in an old camera bag and remove the bms. I am assembling it together and thought all was well with the world...BUT... one pack measured 18.17 V and the other measured 20.24 volts. For series wiring that should have given me 38.41 volts but that 's not what my meter is getting. It 's reading 20.62.... I don't get it. The connections look right so have I missed something?

battery series.jpg
 
I see the two negative battery black wires joined together and the two battery positive red wires going to the output plug. Obvious incorrect for series connection of the two batteries.

major
 
I am seeing the same thing as Major. If you are exiting one half of your pack with a negative cable, you need to go to a positive terminal or you have an improper series.

:D
 
medusa569 said:
one pack measured 18.17 V and the other measured 290.24 volts.
I'm assuming that "290.24" volts is a a typo, and it's supposed to say 20.24. Otherwise something is probably wrong with your voltmeter. ;)

For series wiring that should have given me 38.41 volts but that 's not what my meter is getting. It 's reading 20.62.... I don't get it. The connections look right so have I missed something?
Unless my eyes are just getting lost following the curlicues of the wires, I'm seeing the same thing.

both negatives (black wires) are tied together at the batteries.

the positive of the lower righthand pack is at the red anderson via the fuse, and the positive of the upper lefthand pack is at the black anderson.


Wired like that, measuring across the andersons you should get only about 2v, the difference between 20 and 18. If you're reading anything else, then either something is wrong with your meter or your connections/wires.


To get them in series for a 10s battery, you have to wire the positive of one pack to the negative of the other. Then the negative of the first pack becomes the main negative, and the positive of the second pack becomes the main positive.

Once that's done, you also have to charge up each cell individually so they're all the same, before you bulk charge the pack, or some will end up undercharged and some overcharged. If you are going to put a BMS on there to do teh balancing and prevent that issue, it'll still make it easier on teh BMS if you do this.



If you want them in parallel, for a 5s battery, then you'd wire both negatives together as you have, and then both positives together. Then run your red anderson via the fuse to the postives, and the black to the negatives.

BUT: before you connect them in parallel, you should charge each pack to the same voltage so you don't get currents flowing from one to the ohter, which might exceed the charging current limits for the cells (especially if they're old). Best to charge each cell to the same voltage, but at least each pack.
 
Thanks to all who replied. Yes I had the jumper wire wrong. It's reading correctly now. I also want to eventually make a duplicate pack so I'll have the option of riding with 36 or 72 volts.....saddle bagging the packs as it were. I also thought of adding individual on/off switch into each harness. Can I add each switch next to the blade fuse on the red leg of the wires?

BTW can anyone identify what these types of cells are called. I've surfed and can't seem to find quite the same thing. The closest I've seen is something called prismatic cells. But I am not adverse to making the other pack from 18650 cells. I'll assume I have to match the amp hours and voltage to be the same...36 v 10AH.
 
If you want to series two packs, you need more than switches in series with them, or else all you're doing is disconnecting the entire set from the controller. If you have them in parallel, you dont' want to disconnect either one, but instead always have them in parallel, so the load is less harsh on each one, making each one last longer and deliver more.


If you really want to switch between series and parallel, you'd need to setup switches to first disconnect all of the pack ends from everything, then reconnect the pack ends in the other configuration. If this is not done with a single switch, then you MUST switch them in the right order or you will short them out and possibly cause a fire. (most likely at least damage wiring and cells and switches, even if you have no fire, unless the fuses manage to protect the wiring from the misconnection, and then you need new fuses).

Or, you have to put plugs on each pack for each end of the pack, so they can be disconnected from one and reconnected the other way. Since you have andersons, you can put the battery and connector plugs into a single block locked together, but not plugged into anything, and then make two different mating plug sets. One will connect the packs in aprallel to each other and the ocntoroller, then the other one will connect the packs in series with each other to the controlller. Since the blocks can't be plugged in at the same time, you can't accidetnally short anything.

You can also use this a sa safety key, unpluggin g this block when you leave the bike. IF the other andersons are securely affixed to each other so they cannot be unlocked from each other, then noe one can udno them and reconnect them to be able to ride away or to short things together accidentally (or on purpose), etc.



If you run 72v, your controller has to be rated for better than the full-charged voltage of that pack, or you'll blow up parts in it.

There are some contrllers that automatically switch between a range of voltages, but others will require you change an internal jumper when yo uchange battery voltage. Others will only work at one voltage, or sometimes two that are close (like 36/48). So you'd need to check yours can do this in a way you're willing to deal with.



It's also going to mean your wheel speed will be twice (unloaded) what it was with the 36v, so your throttle will basically have half the resolution it used to. A small amount of throttle that got you 5mph before now gets you 10, and what got you 10 now gets you 20, etc. Harder to control at lower speed amounts. Unless you have a power- or current-throttle based controller, or a CAv3 that is setup for those types of control vs the much more common speed-based control.
 
thanks Amberwolf. I am aware of the need for a broad capable controller and I've seen there are a couple that alleged to have this. Far off into the future I would ideally have 2 packs at 36 volt and would keep riding art 36 volt but just have longer distance capability. So that would mean that both packs would have to be wires in series also. With my current setup since my old ezee pack was basically 2 20volt packs wired together I would think that a parallel connection would not be possible since that only offers 20volt which is not enough to start any ebike controller. For the time being still trying to get my old system up and running again.
 
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