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Sep 13, 2004, 11:12 AM
Texas Ranger
Neil Walker's Avatar

Discharge cutoff voltage - loaded or unloaded (specs/charger/esc)

OK, I'm confused. There are many places where you need to know/set a cutoff voltage for discharge. LiPo packs say don't discharge below X volts per cell. Spec sheets on NiMh batteries (like KAN 1050s) say 1.0V per cell cutoff on the charger. Setting the pack cutoff voltage on your ESC with BEC. Setting the cutoff voltage on your charger.

It's never really clear to me if any/all/some of these mean loaded or unloaded voltage. I have a Triton charger, and it seems to measure the cutoff voltage when discharging under load. (conversely when detecting the peak voltage it appears to remove the current periodically and check the voltage for a few seconds so I assume it's trying to detect the peak under no load...) So if, for example, I set it to 1.0V/cell (what the KAN spec sheet seems to suggest) when discharging a KAN 1050 pack, it cuts off very early in the discharge cycle - earlier the higher C you discharge at. Strangely enough if you use the Triton's "cycle" feature the manual says the cutoff voltage is fixed at 8V/cell. So looking at a battery spec sheet and discharging on my chrager to evaluate the performance of one of my packs I'm not really sure what I should be setting the cutoff at to A) accurately guesstimate how the pack performs and B) Not discharge my MiNh pack too far.

Then I'm also not sure what I should be setting the cutoff on my ESC/BEC to as well. 10-cell NiMh pack. Obviously under load on the motor the voltage is going to drop lower, but then if the motor cuts out it should come back up under the miniscule load from the receivere/servos.

So could anyone explain it all to me, and when all the different types of "minimum/cutoff voltage/cell" means loaded or unloaded, and how/where to set the cutoff voltages on my charger/ESC?

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Sep 13, 2004, 11:30 AM
Registered User
When I first got into eflight I worried about this too. Turns out I was making a mountain out of a molehill. I discharged NiMHs and NiCds on my Infinity II to 0.8 and 1.0 volts per cell under load. I found only a 20-30 mah difference between the two extremes (7-8 cell batteries). Under 1 volt/cell I found it makes very little difference for the discharge cut off voltage. Currently I use 0.8 volts/cell and have never damaged any battery packs.

I don't know the answer to your other question about setting the motor cutoff on your ESC.

Sep 13, 2004, 02:34 PM
Texas Ranger
Neil Walker's Avatar
Thanks - so what you're saying is that under load once it hits 1.0V/cell you're basically done anyway.

Upon further thought I'm thinking the BEC question might depend on the current you're drawing? I'm at around 15-18 amps, if that matters to anybody.

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