[SQUIGGLES]

Hi all.

I had started testing my circuit for discharging my pack as it is a pain in the butt to keep watching this thing, changing bulb's etc.

I am using 6 x 100 watt, 10 Ohm power resistor wire wound aluminum housed in series bolted onto a heat sink for the first phase of the discharge then 5 x 100 watt, 100 Ohm power resistor wire wound aluminum housed in series for the second phase also bolted onto a heat sink.

The design is a s follows:

If the voltage is above 140 volts it will begin the discharge cycle at 2.5 amps or 375 watts until it reaches 120 volts. Then the second discharge circuit will kick in at .25 amps or 29 watts till it reaches 70 volts. Then the 350ma charger will charge till 160 volts. At this point the discharge cycle will start again.

If it is below 140 volts when connected, it will charge to 160 volts then start the discharge. You can cycle it as many times as you wish.

Have a heat problem though. Those heat sinks get up to 110 degrees C, even with a 55 CFM fan on the first discharge cycle. Second cycle seems to be OK.

I am going to change the wiring connector from those ones on you find on eBay as I find those a little dangerous to say the least, if you use this please change yours too. They use 3 amps on the first cycle so I would rather use something rated for the draw and a screw on type for safety.

I would like to publish this to the community when I am finished so any input would be appreciated.

 

[S Keith]

Bulbs get pretty hot too. IMHO, I prefer bulbs because they don't have the same current taper as resistors. They're closer to constant current over larger voltage ranges.

I would caution you that you're likely getting reversals as high as 135-140V, and doing so at 2.5A is a bit higher than most's comfort zone.

IMHO, charging to only 160V is a waste of time. If you're not going to peak voltage, you're not top-balancing the cells. I'm sure there's some benefit, but I see it as very sub-optimal.

Steve

 

[SQUIGGLES]

Bulbs get pretty hot too. IMHO, I prefer bulbs because they don't have the same current taper as resistors. They're closer to constant current over larger voltage ranges.

I would caution you that you're likely getting reversals as high as 135-140V, and doing so at 2.5A is a bit higher than most's comfort zone.

IMHO, charging to only 160V is a waste of time. If you're not going to peak voltage, you're not top-balancing the cells. I'm sure there's some benefit, but I see it as very sub-optimal.

Steve

Thanks for your feedback.

Since I am still in the design stages these are all variables.

The charger can go as high as 180 volts and the discharge amperage's can be changed but the CC characteristic cannot. What are your suggestions on the peak voltages and discharge amperages?

 

[S Keith]

Unfortunately, not all packs peak at the same voltage, and it's influence by temperature. The guidance is peak voltage for 5-8 hours IIRC.

Alternatively, could you just time the charge for 24 hours?

 

[SQUIGGLES]

This is true.

After some research on the forums and the bench charge spread sheet of 2011 that I found, I will take a scientific wild *** guess at 172 volts cutoff.
Discharge will be at 375 watt till 120 volt then 25 watt discharge till 70 volt.
Your recommendations to me a week or so ago worked very well for me and are pretty close to the above.

Thanks once again for that.

 

[S Keith]

This is true.

After some research on the forums and the bench charge spread sheet of 2011 that I found, I will take a scientific wild *** guess at 172 volts cutoff.
Discharge will be at 375 watt till 120 volt then 25 watt discharge till 70 volt.
Your recommendations to me a week or so ago worked very well for me and are pretty close to the above.

Thanks once again for that.

Except you went significantly higher on the current. 2X 200W bulbs in series does not equal 400W load.

Many examples on this site of peak voltage <172V in cold weather. If you have to pick an arbitrary target, I'd make it 168V. That should get most to at least 80% SoC.

 

[jeff652]

This is true.

After some research on the forums and the bench charge spread sheet of 2011 that I found, I will take a scientific wild *** guess at 172 volts cutoff.
Discharge will be at 375 watt till 120 volt then 25 watt discharge till 70 volt.
Your recommendations to me a week or so ago worked very well for me and are pretty close to the above.

Thanks once again for that.

Aged batteries will commonly peak well above 172V. We set our chargers to 180V for a reason ;-)