Multiple Subpack Balancer

[retepsnikrep]

I've been thinking about this a lot recently as I am getting more and more enqs from members in UK about help with battery issues as the vehicle stock ages.

The Triton and Overloader Nimh Chargers are good but take ages, some times weeks and can really only do one or two sticks at a time, they also require a lot of user intervention changing over subpacks and noting results etc.

We need something much more automated that also does not require complete dissasembly of the battery.

We can't do it using the BCM balancing connector due to the low current allowed by the inline 180R resistors. We need access to the ends of the subpacks.

So my proposal is make up two end pieces using some light foam board and the orange connector boards as pattern for the holes to line up with the supack terminal bolts.

To this board fix neodynium magnetic connectors resting on some foam fubber to absorb any slight misalingment. Then we can just put these boards onto each side of the pack and have access to each subpack with a reasonable (5A) current connection and without dissasembling the pack.

So now we have 20 wires from each side of the pack this feeds to a pcb containing 40 x dpdt 5A relays. These relays allow the subpacks to be isolated and connected individualy to a 5A charger or 5A load respectively.

A pic monitors the cell voltages and current and the device can be programmed to discharge one cell whilst charging another. The pic logs the data and starts at subpack one and then advances through the pack with no user intervention simultaneously charging and discharging different subpacks, before finishing off with a quick top up charge of each subpack at the end of the cycle. It only needs a 5A 12v dc supply and can be left unattended with the device also controlling the pack fan so that can be activated if reqd for cooling. It would also be possible to use the bcm plug to access the ptc strip temp sensors and provide a warning of an individual cell overheat scenario.

It sounds complicated but it isnt really and can be left to get on with it, and can be changed to a new battery pack in seconds due to the magnetic connectors. (neodynium gold plated disc magnets about 7mm diameter) which fasten themselves to the subpacks bolt heads.

I'm working on a circuit diagram I'll post details later. I may well get a pcb made up if anyone is interested.

I also though about using a DC-DC converter as the load which would pump the discharging energy back into the charging side of the circuit so we are not wasting so much energy.

I think the circuit needs to be designed so it can be made easily and not use surplus parts that may be unobtainable next week.

[Hybrid-Battery-Repair]

Originally Posted by retepsnikrep

A pic monitors the cell voltages and current and the device can be programmed to discharge one cell whilst charging another.

Wouldn't you have interaction between the set being charged and the set being discharged?

Also, if you remove the end you can simultaneously recondition 10 pairs of sticks by using 10 chargers. (or maybe that's 9 pairs + 2 sticks)

What about modifying the end so that the sticks are not attached in series and then add a second, removeable plate over it that connects them in series? This way the PTC strips would stay connected.

[retepsnikrep]

Originally Posted by ogregev

Wouldn't you have interaction between the set being charged and the set being discharged?

Also, if you remove the end you can simultaneously recondition 10 pairs of sticks by using 10 chargers. (or maybe that's 9 pairs + 2 sticks)

What about modifying the end so that the sticks are not attached in series and then add a second, removeable plate over it that connects them in series? This way the PTC strips would stay connected.

They charge/discharge circuits are/can be electrically seperated by the relays.

You want to avoid taking the ends off IMHO. It's a right pain, time consuming and easy to damage the ptc ends especially if the process needs doing every couple of years to keep an old pack in shape.

I think it's best to do the sticks individually or you can't isolate a bad subpack without doing further work. This system will show up bad subpacks without extra work. I want it super simple to connect and operate.

Remove pack from car, take off the relay board, attach the magnetic connector boards and press the go button! Come back in a week with it all done for you and a nice text file for the pc detailing the data pack/performance.

I don't know about your experience but are there actually many bad subpacks (dead cells etc) or is it just they have gone out of balance.

In the two packs I have seen done, one had a bad subpack and the other was ok after rebalancing and a few decent cycles.

I've got a couple of spare packs which I can test all this on, and I can keep a rebalanced one in stock and swap them out for people in trouble and then do their pack at my leisure and pass that on to the next person.

