12/3 is good for 20A. Massive overkill.

Regardless of the wire gage, your typical cheap multimeter with 10A current function can readily handle <2A indefinitely even with the thin leads. The internal shunt on the 10A circuit is at least 18awg. Given that you're going to be using very low currents, anything 28awg or heavier should suffice.


If you're worried, just feel the wires for heat. If they never get more than comfortably warm, all is well.


The purpose for the ammeter is to measure the current flowing so you can compute capacity.

 

I don't plan to leave the pack in the car, but I was looking at your google doc about DIY grid charger building and found a question, the power supply you suggest to drive the in-vehicle battery fan -- what does that fan run on? 144VDC (ish)?

I got a box fan I'll setup blowing on the pack but I was curious.

 

Powered by the same AC as the HV supplies.


That document is horribly outdated. I need to update it.


That 12V PS is really only appropriate for the G1 Insight. It won't drive a HCH fan adequately.

 

For some reason I forgot about the capacity calc.... I remember you guys talking about the discharge time but don't know where my head went when it came to the amps part of the equation.

Bummed because I got a cheapie power socket... don't know what gauge wires are meant to be shoved in the holes in the back but its smaller than the probe tips on the VOM's, rats, that would have been so clean, no cutting, could have reused the VOM;s for something else later... (although this will likely not be a one time thing either I suppose...)


Yeah I was going to set the wires right where the fan blew on them too just to be safe. I got romex laying around so figured why not use it for everything else.... but the meanwell and the ampmeter are both strand so I'm now second guessing that idea.

 

Periodically document time, voltage and current. From that you can compute actual capacity and establish a performance baseline for future efforts.


After 3 cycles, if you discharge to 144V and compute a 4500mAh capacity, you can always have an idea on the future health of the battery. if you repeat a grid charge/discharge to 144V 6 months later and see that the capacity is 4200mAh, you probably don't need to continue with the reconditioning.


It's also VERY useful seeing how the various cycles compare. When you see your gains drop dramatically, you know you don't need another cycle, e.g., 1st cycle = 3500mAh to 144V. 2nd cycle = 4500mAh (29% improvement). 3rd cycle = 4900mAh (9% improvement).


There may be more to be gained, but it's likely not worth the effort.


Note that it's extremely important to grid charge for 30 hours @ 350mA after each discharge.

 

QUESTION:
I need to be sure I understand how HA defines a discharge. https://hybridautomotive.com/pages/sd#wattage

My understanding was we take the thing down to 96V ( for hch1) then recharge it to full, then discharge to 60v, recharge, and then discharge to 12 and then recharge (for 30 hours this time) The point where I think I may be misunderstanding is with the battery at 96V, wouldn't that take far less than 30 hours to get it back to theoretical max (on this and the second discharge)?




Where do you stand on double vs single bulb, Steve?

I have two 60 watters but am unsure if i need to go buy one or two 40's and 25s... need to check the halogens to see what they pull.

LOL I see you updated your sig until you have time to update the doc.

 

I always use two bulbs in series.


Yeah, my work blocks access to both google drive and dropbox... I'll forget when I get home.


2X 40 halogens in series should behave like 2X 27W incandescents in series. I wouldn't bother with 25W.


When a NiMH cell is discharged to 1V, it is empty.


When you discharge at LOW current to less than 1V/cell, it's a very reasonable expectation that you have many depleted cells in full polarity reversal.


The ANSI standard for NiMH capacity determination is 0.2C discharge to 1V/cell, 0.1C charge for 16 hours (1.6X capacity = 10,400mAh input), 0.2C discharge to 1V/cell.


You're at about .05C, so you need to go 30 hours to get 10,400mAh any time you discharge to below 120V at < 0.2C.


It's far from exact, but a little overcharge to guarantee that all 120 cells are at 100% SoC is better than having some undercharged cells.


30 hours @350mA gets you the 10,400mAh input.

 

I think I need a little more clarification, I just wish to fully understand.

I understand that at 0V (sum total of the 120cells) you very well could have half the pack reversed (equally reversed compared to the other half) but at 1V I get that you're out of what the car would see as useable energy but doesnt the fact that there is any voltage there show you still have some potential?

Charging to 1.6x capacity is assuming the .6 is lost as heat (or other losses) along the way right?
Also to counteract hidden (or mathematically cancelled) voltage from reversed cells?

As far as cell reversal I get the concept but when I try to visualize it (6 cells in a line discharging) I get lost as to how exactly even a cell in the middle could end up flipped since it has current essentially just passing through it (not camping out...ideally anyway) even flipped the individual cell has more potential than one which is completely neutral, its like a ball rolling down a hill slowly but then slowly rolling back UP the next one (works for inertia but I'm fuzzy on how it does with electrons!)

Lastly, when you say use 150watt bulb, do you mean thats the total amount of load (so 2 75's) or thats one of the two bulbs -- ergo use 2 150watt bulbs?
You're throwing me for a loop here because it is clear you feel the HA devices are very well made but for this application he only uses one bulb (it appears) https://hybridautomotive.com/collect...ant=5576544132


Again, not trying to bicker here, just want to better understand everything that I can so that I don't make any stupid mistakes.

 

Once a cell has no capacity remaining, it's voltage drops to zero. If current continues to be forced through it by the discharge of other cells, the polarity is reversed. You can think of it as + potential when it's contributing to the current flow and - potential when it can no longer contribute to current flow and is pushed the opposite direction.


Once a cell is no longer being driven in reverse, it's polarity will normalize and yield (+) voltage at the (+) terminal, but it will typically be under 1V depending on the duration of reversal.


I'm not sure what you're getting at with your 1V scenario. If you mean 1V/cell or 120V, it has nothing to do with the car and everything to do with the NiMH cell. The chemical reaction is what determines the potential, and once you hit 1V, the capacity yielding chemical reactions are gone (essentially).


Charging of NiMH cells isn't 100% efficient. It's very efficient in the operating range of the car, but It gets particularly less efficient as SoC approaches 100% and isn't particularly efficient coming up from 0% SoC. The reason for the long, low charge is to ensure all cells reach their true 100% SoC. The extra .6 is what ANSI believes is necessary, and for the most part, it's heat.


I'm more conservative than the HA guidelines. I use discharge times (computed discharge capacity) rather than target voltages because I can control the amount of capacity extracted when I expect cells are reversed in order to minimize damage.


I use two bulbs because I hate having one pop on me. A 110V rated bulb can pop readily when the pack is fully charged since you may be nearly 50% over rated wattage.


Any time I refer to a wattage, I'm referring to the bulb whether single or dual.


It helps to remember that two in series is like one of half the wattage, e.g., 2X 150W in series is like a single 75W.

 

Regarding dual vs single bulbs,

​​​​​i know if it was resistors when in series you add the resistance, but if in parallel you half it (two lanes = half the congestion) you guys are saying series but talking like its actually parallel.

How exactly do you wire the bulb circuit?
I have mine wired such that the current comes in one side of bulb 1, travels through bulb 1, from bulb 1 out Is a wire going to bulb two in, and then bulb 2 out is used to close the circuit.


Re 1v per cell, thats not empty, its one volt.
If by empty you mean below any usable SOC (Effectively empty for all intents and purposes) I understand that, but we arent looking at using it right now, we are trying to avoid overcharging is the primary concern I have.

I got the back all open, the mains appear to be 0v with the switch off. I thought I read someplace it just cuts the pack 60/40 with 40% still at terminals