Possible to change low voltage protection? How?

Chalo

100 TW
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Apr 29, 2009
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Austin, Texas
I have a battery of 104V nominal, 117.6V fully charged. I've been able to use it as a portable substitute for household power, but so far my attempts to use it as a light EV battery have hung up on the controller. I've wanted to find one that can tolerate the high voltage, but not demand more power than the battery can supply or than the amount I can use.

I recently found, and ordered, this controller:
https://www.ebay.com/itm/120V-1500W-Electric-Bicycle-E-bike-Scooter-Brushless-DC-Motor-Speed-Controller/142990552133

On poring through its description, I found two items of concern. The first is this:

Soft Low-Voltage: When the battery voltage become lower, the current will also become lower to keep normal running. It not only protect the battery and extend the battery life, but also increase the running distance.

And the second is this:

Over voltage and low voltage protection

If this controller is set up for ten 12V SLA batteries, as I expect it to be, then the implication is that it will cut off at 105V, which is higher than my battery's nominal voltage. I have asked the seller, but have not gotten back a reply, as to what voltage triggers the "soft low-voltage" mode.

My question is this: Is it possible for an end user to lower the voltage at which these features become active, or eliminate them entirely? And if so, how? I don't even know how a motor controller senses voltage, so I don't know where to start.
 
There should be an voltage divider inside by modifying that you should be able to use lower voltages. Ill post a video if I can find again from the youtube.
 
ZevEst said:
There should be an voltage divider inside by modifying that you should be able to use lower voltages. Ill post a video if I can find again from the youtube.

I didn't think to check YouTube for that, but thanks to your hint, I was able to find this video:
[youtube]3f6nKJp182E[/youtube]

It runs too fast for me to make sense of it on a first pass, but once I get the controller in hand, I'll watch it some more until I unravel it. Lucky for me it seems as simple and cheap as adding a resistor; no SMD soldering necessary.
 
Chalo said:
If this controller is set up for ten 12V SLA batteries, as I expect it to be, then the implication is that it will cut off at 105V, which is higher than my battery's nominal voltage.

I received my new controller and was surprised at its stated specification:


Voltage: 120V
Power: 1500W
Current limiting: 42A
Under limiting: 58V

It makes me wonder what kind of battery this is supposed to work with? The cutoff voltage is too low even for 72V SLA, but it's a 120V nominal controller. The good news for me is that I don't have to modify it.

Also, I wonder how 120V times 42A somehow makes this thing a "1500W" controller. 30% motor efficiency?
 
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