Higher wattage is only for saving time. You can always use low wattage. 2-3X 40W in PARALLEL are additive. You could just use a 25W for the whole process. It will take the better part of 24 hours, but it will work fine.

Actually... your bulbs are 220V, no? If so, 40W is better. You could simply rig up 2X 40w in parallel until 158V remove one and continue to 105 or 66V as you prefer. Honestly, since you can go a few months between recalibrations, I recommend a two cycle discharge:

Grid charge for 24 hours.
Discharge to 158V at any wattage.
Discharge to 105V at 40W max (220V bulb).
Grid charge a minimum of 4 hours or 177V.
Disconnect grid charger.
12V reset and idle-charge in car 3X.
Reconnect grid charger and charge for 5 hours.
Repeat discharge program except finish at 66V.

The cycles don't need to be done consecutively, but that is best. Given the longevity of your pack since the last grid charge, it could likely be done up to 4 weeks apart and still get the same benefit.

Discharging only needs to be done when you detect reduced effectiveness of grid charging alone. Simply log the date and mileage of each grid charge and use a consistent criteria for grid charging, e.g., first recalibration, or two calibrations within the same week, one calibration per day, etc.

 

Yes, our bulbs work on 230V however, I was under the impression it made no difference what voltage you put through them as long as frequency is 50Hz.
Are you saying US bulbs are 110V specific?

 

Yes. Hz is mostly irrelevant.

Watts are a measure of power, P = I * V. For constant power, 220V current has to be 1/2 the value for 110V, thus they have higher resistance.

 

One learns something every day.Thanks for that!
Problem solved, two 40W bulbs will do the trick and are freely available.

 

UPDATE

charge - discharge cycle

It has been a year since I played with the battery pack. It's hard to take the car off the road for 24+ needed to complete the process. Plus the pack is behaving, only occasionally dropping to 2 bars.

I had a few days off work recently so, decided to build a discharger while the pack was being pre-charged.
I used a 2m length of 2 core appliance cable, 2 x 40W bulbs (230V) and 2 x bulb holders screwed to a piece of wooden off cut from a past project. The bulbs are wired in parallel and can work as a pair or one at a time. The device's cable terminates with a female socket taken from a computer mains power extension cable and mates with the charger's male.





Our temperatures have dropped to 5-8 C during the day with just over freezing overnight so, no danger of overheating.

Firstly I let the pack charge overnight, started at 20.00hrs with 174.3V and temp. 13.6C. By 23.00 it reached 187V at 11C and finished at 08.30 at 189.3V with 14.8 deg. C.

The discharge process proceeded immediately using 80W (both bulbs). It took 15 hrs for voltage to drop to 147V at 2.1 deg. C, so in future it needs more Watts. Looking at the rate I figured it was safe to leave it discharging overnight using both bulbs and then continue with just a single 40W bulb in the morning.
To my surprise in the morning, both bulbs were off with the voltage showing 23V @ 1.1 deg.C !!! rather than the anticipated 100-120V. It was one of those hot-cold moments.
The rate must have accelerated with voltage dropping and the near freezing temperature helped.

Anyway, back to charging, the voltage was back to 170V within 2 hours and reached 175V after 5 hrs, at which stage I performed SOC reset x3.
Took the car for a spin and it showed all 8 bars with only dropping 1 or 2 when accelerating only to recover quickly.
After charging for further 7 hrs the voltage showed 193V, which I had never achieved before so, happy bunny.
Deep discharge does seem to have an effect, wife drove the car yesterday and noticed the pack remained more stable than usual.

 

12.5 hr grid charge is decent. Better if it followed 3X 12V reset. You likely failed to get all cells to 100% SoC, but you probably got close.

For future reference, once you dropped under 158V (nominal) at such a low load, the battery was nearly empty and letting it continue overnight was not the right choice.

The rate does not accelerate; however, bulbs are more like a constant current load vs. a resistor that tapers linearly with voltage. For a bulb, a 50% drop in voltage results in a 30% drop in current. The VOLTAGE drop accelerated because more and more cells depleted and went into reversal.

