I had a pack that I wanted to grid charge, and do a controlled discharge on, so I bullt a connector that allows direct tapping of the ten subpacks by duplicating the BCM connector.
It brings out the 11 taps on a .1" on center header that can plug into a breadboard.
made it with some extra connector pins and some epoxy putty.
Worked nice, just unplug the connector from the BCM and plug it into the adapter and your connected.
After the pack was fully charged,and was stable for a half hour, I set up a simple op amp circuit that held a latched relay on until the total pack dropped to 120V (1v/cell).
The relay discharged the pack through two 120VAC 100W light bulbs in series.
I watched the ten taps as the pack discharged and saw that one tap started to dive while the pack was still at 135V.
Stopped the discharge and recharged.
Be careful on the discharge, we really need to be looking at all of the subpacks to properly determine when to remove the load, or damage to the low subpack could happen.
Next step is to build a monitor that will stop the discharge when a subpack drops out.
too many projects not enough time. Still reorganizing the shop.
Using the figures for the last charge then discharge cycle (by which time the stick has stabilised with a steady final capacity) gives a Discharge over Charge ratio of about 93%.
My benefits do not last more than a few months.
Do you think the higher charge/discharge current of 10 Amps provides a better result for reconditioning than the lower value of 200 ma charge and 4 amp discharge that I am using?
If so, do you have any idea why?
__________________
Jim Isbell
2000, 5 speed, 250,000 miles
"If you are not living on the edge, well then,
you are just taking up too much space."
I watched the ten taps as the pack discharged and saw that one tap started to dive while the pack was still at 135V.
You can't assume they will all have the same capacity. I can GUARANTEE that they do not. I bring mine down to 0.9 V per cell, and you can only do that if you break it into more manageable chunks.
Can you discharge through the taps? If so, why not discharge each one to 14.4V?
Jim, your pack is becoming unbalanced because you have sticks that are significantly different than the others. You will never get it to stay stable until you replace the bad sticks. If all the sticks matched in capacity and internal resistance, you wouldn't have a problem. For those that don't drive their cars daily, self-discharge rates are a problem too, but I don't think that's your problem.
Measure the discharge capacity of each stick after fully charging that stick. This will show which ones are a problem.
Ron,
how big are the chunks that you work with, and what currents do you use?
I work with one stick (6 cells) at a time, but I can do two (12 cells) reliably.
With the one stick, I cycle at 10 amps and do high current discharge testing at 35 amps. (I've tried 50 amp and even 92 amp discharge testing, but I got no meaningful data.) I'm not comfortable going over 5 amps on two sticks.
My reasoning is that since my base unit is one stick, it will either perform or not. If not, I will replace it. If I can hurt that one stick with the chargers that I'm using, then the car will definitely kill the stick. Two sticks are another story because if they are mismatched, I can damage one simply because they are mismatched. When you get to 20 sticks, you are guaranteed to have some mismatching. It's not an issue for me, because when I'm done reconditioning each stick individually, I then swap them out with others to balance them.
If you can discharge through the taps, why don't you discharge two sticks at a time? Or perhaps do ten independent pairs at once? That way you could stop each pair when they bottom out. Alternately, open up the window end of the pack and attach 11 more taps and you can get to the single stick level.
Ron,
Sounds like the system your using should be great at determining the subpacks condition, and at the 10A/ 35A, you are giving it a nice exercise.
I want to know how far I can get without pulling the pack.
The discharge current through the resistors is pretty limited.
I will tinker in my spare time.
As Ron says, you can pull the pack and add 10 more taps. I have done that on all three of my batteries (actually I added 20 taps so I dont have to work 10 of them through a resistor). All are directly wired with wire to handle 50 amps. But if you dont have the time for it or the inclination, I understand. But disschaging them in pairs will allow you to drop to .95 V at the very least without much danger. I do mine individually to .9V and with direct connections I have the ability to discharge and charge at up to 50 amps...as long as temperature is watched.
Mike, I am posting on a new thread some questions about the OBD. If you have any knowledge of this interface I would like to have your input.
__________________
Jim Isbell
2000, 5 speed, 250,000 miles
"If you are not living on the edge, well then,
you are just taking up too much space."
Jim,
I remembered that you had tapped all subpacks, and of course I could do the same, but my thinking is that many packs that are just a bit out of balance, could be rebalanced in the car with a simple plug in balancing system.
The simple 350MA grid charger works nicely for the charge side, and when I get a spare moment, I am exploring ways to do a safe discharge without pack modification.
I expect that many people would use a plug in balancing system that did not involve pack removal, and if used on the pack before things got really out of balance could possibily avoid eventual pack failure and IMA codes.
Once the pack gets out of balance and codes are being set, a more comprehensive rebalancing is required, which will involve pack pulling and subpack level cycling.
Seems to work very nicely and assuming the overnight test goes OK I will be happy to supply and fit them for UK owners. You can get the supplies in the US as well from same supplier, perhaps we could/should think about a bulk purchase? I did discuss with the supplier in UK about price and possibly they could get it down to.
Quote:
For 100pcs, we could offer you a price of £10.90 per unit inc vat.
I am using the diodes in battery leads as before. I now need to find a nice neat enclosure to fit them into L200mm x W150mm x H100mm. I'm also using a 33R 25W resistor in series with them to limit the charging current when battery is at a low voltage to < 500ma which brings it down to the capabilities of the psu's. As the battery voltage rises the current falls away naturally anyway.
For this first test I set three of the supplies to mimimum output voltage and adjusted the fourth so in series they provide 170V no load output. Might adjust that up a bit later when I see how current has dropped as battery voltage rises.
Seems like a nice cheap option. 4 x psus, 2 x 400V 3A diodes and a 25W 33R resistor.
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