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Discussion Starter · #1 ·
I have never done this process but have read a lot of posts. Always wondered about discharging with the lightbulbs. this is a slow discharge process. does it have to be slow. I know throwing the discharge switch on the battery pack reaches the same goal almost immediately. could someone comment on this, or is it too dumb a question ??
 

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If no one has mentioned this before, WELCOME to the forum.

I have never done this process but have read a lot of posts. Always wondered about discharging with the lightbulbs. this is a slow discharge process. does it have to be slow.
Yes absolutely. There are chemical reactions going on inside the 120 cells that need to take place to balance the cells.

I know throwing the discharge switch on the battery pack reaches the same goal almost immediately. could someone comment on this, or is it too dumb a question ??
It's not a dumb question, but you do need to read more about charge/discharging the battery.

That switch is not a battery discharge switch. It is the IMA battery master ON/OFF switch.

I have an article about building your own charge/discharger on my website. The article also include a lot of information of what, why and how to do a proper charge and discharge (and why it is a slow process).

You can get to my website by clicking on the "CRX" area just below this post.
 

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this is a slow discharge process. does it have to be slow.
I'm trained in the school of @olrowdy01, so my answer is similar to his. Slow is good - it gives time for the chemical processes to unravel without forcing any single cell into a damaging state.

There are a lot of "theories" out there about battery conditioning. Some, like @eq1, are strong advocates for reconditioning individual sticks or taps. It's more technical, but probably better if you have the skillz.

There are now folks who propose bringing the battery down all the way to 0 with a dead short at the end. I haven't been that brave yet. But even then, they still suggest going slow to get to that point.

Slow is your friend, and the time is worth it. Think of it this way - a new pack is going to cost $1500-$3000. If you can recondition an old pack in a week's worth of time, that's $9 to $18/hour if you worked at it 24 hours a day. In reality I put maybe 10 hours into overseeing the process in a week, so my time is worth $150/hour. Whoo! 😜

- Park
 

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Discussion Starter · #5 ·
I guess the red switch discharges some capacitors. then if the voltage measured at the junction board terminals in the IPU unit is below 30V its safe to remove the battery module, dont know about just poking around. If voltage is above 30V it indicates a problem with IMA system. SERV, BULLETIN 06-057. Mabey not pertinent to the topic but,,,,,,,,,,,,,,,,,,, thanks to everyone for your input.
 

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Just want to add some thoughts/clarification to the whole "slow discharge" idea. Having done this stuff for quite a while now, I think I have a decent idea how 'all this' works...

The discharge doesn't have to be slow, exactly. If you were trying to recondition a single cell, you'd have to drop the load/current really low once it seemed near empty at the higher rate. So you discharge to 'empty' at the higher rate - whatever, start at say 6 amps, move to 1 amp - and then you'd need to go even lower, as low as you can stand to wait for. I think the main problem is that Insight NiMH cells have a variable 'stoichiometry' - basically the main reaction doesn't happen at a single voltage, it can happen within a range... I think over time and usage, more and more of the nickel (hydr)oxide ends up at a lower oxidation state and that pulls the voltage down, lowers the power output. It's like you end up with two pools of reactants that both contribute to the overall output, a 'high' pool and a 'low' pool, the more low you have the more it drags down the overall voltage and power output capability. That's why once the cell nears empty at the relatively higher load, during your reconditioning discharge, you need to drop the load drastically; that will be able to discharge the 'low pool', then you'll be able to recharge that pool and it will return to the higher level... That's the main 'chemical-level' reason for quote "slow" discharging. But it's not exactly slow, it's just that you need to drop the current really low at the bottom end... Discharging at a low rate from 'full' isn't necessary...