[IamIan]

just my 2 bits.

Although it would only go down to a 12 cell or 2 sub-pack level... I would think it would be much easier for connecting and disconnecting to only attach to the plastic piece side and just leave the circuit side alone.... but single sub-packs level is nice, it just needs both sides to come off to connect.

Even at a ~5 Amps rate it would take over ~20 Hours just to charge the pack up once discharged... If you are going to spend ~20 Hours is would be much less complicated to just charge the whole 120 cell pack at once with one of the ~180V ~300mA trickle charge methods people are using.

For discharging it would still be useful to narrow down to one or two sub-packs at a time... if you do 1/2 the subpacks at one time skipping every other one in the series chain ... to avoid discharging interaction ... and then the other 1/2 second... you should be able to discharge the pack much faster , and just as safe... it would cost more... you would need multiple smart NiMH battery pack discharge units... if you are doing the 12 cell - 2 sub-pack option you would need 5 Discharge units... and if doing the 6 cell - 1 sub-pack option you would need 10 discharge units...

If the discharge units you pick happen to also be smart multi-cell battery pack charge units as well than you can skip the HV ~300mA charge and just use the same 1/2 then 1/2 method for both charging and discharging.

I would suspect that the relay option with just one smart charger / discharger would be a less expensive way to automate the process ... but it will take much longer .... but it is all automated so I guess the time factor matters far less.

this was my ramble.

[retepsnikrep]

All good points gents, but I'm after an unattended automatic solution that can determine all the info we need including.

Subpack charge capacity at 5ah rate
Subpack discharge capacity at 5ah rate
Subpack self discharge rate
Number of cyles before no further improvement in specs.

It will record this data and be available in a text file we can glance at for a full pack report at the end of a week say. The time doesnt matter that much and it's easier for my choosen pic/axe to manage one charger/discharge circuit.

It will allow simultaneous charge/discharge from different subpacks. So after you have discharged subpack 1 at begining of test you can then be charging it whilst no 2 is discharging, that will speed things up by 50%.

I realise it's quite relay intensive but you can get some pretty powerfull small relays nowadays.

[Roger Crier]

When are you planning to fit the "Insights R us" neon sign outside your house! Any more projects and you will be able to apply for EU funding of one sort or another. In fact with the big boys in the auto industry in the deepest of doo doo's at the moment, you may find you are the UK's only viable auto industry soon.

Sounds like a good idea to me. I think those magnetic connectors you mention are readily available from RS etc.

If I can help in any way with replacement end covers or tough insulated foam board, then just ask.

My battery seems to be trouble free, especially now MIMA has been working it a bit harder, but I would like to give it a bit of an MOT soon, just to see how it is compared to a 100% fit battery.

So given the low (ish) cost of this project, it should appeal to quite a few of us as long as you present it in a "Blue Peter" sort of format so people are not scared off by it's apparent complexity........we are not all "ace dibs" programmers and I don't think you fully grasp how "Greek" it all sounds from a layman's point of view!

[JimIsbell]

I have designed, but not yet built a dynamic balancer that will ride along with you keeping the battery in balance ALWAYS.

In support of this I have just finished, an hour ago, a Data Port on the outside of the battery box that will allow me to connect, the instruments I am designing, to the battery without removing the cover. Balancing will be done through this port as the balancer I have designed is for continuous use, not for hit and run as the previous balancing has been done.

I have nothing against Hit And Run, in fact the battery I did this on last month has now been running for over a month now with only 2 RECALs in the first few days. It has been stable since then running from 7 bars to 20 bars and back many times. I have not tested the bottom to see how far it will go, but remember, this was a battery declared dead by the dealer and left to rot for some time in a garage.

However, after the original Hit and Run, I think its life will be greatly extended by dynamic balancing.

Pictures of my Data Port installation can be seen at Picasa Web Albums - Jim they are the last three pictures in the Honda Insight album.

[retepsnikrep]

That's good jim.

My comments are.

