using stripboards to parallel packs

[auraslip]

So... How many of you have been in the position of just having ordered a kwh or two of those 4s packs, only to research putting them in parallel for monitoring and balancing to find that their is no easy way to do it?

Like 20s would take 5 parallel harnesses from progressive and run you $50!

Or you can make your own harnesses, which would be cheap, but for 20s would require rigging up 50 connections per 5ah group.

Ok... that's super lame.



But look at that... it's only $0.02 per hearder http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=455-2242-ND

And it solders right to a board. And stripboards can be had cheap. Like a single $5 board can be broken up to do a your whole pack.

 

[auraslip]

Here is my basic idea. The labels are talking about contact sex and not housing sex.

I wanted to use the sideways headers so they could stick out the side of the board and the whole thing could be heat shrinked to protect against shorts, but that wouldn't work.

How can I protect against shorts now? Cover the bottom with tape?

 

[auraslip]

This thread on the rc site is very helpful! http://www.rcgroups.com/forums/showthread.php?t=932319



Bottom one looks like the real deal!

 

[auraslip]

So... I was pricing custom made PCBs.... and I could totally have boards made to make putting 4s packs in parallel easy as cake. And they'd be cheap too. Like 1/4 the price of buying the parallel harnesses.

Boards would be modular. From 4s up to 24s. Up to 6 packs in parallel. I would drop the headers and harness in myself. So everything would be ready to go! Anyone interested?

 

[neptronix]

Hm. What would be the cost of these boards?
I like this idea.

 

[auraslip]

I think it might cost me $10-$15 for the boards (24s4p) + $2-$3 for wiring and connectors + my time and shipping. Don't know. I've never designed a circuit board, but damn if it really should be anything different than the stripboards really.

I'm also thinking that they could be paired in 8s groups with 2x 4s outputs and one 8s output for cell logs. This way you can monitor with cell logs, and balance with the battery medics.

 

[adrian_sm]

Remember CellLogs are upto 8s, but Battery Medics are only upto 6s.

As for waterproofing, bit hard since the JST connections are not waterproof. But an electrical conformal coating or "Liquid Electric Tape" might do the job for the board. But if you are getting boards made, you can get them coated by the manufacturer.

- Adrian

 

[John in CR]

My plan is to get rid of the hard cases, so I can put the cells under better compression anyway, and then parallel with nice thick wire at the cell level leaving me just one balance tap. My thought is that will also be better for the cells, since weaker ones get help from their parallel buddies at all times.

My only concern about your way is what happens if a pack is out of whack? Wouldn't plugging it in parallel with other packs open up the potential for currents higher than those balance tap wires can handle?

 

[AussieJester]

Way to go.. using kilometers of wiring in harnessess
is the noob way IMHO... Add in some bus bars for the main
leads and your set, e.g-->

Once you have all the boards made up, grab yourself a few DB25 connectors to hook up your paralleled leads-->

Makes for a hassle free setup, no plugging and unplugging for charge and discharging and you get to
balance your packs all in one hit!

best of luck

KiM

 

[auraslip]

John - ohms law to find current through balance taps is the difference in voltage divided by the circuit resistance.

(4.2v-4v) / .05 ohms (assume 2 packs) = 4a
The connectors are rated at 3a so if you were to do something stupid like plug in VERY unbalanced packs, it could cause an issue, but even then the current would quickly equalize.
A better way to do it is to put them in parallel through the main leads first, check voltages, and then parallel balance taps. But it shouldn't ever really be an issue.

I also plan to remove them from the cases. Those damn cases make them the size of 6s packs almost! I was thinking of wrapping them in fiberglass insulation to keep them warm, provide cushion, and act as a very mild fire retardant.


AJ - we're talking about balance connectors. Those bus bars are freaking rad though man. I wish I covered that when I did your bike. I'm just going to solder the leads to ANL fuses, so each parallel group gets a low voltage fuse. After I'm sure the packs are working well, I'm hoping to only access them from outside the battery box for periodic balancing. Cell-logs are permantly installed on the bike and activated via relay that comes on with the main keyswitch.

