Sanity check of proposed battery solution

[powerlord]

Hi guys,

been tinking with electric bikes now for a few years.

Currently working on a battery pack and charger solution for my 500w 48v mountain bike conversion.

What I've got is 4 x 5500 RCKING 22.2v 6s lipos.

I have them rigged up in 2S2P for 11ah at 44.4v.

However at present I need to disconnect em all, remove from bike charge them 1 by one, etc etc... right pain.

So, I bought a GTpower Xdrive6 4 way charger which allows charging 4 6s packs in parallel (each at 6amps) which will allow me to recharge the whole pack quickly and safely with fully balanced charging.

However I'd like to get a bit smarter than that and avoid having to take pack to bits, etc to plug it all into charger.

So here is the plan:

- one dyecast aluminium box big enough for batteries,
- latching push switch and 2 x 24 pin PC PSU style connectors (male and female x2)
- 3 12v relays (which I'll switch on 22v) which can handle 30 amps.

I wire up each 7 pin balance lead + main power leads to female PSU connectors. 9 x4 = 36 pins in all.

I wire make connectors to my GTPower.

OK, so now the tricky bit - obviously before I actually charge I have to isolate each battery again - I can't charge then while they are still in 2S2P - so I need to break 3 connections:

- on each parallel pair, I need to break the +ve link
- i need to break the single serial link across the 2 parallel pairs.

hence - 3 relays (or one 3 pole relay- but I couldn't find one that could handle 30amps (my max load when in use), so I'm sticking with 3 30amps relays.

I control the activation of the relays with a flat mount push to latch button (cannot be pressed by accident), and use power from one of the lipo packs (22.2v) to switch them (rated at 12v but they should be fine at 24v).

So once all rigged up in the box. To charge all I need to do is either on or off bike, push charging button down, then connect charger 2 plugs to box (carefully marked A AND B so do not mix them up), and start charging.

Once all packs fully balance charged, removed cables, push button to open close relays (i.e. relays connected to close latch with no power) and away we go.

Does that sound like it'll all work fine or have I missed something terribly obvious ?

stu

 

[wesnewell]

For me, the obvious solution would be to buy a Hyperion 1420i charger that will charge up to 14s at 20A and never have to split the packs.

 

[powerlord]

your right of course, a 12s+ charger would have been nice, but difficult to find them in the UK.

so I've already got the GTpower, so making do with what I have.

at 6a x4 it will charge just as quick (or quicker) than the hyperion.

If I was going to use it every day, I'd be more inclined to search one out and go for your suggestion, but as it's just my 3rd leccy bike after the main commuter and folder, it is only going to get weekend offroad use.

Plus the 4 way lets me charge all my quadcopter batteries at the same time

 

[dogman dan]

Hmm deja vu. We just had a thread a few days back with the same problem.

Like last time, the same suggestions. First off, you shouldn't need to balance them daily. A well matched set of packs, you might not need much balancing monthly. If you are getting out of balance every ride, which I define as between .05 an .1v off, you might want to retire the pack that has a cell that won't stay within .1v of the others.

Once you do that, the problem just becomes one of building a wiring harness that with one plug, will make the transition from 2p to 1p. Too bad you already have the charger, but it is a 200w charger, so thats a decent rate of charging at least.

Icecube 57 showed us how, and sell harnesses if you want to buy one from him. The idea is basicly this. You have a three piece wiring harness. One piece attatches to all four batteies. With anderson powerpoles, it terminates in one big block for a single plug. Each section of the plug is a pair of andersons connected to one battery.

The other two sections are as follows. One section for charging, remains 1p. So that stays attached to the charger, and by plugging in the one big block, you are ready to go to charge all four packs, using the non balancing charge cycle of the charger.

The last wiring harness stays on the bike. It plugs into the same block of plugs as the charger plug, but then has the connections built in to have 12s 2p 44v 10 ah come out the other end. So it's first two Y connectors to get to 2p, p then the series connetion to get to 12s.

It will take quite a few anderson power pole connectors, and some wire to make it, but once done it's one plug from charge to run. Very simple and convenient once in use.

 

[powerlord]

hmm. thats actually a bloody good idea - externalise the harnesses.

The drawbacks are:

- big harness on bike
- needs high amp connectors as full currents going through (hence need for andersons)
-plug will be a fair size with 8 andersons.
- no balanced charging without disassembly.

however its clearly a far more elegant solution, has no moving parts, and less chance of you trying to charge with wrong things connected.

I like it. I'm in UK, so will need to make my own harnesses up.

I can use the pc psu connectors I've already bought as an all-in one balance outlet so I can balance occasionally without dissassembly too.

thanks!

sometimes the obvious thing is staring you in the face!

stu

 

[dogman dan]

The plug gets a lot smaller, just 4 andersond pp's for a setup to charge with a one port charger. The plug is only big to seperate 2p packs.

Maybe sell off your 4 port, and get a 200w 8s charger?

 

[powerlord]

One more question:

I connect low voltage monitors the the balance leads of the batteries when in use.

Do you reckon I could leave these connected when balance charging ?

i.e. assuming I add my big all in one socket to allow occasional balance charging - could I have my low voltage monitors all permanently wired into the same wires ?

I'm thinking yes, it should be ok - since they are voltage monitoring they will have very high internal resistance and shouldn't affect the chargers ability to monitor and discharge cells during the balance charge cycle. But be interested to know if anyone has done it.

 

[dogman dan]

Yes, you could have y connectors on the balance plugs, allowing the monitoring device to be on one end, then the other end could be your balance cable.

I don't recomend parking the bike overnight with ANY device plugged into it myself. If you park it with the devices plugged in, better be sure you always recharge it so you don't come back two days later to find the tiny device has drained the last wh from the nearly drained pack.

 

[o00scorpion00o]

I use 30amp andersons to connect all my bricks, and I have a 30 amp one for the controller end too and have no issues pulling 80 amps and 120 peak. Granted pulling 80 amps is during acceleration and not constant.

You don't need big connectors to series connect or to parallel the two packs as the current is split.

 

[powerlord]

Yes, you could have y connectors on the balance plugs, allowing the monitoring device to be on one end, then the other end could be your balance cable.

I don't recomend parking the bike overnight with ANY device plugged into it myself. If you park it with the devices plugged in, better be sure you always recharge it so you don't come back two days later to find the tiny device has drained the last wh from the nearly drained pack.

they use a few milliamps. I leave em connected for weeks and you'll get only a tiny amount of battery drain. So even if it was near the limit of flatness, it would only drain it by a tiny amount more after several days.

On one of my other packs, I have a gtpower watt meter permanently glued into the pack (water bottle type) - on 24/7. I can leave it for a month and it's only drained a tiny amount.

So no probs leaving them on all the time imho - saves forgetting to stick em on, etc.

You don't need big connectors to series connect or to parallel the two packs as the current is split.

well, the serial connection does not have the current split - it's the whole lot going through there.

But yeh I bought a bunch of 30amp ones.