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4s6p battery holder


(Etienne Demers) #1

Hello Guys,

I’ve been trying to solve the battery shipping issue for some of my international sales and I came up with the following solution.

The idea is you buy the battery holder and then you buy 18650 batteries locally.

You then just slide the batteries in and screw the holder shut.

Just testing the water to see if anyone would be interested.

First model would not have a BMS.

Cheers,
E.


(Drew Fulton) #2

That is a really intriguing idea. I don’t care as much about shipping but I travel with the ROV for work and flying with batteries is an issue. Can’t fly with the BR batteries and even using smaller LiPos, I’m usually limited to 2 batteries due to limits on 150wh batteries. Be nice to travel with a large number of 18650 cells which they would allow, and a couple of these holders and then assemble on site.


(Luc) #3

@etienne
That’s a nice idea i had some times ago, but with 3D printer parts as battery holder.

Since the goal is to build a rather powerful battery the hard part of the design is the quality of the electrical contacts.
If a single of them is bad, it’s going to overheat.
And then :

  • unbalance the current between cells, which in turn could damage them
  • overheat a cell, damaging it or worst, firing it !
  • overheat the PCB, with similar result

I already realised this kind of pack with spring loaded contacts, but since the power was low, there was no problems.
For example :

I temporarily gave up this project because i had no time to experiment, but i’m still interested, let me know if you go further !


(Etienne Demers) #4

Hi Luc,

This is very nice indeed. I wish there was more space so I could print a nice bracket like this but the idea is to keep the same battery format.

First prototype will be using some battery springs. I think this will ensure better contact. The alternative would be to machine copper buttons but I am afraid this might not be making as good contact…

If this works out I will use the underside of the board to make a BMS and find a place to stick a few temperature probes and shut off circuit…

Cheers,
E.


(Luc) #5

Hi Etienne,
spring loaded contacts are the first choice, but it’s very hard to find their electrical specifications.
In this case, in my opinion, the contact resistance should be lower than 5 milliohms.
Even with this low value, dissipated power in a single contact is 0,5W for 10A per cells string ( 60A for the whole battery ).
This give : 24cells x 2contacts x0.5w = 24w dissipated just for contacts ( and probably as much in the PCB )
Perhaps this type of contacts will fit better ?


(Etienne Demers) #6

I like it.

Do you have a link so I can check it out?

Cheers,
E.


(Luc) #7

Here is it :
https://www.cotelec.fr/media/springloadedcontactscotelec2011__097150800_1138_06052011.pdf


(Etienne Demers) #8

Thanks I will look into it.


#9

I love it! The standard battery setup is a little annoying. You can’t put the battery in leads first because there’s no room for the connector to sit along the side and packing the wires and connector in the end kind of wants to push out the end cap. Having the battery connector fixed and in turned 90 degrees should allow you to shorten the leads so it all fits in there perfectly.


(Etienne Demers) #10

Ok taking everyone’s comments in consideration I changed my design a bit.

Its a bit on the long side due to the pogo pins but it should still fit the 3inch Plexiglas enclosure.

Putting this into production now. Hopefully will bet it ready to roll soon.


#11

Sorry I wasn’t clear, I actually like how you had the connector before. When they’re straight like you had it before, there’s no bending of the wires. Also, the amount that the solder has wicked into the wire, depending on who put things together, doesn’t affect how it fits. Also, I’m new to BR world, so take it all with a grain of salt.


(Etienne Demers) #12

Hello Corndog,

I actually had to change the connector due to the pogo pins protruding the board and having to isolate them with the plastic ends.

I have to put it this way else the unit would be too long.

Lets see how it works out.

I am hoping to have the first unit ready in 2-3 weeks.

Cheers,
E.


#13

Sounds good. I’m definitely interested in a kit. Have you been able to put a price together?

Also, how difficult would it be to add balance leads? I know you could take it apart and balance them with a charger that takes individual cells, but it might be a nice option.

For what it’s worth, I don’t have any interest in a BMS.


(Etienne Demers) #14

A balance lead will be available with fork connectors. I just didn’t bother to draw it :slight_smile:

I’ll update you all on the cost once I know my build cost.


(Etienne Demers) #15

So I got a quotation for 5USD per pin and I need 50. Counting the other parts, the assembly, inward shipping costs. I would have to charge 800USD per battery holder.

Ykes!!!

I think I should try for spring instead :slight_smile:

I was hoping for the selling price to be max 400USD…


#16

Have you seen the solderless setups for DIY e-bikes and whatnot? You may be able to incorporate some of that hardware into your design.

https://vruzend.com/


(Etienne Demers) #17

Thank you for the suggestion but it does not address the contact issue for 30A discharge. Also, as you know space is very limited in the enclosure.


#18

Plenty of e-Bike stuff pulls 30A+ and the kickstarter info says as high as 20A per cell, so it should be okay in that regard, but really I just mean that maybe there’s a similar method of assembly with a fastener through a piece of copper bent over itself for the spring contact. The only “hard” part would be the dimple and the only extra space it would take is above/below the cell, which is where there’s some extra room. It’s less of a plug & play solution, but maybe something to think about if there isn’t an off-the-shelf product that fits your needs.


(Scott W) #19

Etienne

I had been looking at something quite similar (but based around some 3" schedule 80 pipe to get depth ratings of around 1km)

I was going to drop the 4S6P down to 4S5P and give up some power and duration for the sake of being able to have the unit travel by air with removable changeable batteries

Due to the equipment I have easy access to it was basically 3 off 25mm thick hockey pucks of machined delrin where the top and bottom pucks were bored out to about 15mm depth

The intention was to use the 5222 battery holder https://www.digikey.com.au/product-detail/en/keystone-electronics/5222/36-5222-ND/2745881 which fit internal to the 18mm of the 15mm countersunk battery hole

This could also be done via 3D printing (similar to @luc-rossi work)

Scott’s Batteries.pdf (3.0 KB)


(Etienne Demers) #20

I haven’t given up on the pogo pins yet. I am negotiating with the suppliers.

The springs I put on my original design are 211-D also from digikey.

I asked the manufacturer for current ratings. Lets see if they respond. What is nice about those is they mount with pop rivets.