Rapid Charger Electrical Efficiency

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I am monitoring the amount of electricity used by my 4.0ah and 2.0ah battery.  I have used the regular charger exclusively for several months.

Now, I've used the quick charger, and recorded 270 watts into the 4.0ah battery.  Which is much more than the battery capacity of 4.0ah @ 52 volts.

I know that some of the electricity is used to run the fan, and of course there is a bit of loss of efficiency with the charger itself.

But I'm wondering if anybody ever measured the amount of electricity going into the battery compared to the amount used from the outlet.  I would think this would be something good to know as people monitor their batteries.
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Kevin

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Posted 5 years ago

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Jacob

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Official Response
Your missing Root mean square(rms). This is the difference between AC(Alternating Current thanks Tesla) and DC(Direct Current, stupid Edison). Your measuring AC so to convert what the battery holds in AC watts you must multiply 270 by .707( or divide by 1.414). If you measured 270 watts, multiply that by .707 or divide by 1.414. This is the watt difference between a DC battery and AC charging. So 270*.707 =Equivilent to charging your battery with 191 watts so your battery had a little left in it. In electrical calculations, watts are watts, but a 4 ah battery at 56 vdc has 224 watts, it would require 224 watts * 1.414 317 watts measured in AC to charge with an AC supply.
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Kevin

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Thank you Jacob.  I knew there was a power differential between AC and DC, I just never thought about it being essentially 70%, which is pretty noticeable. 

But there still must be a less than 100% efficiency of energy to the battery, since some is going to run the fan in the Quick Charger, and both chargers must have less than 100% conversion efficiency.

In the Nissan LEAF it is actually less efficient to use the 120V charger than the 240V charger because of overhead energy usage by the LEAF to run the coolant pump.  So I'm just interested here with the EGO chargers, although the difference will be pretty small.
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Blue Angel, Champion

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No battery charging process is 100% efficient. There will always be some losses in the form of heat generation. I would assume that charging the battery pack at a higher rate (faster) would mean lower efficiency (more heat generated). If that's the case the standard "slow" charger, which is still plenty fast and much faster than any competitors charger, would be the more efficient way to charge. I own both chargers and I personally choose to use the standard charger since charging at a slower rate should be easier on the cells and extend their life... in theory anyway.

Also, Ego rates their battery packs the same way DeWalt and several other companies do, using 4.0V per cell. The Ego batteries use 14 cells in series at 4.0V per cell to generate 56V. DeWalt and others do the same with their "MAX" batteries, like the 20V MAX cordless drill batteries.

This is actually false marketing as the average voltage of the cells is 3.6V during normal operation (3.0V depleted, 4.2V charged, 3.6V average). That's why most drill batteries are marketed as 18V, five cells in series at 3.6V per cell. Bosch actually explains this on the box of their 12V cordless tools.

Judged by the same 3.6V per cell, the Ego batteries would be 50.4V instead of 56V, and the 40V competitors would be 36V.

This also comes into play when looking at the energy capacity of the battery pack in Watt-Hours. Pack voltage multiplied by the capacity in Amp-Hours equals total Watt-Hours, so 56V x 4.0Ah = 224Wh. In reality, it should be 50.4V x 4.0Ah = 201.6Wh.

Lots of different companies are rating their batteries this way so it's no surprise to see a new line of power tools following suit. Until there is some form of regulation on advertised battery capacity this will continue to be the case.