low voltage cut-off - RC Groups
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Aug 28, 2017, 04:01 PM
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low voltage cut-off


Hi everyone. I'm an electric model boater. Purchased a couple Dimension Engineering CellShields. They are low voltage cut-off devices. It has a dial to set the cut-off voltage between 2.5 and 3.5 volts. I set it at 3.5. Fellow members of Offshore Electrics Forum recommend a 3.5 low voltage cut-off so that the resting voltage is around 3.7 volts. At 3.5 I cannot run the model as the low voltage cut-off kicks in almost immediately. So I called the manufacturer and asked them why it was kicking in so quick. They told me that they recommend a setting around 3.0 volts. I think I would destroy my batteries with that setting. I run revolectrix 420 silver graphenes 70c. 5,000 mah. 5s and 3s lipos. Any input is appreciated here. Thanks.
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Aug 29, 2017, 06:03 AM
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ggcrandall1's Avatar
You need to measure the current draw with a wattmeter. I suspect your current draw is high enough to suck the battery voltage down below 3.5V. Also you should verify that the LVC is indeed cutting out at 3.5V.

You could try running a pair of batteries in parallel. That would give you additional current.

Last you could post this in one of the boat forums. Someone there may have a setup similar to yours. It also helps to post links to your equipment. That way everyone knows exactly what you are using. i.e. boat, prop, motors, etc. The more info you provide, the less speculation in the replies you receive.

Glen
Aug 29, 2017, 09:58 AM
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Quote:
Originally Posted by urbs00007
Hi everyone. I'm an electric model boater. Purchased a couple Dimension Engineering CellShields. They are low voltage cut-off devices. It has a dial to set the cut-off voltage between 2.5 and 3.5 volts. I set it at 3.5. Fellow members of Offshore Electrics Forum recommend a 3.5 low voltage cut-off so that the resting voltage is around 3.7 volts. At 3.5 I cannot run the model as the low voltage cut-off kicks in almost immediately. So I called the manufacturer and asked them why it was kicking in so quick. They told me that they recommend a setting around 3.0 volts. I think I would destroy my batteries with that setting. I run revolectrix 420 silver graphenes 70c. 5,000 mah. 5s and 3s lipos. Any input is appreciated here. Thanks.
Cutoff voltage of 3.0v to 3.3v under load is quite common. You don't want to slow discharge to this voltage and leave it there for an extended time, but setting LVC there is fine. Even at 3.0v, you'll likely see the pack quickly rebound to around 3.3-3.5v after load is removed and the chemistry has a couple minutes to stabilize. Unless you are pulling light loads (typically not the case with a boat), having LVC at 3.5v is going to terminate too early. My recommendation would be to lower LVC to 3.2v (and then maybe 3.0v) and see if you notice better runtime. Check the cell voltages after they cool for a couple minutes and see if they rebound to around 3.3-3.5v - if so, you are all good. Also make sure all cell voltages are roughly the same after discharge - if one cell is significantly lower or dropping below 3.0v at rest, then that may be a weak/bad cell and a lower LVC cutoff is only going to shorten its life.

For best battery life, let the pack cool for several minutes, then do a 1C Storage charge to bring the cells back up before putting it away for the day.


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