It requires a mod to the battery fixing the connectors and the data lead.

Can you access individual supacks with your system?

Can you post more details/schematic of your actual dynamic balancer on your thread?

If between us we come up with a couple of different solutions that's fine.

I hope to eventually offer a battery swap out servcie to UK owners. I give them a balanced/cycled pack and then I do the procdeure on their unit and replace any bad sticks and pass the repaired unit on to the next person. I don't want to mod each battery.

[JimIsbell]

Originally Posted by retepsnikrep

Can you access individual supacks with your system?

yes. There is a line to each subpack. The wires are #22 so there is no need for fuses...#22 will fuse at 10 amps... Long before the 100 amp battery capability will be exceeded....

Originally Posted by retepsnikrep

Can you post more details/schematic of your actual dynamic balancer on your thread?

I will do that when the design is final. Right now I am still in the schematic stage and the actual components to be used are not yet determined. Its basically a capicitor storage shifting design that checks and redeposits a small amount of charge 2,000 times every second so that the battery always stays in balance.

Originally Posted by retepsnikrep

I hope to eventually offer a battery swap out servcie to UK owners. I give them a balanced/cycled pack and then I do the procdeure on their unit and replace any bad sticks and pass the repaired unit on to the next person. I don't want to mod each battery.

I can understand that. Modifying the battery is not a lot of work but it is extra if the person receiving it isn't going to use it and doesn't want to pay for it. It took about 3 hours total time to do the mod including the "through chassis" connector...if you don't count the taking out and putting back of the battery which you would be doing anyway if you were refurbing a battery. The total parts cost was $5 for the barrier strip, $1 for the printer cable at the thrift store, about $3 for some wire and the solder on connectors and $6 for the "through chassis" connector. It would take less time and less money if the cable was just directly connected to the subpacks, but I wanted heavier wire to the subpacks from the barrier strip so that I could run heavier currents on them for the initial balancing where I run a discharge of 2 to 4 amps. The printer cable is designed only for data transmission and for the dynamic balancer which will not be high current.

My main reason for doing this is that I am heading toward a 3 or four battery car and the data cables will be run to a 4 port data switch, available at the thrift store for $3, so that I can check the health of all the batteries without removing them and so that I can ballance them without removing them.

[Hybrid-Battery-Repair]

Originally Posted by retepsnikrep

You want to avoid taking the ends off IMHO. It's a right pain, time consuming and easy to damage the ptc ends especially if the process needs doing every couple of years to keep an old pack in shape.

That's why I suggested a plate be installed with no battery-to-battery interconnects, but with the PTC strip connections installed. It would be done once and left there. Then you could slap one of two plates over that. One would form the normal interconnects and be left on. The other would have your tester.

Originally Posted by retepsnikrep

I think it's best to do the sticks individually or you can't isolate a bad subpack without doing further work. This system will show up bad subpacks without extra work. I want it super simple to connect and operate.

I'm finding that the most critical bit of information is the individual charges on the batteries after use but prior to charging/reconditioning.

Originally Posted by retepsnikrep

I don't know about your experience but are there actually many bad subpacks (dead cells etc) or is it just they have gone out of balance.

I'm finding that they don't go out of balance without a reason. Either a cell becomes diminished in it's capacity and then takes less and less charge as it death spirals down, or it is forced to under or over charge by the batteries next to it. Also, it's almost never more than a few cells.

I'm receiving another pack for rebuilding in a couple days. I'm going to try working on it as pairs where I recondition the pairs that seem good and individually the cells that don't. This is to try to reduce the 18 hour per cell cycle to something a little smaller (cut 3 weeks down to 2). Alternately, I'm going to have to get a second charger so that I can do two cells at once. I've also decided, similar to your extra packs, that I'll have to pre-test and match up sets of batteries to allow me to do a swap-out for customers that don't want to wait three weeks for their pack to be fixed.

FYI, I've settled on the name "Northeast Hybrid Battery Repair" as I'll probably branch out into Prius batteries later.