Practically speaking, you can leave the car in auto-stop and let the 12V system load discharge the IMA pack, you don't need to do say a low current lightbulb discharge all the way from the top. Drive the car, use a lot of assist, pull into your driveway with headlights ON and let the car do auto-stop, leave it in AS until either the 12V battery warning light comes ON or the dash BAT gauge drops below 3 bars (usually you'll see the BAT gauge drop first). Then you can do your super low current discharge, like with an 11W oven light bulb. At this point one of your cells is functionally empty at whatever current rate you used during the auto-stop discharge. With no accessories ON I think it's about a 0.5 amp load. I have always-ON driving lights so the lowest I see is about 1 amp. Both of these are pretty low already. With reconditioned cells, there's only about 2-3% capacity left. But that's the thing: With non-reconditioned cells you can have 25-35%, even more, of the capacity locked up - the cells will seem empty at say 1 amp, but only because so much of the active material is degraded, at that lower oxidation state. That's the stuff you need to discharge at a super low rate to get your capacity and performance back.

I guess I should at least mention one other thing: imbalance. I've been talking about cell-level, electro-chemical level reconditioning. The other level is pack-level. You can have reconditioned cells, but the pack as a whole can still behave badly because cells are charge-imbalanced. Some cells aren't charged as high as others. In the above scheme, it'd probably be best to start with a full grid charge to try to maximize the raw charge balance of the cells as much as possible. So you'd grid charge first, then drive, use assist, leave in auto-stop, then very low wattage bulb discharge. The alternative - and my preference - is to discharge taps rather than putting an 11W bulb on the whole pack.
 

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Discussion Starter · #7 ·
Just want to add some thoughts/clarification to the whole "slow discharge" idea. Having done this stuff for quite a while now, I think I have a decent idea how 'all this' works...

The discharge doesn't have to be slow, exactly. If you were trying to recondition a single cell, you'd have to drop the load/current really low once it seemed near empty at the higher rate. So you discharge to 'empty' at the higher rate - whatever, start at say 6 amps, move to 1 amp - and then you'd need to go even lower, as low as you can stand to wait for. I think the main problem is that Insight NiMH cells have a variable 'stoichiometry' - basically the main reaction doesn't happen at a single voltage, it can happen within a range... I think over time and usage, more and more of the nickel (hydr)oxide ends up at a lower oxidation state and that pulls the voltage down, lowers the power output. It's like you end up with two pools of reactants that both contribute to the overall output, a 'high' pool and a 'low' pool, the more low you have the more it drags down the overall voltage and power output capability. That's why once the cell nears empty at the relatively higher load, during your reconditioning discharge, you need to drop the load drastically; that will be able to discharge the 'low pool', then you'll be able to recharge that pool and it will return to the higher level... That's the main 'chemical-level' reason for quote "slow" discharging. But it's not exactly slow, it's just that you need to drop the current really low at the bottom end... Discharging at a low rate from 'full' isn't necessary...

Practically speaking, you can leave the car in auto-stop and let the 12V system load discharge the IMA pack, you don't need to do say a low current lightbulb discharge all the way from the top. Drive the car, use a lot of assist, pull into your driveway with headlights ON and let the car do auto-stop, leave it in AS until either the 12V battery warning light comes ON or the dash BAT gauge drops below 3 bars (usually you'll see the BAT gauge drop first). Then you can do your super low current discharge, like with an 11W oven light bulb. At this point one of your cells is functionally empty at whatever current rate you used during the auto-stop discharge. With no accessories ON I think it's about a 0.5 amp load. I have always-ON driving lights so the lowest I see is about 1 amp. Both of these are pretty low already. With reconditioned cells, there's only about 2-3% capacity left. But that's the thing: With non-reconditioned cells you can have 25-35%, even more, of the capacity locked up - the cells will seem empty at say 1 amp, but only because so much of the active material is degraded, at that lower oxidation state. That's the stuff you need to discharge at a super low rate to get your capacity and performance back.

I guess I should at least mention one other thing: imbalance. I've been talking about cell-level, electro-chemical level reconditioning. The other level is pack-level. You can have reconditioned cells, but the pack as a whole can still behave badly because cells are charge-imbalanced. Some cells aren't charged as high as others. In the above scheme, it'd probably be best to start with a full grid charge to try to maximize the raw charge balance of the cells as much as possible. So you'd grid charge first, then drive, use assist, leave in auto-stop, then very low wattage bulb discharge. The alternative - and my preference - is to discharge taps rather than putting an 11W bulb on the whole pack.
are those the taps in the IPU
 

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The only taps I'm going to be discharging have IPA flowing through them.
 
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