Battery discharge at constant watts with iCharger 4010DUO

pickworthi

100 W
Joined
Oct 1, 2020
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129
Location
UK - Oxfordshire
I recently acquired a Cycle Analyst and Baserunner, and noticed that they provided the ability to limit maximum power, as well as maximum amps. I have a 36V (10S) e-bike conversion, and the idea of getting constant peak power delivery over a full ride discharge is attractive to me. My current KT type controller is limited only by amps (15A), and thus power varies from around 600W when the ride starts to around 480-490W when battery is depleted (as voltage sags). Also, power drops on a climb as the voltage sags. A steady 500W max should give a more consistent ride experience - at least that's the theory.

Before trying this on the road, I wanted to test whether my batteries would be happy with a steady 500W load. I was a bit stumped, since test equipment I have can do constant current or constant resistance discharging, no obvious way to get a constant power discharge.

It then occurred to me that my iCharger 4010DUO might be able to do this. Long story short - it does. I love my 4010DUO :).

<TLDR>
Basically, use regenerative discharge mode, set the resistor load maximum Volts and Amps to give a bit more than a 500W limit, set the discharge current high enough to drive the resistor at maximum power through the whole voltage range, and start a discharge.
</TLDR>

Long story:
1) I have a resistor load I built from an Ikea desktop fan heater. My multi-meter says it is 1.8 ohms. I have tested it up to 600W, and it is comfortable in the 500-600W range. I plugged this into one of the 4010DUO channels.

2) On the other channel, I set up the battery discharge to use the regeneration channel method, and set the limits for this to 31V and 17A. From the experiments I did it appears that the prime limiter to watts on the regeneration channel is voltage, 31V got me just over 516W. I haven't played around to fine tune this to exactly 500W, but I think it might be possible.

3) I set the battery discharge current to 20A. The 4010DUO will not reach this since the total power output is limited by settings above - but it will keep trying, thus keeping the power at the maximum it can achieve.

Starting a discharge with these settings, the current starts low, and then ramps up smoothly until 516W is reached. It then maintains 516W until the cell low voltage cut off is reached.
At low voltage cut off, the iCharger goes into a constant voltage mode until it reaches the current cut off. Incidentally, this provides something a little bit similar to the Cycle Analyst low voltage throttle roll off function - for a short while at least.

I have included two graphs of this discharge run below. The second graph shows the 10 individual cells voltage tracking down together, which is nice. My conclusion is that a steady 500W discharge will be OK with this battery, as long as I set throttle roll off at a suitable point (still to be experimented with).

The test was inspired by a scenario in which I set off up a hill steep and long enough to require full power without interruption.
Question: how long would I go before the battery is depleted?
Answer: about 38 minutes.
This will not, for example, get me up Mount Hamilton, should I ever visit the Bay Area again. It will be ample for all hills in my local area though, which is nice to know.

This approach to get constant power (watt) discharge will only work if you can isolate 10 cells (or less) at a time, have external balance connectors, and (of course) own a suitable iCharger.

Screenshot_2021-07-29_12-08-37.png

Screenshot_2021-07-29_12-10-34.png
 
Nice charger, not only for RC use.
 

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