Harness help

[Howie]

3 posts lost, won't lose a 4th...

Adding another 20s for 20s2p. Can I run two 20s strings and then parallel them? I saw some mention of another way, but don't know the benefit of what seemed more complicated.

I have a 900W BMSBattery charger coming, will it see it as a 20s 16Ah battery?

Can I run a battery medic in balance mode on each balance tap to protect from a runt cell causing problems? I have 8 or 9 of them so it'd be cool to be able to use them.

I'll babble about being excited to try the ice tires some other time since if I lose this post, the laptop is going off the balcony, and then I'll never solve the mystery of the paralleled pack.

 

[rui_fujino]

20s2p setup is exactly the same as mine so you can take a look here:
http://endless-sphere.com/forums/viewtopic.php?f=3&t=29799&start=15
this thread show's the diagram of how you should be setting them up.

the reason why you want to parallel the batteries before seriesing them is due to keeping individual cells from going off balance.
by paralleling the batteries first, given that balance tabs are also paralleled they will balance each other nicely :wink:
so you will only need 4 battery madic to balance them while charging.

I would suggest you invest on slow balance charger as well cos it is important to balance perfectly once in a while because they can go off balance if you keep bulk charging them :wink:

 

[Philistine]

In answer to your question on AH, the BMS bulk charger doesn't care how many AH there are, it just sees voltage, so the fact that you have added a second string is irrelevant to the charger, it just means that it will take longer to charge the pack from flat (because there is double the AH). A bulk charger like that simply raises the voltage to its set level. Whilst it is good to have a balance charger to balance charge every now and then (although you would need to split the pack in two to charge like that), I personally think people get way too stressed and hung up on balancing lipo in my opinion. As long as you do a good job to begin with when building the pack in checking your packs, and carefully balancing them (and then even more so if you parrallel the balance wires), then as long as you don't go too deep on discharge, then I wouldn't worry about balance charging actively as long as you keep an eye on your cells. I have lipo packs that I have not balanced in a year since creating the pack (bulk charging everyday), and the cells have hardly moved out of balance.

 

[Ricky_nz]

I personally think people get way too stressed and hung up on balancing lipo in my opinion. As long as you do a good job to begin with when building the pack in checking your packs, and carefully balancing them

I agree, my pack I built in june after I checked and balanced the cells properly (self dischargde and capcity) is still within 10mV max cell difference through bulk charging only. I do however check regularly in case a cell starts to fail. If your cells fall out of balance in less time then you didn't check and select your cells used in the pack very well. This pack is discharges 70% every 2 days and recharged. It has had a few deep discharged down to 3.4V ish per cell

At the same time it only takes one cell to fail (of have high leakage) and your charging experience could be shall we crispy! so checking is important, not the balancing. Only balance if the error starts growing

 

[Howie]

Thanks for the replies, that diagram helps me understand how to set it up and it makes sense now. The balance plugs don't need to be messed with, except when charged, then they're paralleled if I understand correctly.

I do have a balance charger that can do up to 10s and I balance charge once in a while but everything stays nicely balanced, but I'll keep an eye on it. I ordered the 900 watt charger on 10/31 so I'm looking forward to that. It'll be nice to just hook up once and charge the whole pack instead of always breaking everything down.

I can't find anyone that has the jst parallel harnesses for the balance taps right now so I guess I can work on the main connectors while I wait on the batteries. I think while I have everything apart I may put a switch on the precharge circuit. I have bullet connectors on it now that I plug together, wait a second, then make the main connection, then unplug the precharge. The switch would be nice, but would there be any problem if I forgot and left the precharge circuit closed?

 

[GMUseless]

Howie, update your location in your profile and we can help suggest vendors and products for you.

MethTek.com has everything you need for parallelling balance connectors including JST harnesses and parallel boards. If you want to take it a step further, he's got complete parallel boards with Low and High voltage cutoffs which is nice safety when bulk charging.

Many people leave the packs parallelled all the time, not just when charging. This helps to keep the cells balanced as a weaker cell can be helped by a stronger cell. Just be careful you don't series and parallel the entire pack at the same time. http://endless-sphere.com/w/index.php/Why_You_Can%27t_Connect_Your_Batteries_in_Parallel_and_Series_at_the_Same_Time

In packs that are evenly split for charging, I like to make up a mains harness with groups that can be seriesed or paralleled automatically depending on the mating connector. I run 12s6p on a couple of bikes. So I have two 6s6p groups. The harness from the pack is made up of four connectors (plus and minus for each pack.) The mating connector to the controller has four connectors as well...but tow of them have a jumper from one groups plus to the other groups minus. So when that's plugged in, two wires lead back to the controller as a 12s2p pack.

For charging, I have another connector that parallels the two groups together....then I get two wires headed to the charger as 6s12P (two parralell groups of 6s6p). In this configuration I leave each group's balance taps paralleled all the time, and never have to touch the balance taps. Each 6s6p group has a balance tap harness running out from the group. So to charge, I simply plug in the charge harness, plug each groups harness tap into the High and Low side balance connection on the charge (I'm using Hyperion 1420) and go.

No breaking the pack, no breaking the groups, no touching harnesses. Many people on ES have different approaches to this concept, but the key is to simplfy and minimize the number of connections you make on a routine basis. Even the most careful people will eventually make a mistake in the connections.

You should be able to come up with something similar with your setup.