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Old 03-21-2005, 11:03 PM   #1
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Default Step Charging

We have an upcoming new release of our TwoLane and Sportsman charger firmware, and wanted to ask about step charging.
Is this something that we should include in the new release?

I assume the purpose of this is to charge at a high rate until late in the charge cycle, and then step it down to reduce the overcharging/heating of the cells during the end of charge.

What interface would be best to specify the point to step down the rate? Should it be by charge time, bat temp, or ma?
One could allow all or a combination, like we do for peak detection, but I would expect something simple would be best.

Let me know what you think.
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Old 03-22-2005, 10:43 AM   #2
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Once you try the step charging you will never go back to anything else.

Most chargers that offer this do a 3 step profile where you define the step by ma, and in some cases turn on or off an inverse pulse option.

Typicaly for the new generation cells a profile such as:

7A to 2400Mah inverse pulse off ( turn inverse on to boost run time )
.3a to 2450Mah inverse pulse off ( seems to reduce IR and cool battery )
6A to 4200Mah, 18mV delta, or 45C (inverse is never used on peak step )

The main thing with the step charge is that you can charge your pack @ 7,8, or even 9A in the 1st step without harming it, use the 2nd step to help the battery cool and prevent a high IR build up followed by a convetional peak step. After its finished you have a pack with lower IR and higher voltage that took in atleast the same capacity you would have with a convetional charge that finishes in less time.


Mark
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Old 03-22-2005, 11:53 AM   #3
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Mark,
Sounds good! I will add a multirate charge feature.
My concern with the described method is it's somewhat a return to the old Timed charger, where you need to specify/know the capacity and charge state of the battery you are charging.

Would you agree the best method for determining the rate adjustment would be the temp of the battery? Once it has a rise in temp, the second pause step would be invoked, followed by the low-rate peak charge. This way you can't make a mistake and cook the cells.
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Old 03-22-2005, 12:13 PM   #4
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Quote:
Originally posted by nimble
Mark,
Sounds good! I will add a multirate charge feature.
My concern with the described method is it's somewhat a return to the old Timed charger, where you need to specify/know the capacity and charge state of the battery you are charging.

Would you agree the best method for determining the rate adjustment would be the temp of the battery? Once it has a rise in temp, the second pause step would be invoked, followed by the low-rate peak charge. This way you can't make a mistake and cook the cells.

can u tell me what company u work for?
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Old 03-22-2005, 01:23 PM   #5
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Quote:
Originally posted by dakrat
can u tell me what company u work for?
I bet his screenname has something to do with it.
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Old 03-22-2005, 01:32 PM   #6
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Quote:
Originally posted by nimble
Mark,
Sounds good! I will add a multirate charge feature.
My concern with the described method is it's somewhat a return to the old Timed charger, where you need to specify/know the capacity and charge state of the battery you are charging.

Would you agree the best method for determining the rate adjustment would be the temp of the battery? Once it has a rise in temp, the second pause step would be invoked, followed by the low-rate peak charge. This way you can't make a mistake and cook the cells.
In general you will need to know what kind of capacity packs you are using for step charing to work so you will know at what point to change from 1 step to another. The ambient temp seems to have a huge effect on the packs temp during the early stages of the charge and thus would be far too inconsistant to vary the step by, in addition to the ambient temp variation you would create a problem for those who program the 2nd step as a cooling period. On the peak step ( 3rd step ) the peak detect should be by either voltage drop or temp just as your default method for a linear charge.
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Old 03-22-2005, 02:21 PM   #7
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Mark, I agree that temp values are not reliable if they are used as absolute values. We use a Delta Temp value for temp peak detect (with Absolute temp as a backup failsafe).
We can use the same delta temp for the step, i.e., the bat temp must rise by 6-degrees from the starting temp.

This is what I've got so far, to make it simple yet effective, is to have a Step delta temp, when reached, the amps are cut in half, and the step temp is doubled,
and the peak voltage detect is delayed for 60-seconds for the battery voltage to restablize at the lower rate.
This seems to work well, charge at 9amps, when the battery warms up, cut it to 4.5amps.
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Old 03-22-2005, 04:35 PM   #8
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The problem with a temp delta peak is that the batt temp will decrease during the 2nd step when running at the extra low charge rate of .2-.5A after the high 7-9A charge step.

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Old 03-22-2005, 04:59 PM   #9
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I would think it would be more of a problem if the battery was allowed to get hot enough during step 1 that it will cool to any significant degree during step 2.

The delta temp step method does not require a cool period per se, it goes from high rate directly to a lower rate, the battery temp would not go down if anything it will continue to rise slowly.
But if it did go down, why is that a problem? The high->low rate detection has already occured.

The period right after the lower charge rate must wait for the bat voltage to settle before resuming peak detect, or it will false peak as a volt drop occurs from the rate drop.

Cheers,
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Old 03-23-2005, 12:23 AM   #10
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OK, I have added BOTH delta temp step, as well as being able to specify a capacity charge to switch to the step 2 rate,
which is specified directly rather than just using half of the step 1 rate. A little more complex, but not bad. I like it.
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Old 03-23-2005, 09:33 AM   #11
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NIMBLE!

i will be racing at speedworld on sat, (weather permitting). I would love to talk about your chargers. Will you be there?
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Old 03-23-2005, 12:41 PM   #12
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Hello,
Unfortunately I will be in southern california this weekend, at Titus on sat night, and SoCal raceway on sunday.
I have trouble getting to Speedworld on saturdays, my son always has a baseball game on saturday, and my wife works many saturdays so I have my daughter to take care of also.
You'll find me at Cap city racing almost every Wed night.

Cheers,
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