Adrian - good call on the liquid electrical tape. That should prevent shorts on the stripboards. Really, the stripboards should be almost identical to the PCB. The PCB would just be nicer looking and have a isolation coating.

What might also work is to use the side entry headers in the first post. If I can solder two into the same space on the stripboards on the opposite side, then I could get four of them, run the balance tap from the middle, and then heat shrink it so only the headers are sticking out.

 

[auraslip]

Actually it looks the side headers are long enough to work as said in the last post. That's good news.

 

[AussieJester]

AJ - we're talking about balance connectors.

Look at the picture again, they ARE balance connectors that's why i posted them not
for the bus bars, the DB25 connector is used to connect to ALL the leads from the
two parallel adapter boards, the boards are exactly what your wanting to do they are made from the
strip board.

KiM

 

[dogman dan]

Assuming 20-30 amps max, Ep buddy has a paralell board with more beefed up traces. But that's a bit of the too much wire deal.

But really, I don't get the need to paralell the packs at the balance leads. A good cell doesn't need it and a bad cell needs to be bye bye. As you identify a weak cell, you can still connect to that cell through the balance jst to single cell charge it for awhile before you chuck that pack.

For the paralelling packs, cut the wires about 3 inches long, and connect just one wire with connector to that. Then make your series connection. If you are only paralelling pairs of packs, this works great. What too much wire? not one inch more than they came with. I could see this working ok even with up to 4 packs paralelled.

 

[icecube57]

Epbuddy has a 2 to 1 and a 6 to 1 and if you butcher a 6 to 1 and make a cutom harnes you could do that also... I think it come out cheaper than manufacturing the boards. Whats a little extra balance wire between friends This thread also makes me want to throw the reminder out there that you better know all your packs are good cause one bad seed will spoil the bunch when paralleling.. I like Aussie board. I like his whole pack system. Personally I had 3s 3p packs and I had 3 to 1 parallel balance taps I made that permenantly stayed on each parallel cell group and when it came to charging them I had another 3 to 1 balance tap to conenct the three sub groups together to make one large pack. It beats individually plugging a harness to 9 packs. My packs stayed very balanced. But then again i used to leave em on the meanwell with a battery medic for hours on end... Not cause they needed balancing but because I was lazy to take them off.. The paraboards from epbuddy are great also but I think it just leaves more room for you to frock something up if you had to disconnect every single pack from your harness to plug into the board and then plug the balance taps into it also. if you were using a whole board thats 6 pack disconnects then 6 pack connections to the board to the the board and then 6 more connections to plug in JST connectors... Thats why I like my 1 plug for discharge and 1 plug for parallel charging.. makes it easier to parallel the packs but you still have to fudge with the JST balance plugs.. Another trend I see is people dont want to dedicate to one voltage so it makes it to where they can create dedicated sub groups like I did. The want to run 44v 10AH one day and 66v 15AH the next ....But if i do see someone that is going to have a fixed pack voltage I do set them up with a system to where the parallel sub sections are permenantly connected at the cell level

 

[Andes]

This is exactly what I built for my A123 packs, here is a pic where you can see the boards. It is very useful, and very simple to use.

 

[auraslip]

I guess you guys haven't seen my latest build thread, so you don't understand what I'm going for:

Batteries are semi-permanently connected. All charging done using server power supplies/meanwell or on board bulk charger. All balancing done with battery medics.
This means the balance taps need to be in parallel and accessible from the water proof box. And it means I need to stick with these crappy jst-xh instead of something nicer like db25 to interface with the cell-logs.
Not worried about bad cells. That's why I ordered more than I need and built a discharge tester. If it happens over time it should show up on the cell logs.

I've seen epbuddies harnesses. They make some sense for 6s packs, but I'm not spending $50 for 5x 4s taps. And as AJ said, It would be a ton of wires. BTW, if I had the PCBs made they would be for 24s, but made to break off in 8s groups. So you'd only have to buy what you need.