Assuming you used 80W/220V rated bulbs, that's 0.36A @ 220V. 2 in parallel would be 0.72A; however, at lower voltage than 220V, this is probably closer to 0.6A average. 15 hr @ 0.6A = 9Ah, which is way over the rated capacity of the pack, so parallel doesn't make sense, or my calcs are off. 2 in series would be a measly 0.2A or so, which would only be 3Ah - much less than expected.

Whatever the case, taking 15 hours to get to 147V means the current was very low, so it's unlikely that you did any damage.

For future:
Series wire Ammeter into the discharge circuit to actually measure current. Cheap multimeter in 10A mode works.

1. 3X 12V reset
2. Charge to peak V for 5 hours, 24 hours max. Temperature drop can cause voltage to go higher. You want either constant or increasing temp above 10°C.
3. Drive the car, get it warm where it will go into auto stop. Run the A/C (not heat), blower on max, rear window defroster and headlights while auto-stopped until the engine restarts. This will discharge the battery to the ~20% SoC range while in-car in less than 1 hour.
4. Discharge w/high watt bulb to 158V.
5. Discharge w/low watt bulb (0.2-0.3A current, 1 of your 80W would do it) for 5-7hr AFTER it dips back below 158V. The idea is to pull about 1000-1500mAh out of the pack while below 158V nominal to reclaim lost capacity and minimize potential for damage with fewer cells reversals.
6. 5 hour grid charge
7. 3X 12V reset
8. 5-8 hour grid charge

This should take you less time and easily be done in a 48 hour period.

 

I have no idea whether the bulb rating was correct, they are marked with 40W stamp. Given these things are made in Asia, it wouldn't surprise me if they were made for both 110 and 230 V markets?

Can't say how grateful I am for your comments and tips. Especially, on how to deplete the pack in Auto stop. I will use this technique next time.

 

Okay. I see I misread your post. 80W was the total in parallel.


That would be about 1/2 of the 0.6A at 0.3A. 0.3A for 15 hours is 4.5mAh, which is right where I would expect it for a nearly fully charged pack. So, yes, those are 2X 40W bulbs rated for 230V.


No, you can't make bulbs rated for 110 and 230V. Bulbs are simply a resistive filament that obey Ohm's Law, V=IR and the power equation, P = IV.


40W = I * 230V; I = 40/230 = 0.174A


You can see if you change the voltage, you change the current. If you change the current, you don't get 40W.


Simply speaking, 230V rated bulbs have about 2X the resistance of 110V bulbs.


The Auto stop can be tricky, and it requires your attention. It can take some practice to get the A/C set to work, particularly when it's chilly like where you are. The Defrost setting may be more effective for you, but don't use heat as that will force the engine to run to provide heat. when you get to 3 bars, the gas engine will fire up and charge at about 4-5A.


It may take 30+ minutes depending on how much current you can pull out of it. You can set the parking brake and use a piece of wood or other implement to keep the brake pedal depressed.


Another option for discharge may be high wattage halogen lamps. Typical halogen work lamps can easily consume 500W or more. At the lower voltage, you're still looking at maybe 1.8A of current. That can accelerate your discharge to 158V to a couple hours.


You can essentially use any current you want down to 158V, and you can step it down to lower wattages to stay above 158V and accelerate the discharge. When operating purely below 158V, limit current to 0.2-0.4A and 5-7 hours UNDER 158V. Your existing 2X 40W setup should be fine for below 158V. The only issue I see is you ran it for longer than optimal.


As you do progressive cycles even on different weekends, you'll notice:


1) The time to discharge to 158V will INCREASE.
2) The 5-7 hours discharging below 158V will terminate at progressively lower voltages.


For the same load, you see a substantial increase in the discharge time to 158V on the 2nd cycle (20-30% or more). The 3rd cycle typically improves by about 10% or less. This is confirmation that your deep discharging is reclaiming lost capacity and reconditioning the cells.


Lastly, with an ammeter in the circuit (in series), you can directly measure and calculate the capacity of your pack.


Record time, voltage and current at:
5 seconds, 15 seconds, 30 seconds, 60 seconds, 5 minutes, 15 minutes, 30 minutes and every 30 minutes thereafter.


With that data, you can calculate the pack capacity AND the stored energy.

 

Thanks for the suggestions!

 

for grid charging in vehicle, couldn't the cooling fan be bypassed with a relay and the 12v provided to it?