grid charger/balancer

[Mike Dabrowski 2000]

The resistor can be any low value (10-200ohms) but as Uhtrinity pointed out, it will disapate a lot of heat. The idea is to soften the adjustment of the output current, so it does not change so quickly as the variac is adjusted. It works without a resistor, but the adjustment is a bit touchy.
The LM317's are dissipating the same amount of wats as a resistor would, so this method of current control will always simply waste the regulation elements voltage drop at current as heat.
The led supply of this multy supply grid charger uses high frequency PWM switching to regulate current, so much less heat is generated/wasted in the charging process.

JimIsbell,
If you read this thread carefully, you would know that this grid charger will charge the whole pack at the same time, not individual subpacks, don't know where you got that idea?

An important consideration with this grid charger is how the constant voltage supplies are adjusted to set the minimum pack voltage that will retain CC operation.The CC supply will adjust it's output voltage between ~4V to 48V to maintain current control. If as Uhtrinity indicates the max charge voltage we want to see on the pack is 175-177V, we can adjust the three 48v constant voltage supplies to 43V each for 129V which with the max 48v output from the constant current led supply will set the maximum full current charge for the combined charger to 177v, at which point it will quickly taper down the current if the voltage rises beyond that point. We found that the 169-171V point was where the pack voltage was pretty stable and the rate of change had dropped to the point where we felt the pack was fully charged and balanced.
Since the three 48V supplies cannot be adjusted to 40.6v to limit the max voltage to this 170V limit, I added the two diodes that Peter suggested which dropped the voltage by about 1.2V, and a series 1W led that drops an additional 3v, which has the effect of reducing the whold supply output by about 5V and allows us to limit the max voltage to the 170Vdc full charge point with adjustment of the three 48V supplies.
I will put up a modified schematic later today.

[uhtrinity]

Originally Posted by Mike Dabrowski 2000

The LM317's are dissipating the same amount of wats as a resistor would, so this method of current control will always simply waste the regulation elements voltage drop at current as heat.

Actually the LM317hv's produce very little heat even at peak draw (~135 watts). I figured out the power loss to be around 30% with the resistors. In comparison I only lose about 5% or less with the LM317's.

[Mike Dabrowski 2000]

the heat will depend a lot on the difference in voltage between the charger and the battery.
The part is just a linear regulator, so except for the 3V forward voltage drop of the regulator it is acting like a resistor that is adjusted to just produce the 350ma. it is always just right.

The fixed resistor will only be at 350 ma at one voltage difference, and will be sensitive to battery voltage and need frequent adjustment to maintain the 350 ma.
Constant current source with LM317
Nice to hear that your charger is working out so well.

[Mike Dabrowski 2000]

schematic with diodes and led current indication.
http://www.99mpg.com/Data/resources/...balancer_2.pdf

[3-Wheeler]

uhtrinity,

Thanks for the information about not needing a step transformer. My line voltage tonight measured 122 VAC (though not always the case), and with the Variac plugged-in and adjusted to it's maximum, read 142 VAC. Dividing this value by the sine of 45 degrees gives a DC voltage close to 200. The variac should also have enough capacity, as it is rated at 10A.

So skipping the use of a step-up transformer basically saves me the cost of $25 or so. Thanks for the input on this point. Much appreciated!!

I also like the idea of using an adjustable voltage regulator, instead of a fixed resistor. Even if a resistor is dissipating 5 watts, that thing gets very hot to the touch, especially without any heatsinking. It seems that one regulator will work fine, since my current is much lower.

I already planned on using a 200uF-350V filter capacitor and adjusting the power supply output close to the battery voltage, attaching, then slowly increasing until 150 mA displayed on the VOM.

As Mike alluded, I will need to babysit the current setting as the battery tops off.

Jim.

[JimIsbell]

Originally Posted by Mike Dabrowski 2000

JimIsbell,
If you read this thread carefully, you would know that this grid charger will charge the whole pack at the same time, not individual subpacks, don't know where you got that idea?

Well, I got that idea because you said,

"Charging the whole pack with 350ma fan running, is different than charging subpacks separately."

Sooooo, I assumed that since I do mine as a whole pack that you must mean yours does it separately.

If you would "read this carefully......etc. ............# you would know that I charge the whole battery in series, about 200 ma for up to 24 hours....depending on how depleted it is. I DONT charge them separately!!!

[nemystic]

@#*! those dendrites, confounding those of us who drive the least in pursuit of a smaller ecological footprint!
The Li-Ion batteries I use for the commuting bike are much more considerate.

Thanks to Mike for assistance with this pack balancing experiment, and to both Mike and Ron for the advice in optimizing the result. I'm hoping to be able to post positive results with respect to expanded pack capacity in the weeks to come.
I hope that at least some of you will understand that extreme battery pack range cycling (while driving) is both counterintuitive and painful for hypermilers.
I had to drive to the Manchester, NH airport recently to pick up my son, and despite at least 25 stoplights on the back roads, I had about a 90 mpg trip indication with very little change on the iSoC.

While Toyota seems to have achieved a success formula with the Prius and Hybrid Camry, the "science" of affordable and highly efficient battery pack management seems to still be inexact at this time.
The challenges GM has encountered with the Volt, and Toyota's return to NiMH, apparently being unable to make Li-Ion "bullet-proof" safe would seem to support this conclusion.

It's great to see Insight owners once again pushing the envelope with experiments that lead to more efficient solutions.
I haven't yet done the math, but at first glance, it seems like the balancing techniques discussed in this thread should yield a significant net benefit with regard to overall resource and energy efficiency.

Keep up the good work!

[JimIsbell]

Originally Posted by 3-Wheeler

As Mike alluded, I will need to babysit the current setting as the battery tops off.

You will find that the "baby sitting" is minimal. I set mine with the Variac to 200 ma and let it float. By the time the battery is full its down to 170 ma or so. Sometimes I try to keep it up near 200 for the first 5 hours by adjusting it about once an hour, but only if I have a severely depleted battery. Normally I just set it to 200 and let it sag to 170.

[retepsnikrep]

Just to clarify the purpose ot the two in4003 400v 3A diodes.

1) They are there to prevent power being available from the IMA battery outside the ipu compartment, and should be fitted as close to the power connections points as possible on the IMA battery inside the IPU compartment.

2) They prevent current flowing out of the battery back to the charger.

a) This helps prevent electric shocks from the IMA battery via the charging socket.

b) It also prevents a huge current rush from the battery back to the charger and the output filter capacitors when first plugged in. If this current inrush is not prevented it may damage the chargers and will certainly give you a surprise when you plug it in. (Flash/Bang)

[Mike Dabrowski 2000]

Peter,
The 1N4003 diodes I specified are 1A 200V, with a 30A surge rating.

Just about any standard diode with a minimum 200v reverse voltage rating and 1A or better current capacity should work.