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Parallel LiPo - charging & operation


#1

This is primarily to document how you can connect LiPo batteries in parallel.

The reasons why you might want to connect them in parallel are:

  1. To save time charging. You can charge all the batteries together with one charger at the same time.
  2. Reduced current draw from each battery (particularly during high power operation) will extend the battery life.
  3. The parallel pack will last longer during an activation than using the packs seperately
  4. Individual cell weakness is less pronounced.

Note that before you connect LiPo batteries together in this way, they need to be charged to the same voltage and obviously need to have the same cell count.

First of all you need to connect the main supply cables together, this is an adapter that I use:

The plugs and sockets are called Deans T connectors and you can find them easily on ebay.

e.g. http://cgi.ebay.co.uk/Deans-T-Plug-connector-x4-Pairs-High-current-/220636331370?cmd=ViewItem&pt=UK_ToysGames_RadioControlled_JN&hash=item335ef33d6a

I chose not to include any polarity or current protection, you might want to add fuses or diodes.

Next you connect the balance ports together.

This greatly improves the battery pack operation during high current draw and helps compensate for any weaker cells.

The connectors are called JST-XH and again you can get them from ebay.

e.g. http://cgi.ebay.co.uk/JST-XH-Balance-connector-set-4-cell-14-8v-/320498001228?cmd=ViewItem&pt=UK_ToysGames_RadioControlled_JN&hash=item4a9f2b654c

You need to buy the connectors with the correct number of pins for your batteries.
4 cell 14.8v batteries need 5 pin connectors
3 cell 11.1v batteries need 4 pin connectors

The following is an adapter made up on a small section of veroboard (copper strip board).


I have deliberately beefed up the tracks with lots of solder.

Before you connect your batteries together in this way, check that your balance ports are all wired the same with a volt meter.

Again I have chosen not to include any protection. You could break the tracks between the balance connectors and link them with fuse wire.

The final part is to make up a small balance extension lead. You can use this to connect a LiPo monitoring device or to connect the parallel batteries to the balance port on your charger.

Keep the lead short or it might pickup RF.

and finally this photo shows three different 5000mah packs in parallel powering an ft857d.

Hopefully the above will be of use to someone.

Regards,
Nigel. G6SFP.


#2

In reply to G6SFP:
Hi Nigel … your hope comes true HI
interesting info about LiPo’s I’m a fairly new user of LiPo’s and your information was very instructive, looked at your pictures (drooled on your car … sorry) and saw the one with the Shottky diode, I’m a bit confused, because you talked about connecting the JST-SH’s from 2 LiPo’s together …
love to learn more …

Regards
Patrick PD2PC


#3

In reply to PD2PC and G6SFP:

…looked at your pictures (drooled on your car … sorry)

Patrick,

I used to work in Blackpool in the 1970’s where they were made and they were quite common in the area. Great eye-candy of the mechanical kind.

Nigel,

An excellent post backed up by some brilliant photos. Those are humungus packs - they make my 4400mAH + NiMH approach to powering the 857 look positively puny!

73, Gerald


#4

In reply to PD2PC:

You would not really want to use the shottky diode if your going to connect the balance connectors together. Using the Shottky diodes is a safer way of connecting the packs together, as you can connect two packs with different charge levels (different voltages) and the diodes will stop any current flow between the two. I no longer use the shottky diodes, but I am very careful when connecting the packs together.

Connecting the JST balance connectors together effectively connects each individual cell in a pack parallel to the cells in other packs. This helps balance the capacity variations in individual cells and in my experience produces a better overall result.

Nigel.