Will regen damage an external wattmeter?

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E-HP   100 W

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Will regen damage an external wattmeter?

Post by E-HP » Jan 02 2019 3:58pm

My wattmeter, that's connected between my battery and controller via a shunt, stopped working a while back. I checked the connections, and things appear to be OK. The voltage reading still works, but amps, watts, and watthours just read zero (actually the watthours increments tiny amounts after a long ride). Thinking back, it failed around the same time that I had starting using regen, but not sure if that's coincidental. Is it possible to damage the current circuitry when the current is reversed during regen? I'm guessing no, since it seems like the measurements on either side of the shunt is really just a small voltage going the meter, albeit with the reverse polarity (which I guess could have caused damage).

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amberwolf   100 GW

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Re: Will regen damage an external wattmeter?

Post by amberwolf » Jan 02 2019 5:27pm

It's unlikely to be damaged by reverse current, unless it's really poorly designed (since reverse current would generate a reverse microvoltage across the shunt, but it'd have to have some really bad design or crappy parts for taht to kill the op-amp used to amplify that voltage so the MCU can read it.

I used to use a pair of Turnigy Watt Meters (which are not-so-good clones of the WattsUp) which have been cloned by a number of other companies, some ok, some worse than the TWMs. I had them wired in inverse series, IIRC, so I could read drive current usage on one, and regen / charging with the other. Never had a problem with that, on the 36v NiXX packs or the 16s LiFePO4 pack I used at that time.

I did eventually kill them with overvoltage, though--one with spikes higher than the 60v they're rated for, when using it with a 14s pack, and one by forgetting it's limit and hooking it up to an over-60v power source. I did that to a WattsUp, too.


But I havent' damged any TWMs or WU via reverse current--they don't respond to it, but they aren't hurt by it.

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Re: Will regen damage an external wattmeter?

Post by billvon » Jan 02 2019 10:01pm

E-HP wrote:
Jan 02 2019 3:58pm
Is it possible to damage the current circuitry when the current is reversed during regen?
For what it's worth, I used a power meter (a WattsUp) in line with some early ebikes. Regen didn't damage them, but I eventually blew one out (with symptoms similar to yours) with overcurrent.
--bill von

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neptronix   100 GW

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Re: Will regen damage an external wattmeter?

Post by neptronix » Jan 03 2019 12:22am

hm.. how many peak amps or watts of regen are we talking?
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Re: Will regen damage an external wattmeter?

Post by neptronix » Jan 03 2019 12:23am

what is your fully charged voltage as well?
Efficiency is everything :bolt:


My first major build: 8T MAC motor on a Trek 4500.
The new all-arounder: Leafmotor 1500w on a Turner O2 full suspension.
The monster scooter: ? on a Cannondale Semi Recumbent.

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Re: Will regen damage an external wattmeter?

Post by E-HP » Jan 03 2019 2:10am

amberwolf wrote:
Jan 02 2019 5:27pm
It's unlikely to be damaged by reverse current, unless it's really poorly designed (since reverse current would generate a reverse microvoltage across the shunt, but it'd have to have some really bad design or crappy parts for taht to kill the op-amp used to amplify that voltage so the MCU can read it.
That's what I thought. I think, per the specs, at 100 A, the shunt only has a 70 mV voltage across it, and I'm sure the regen current is way less than that.
billvon wrote:
Jan 02 2019 10:01pm
For what it's worth, I used a power meter (a WattsUp) in line with some early ebikes. Regen didn't damage them, but I eventually blew one out (with symptoms similar to yours) with overcurrent.
The current rating is 100 i?
|A, so probably not from overcurrent.
neptronix wrote:
Jan 03 2019 12:22am
hm.. how many peak amps or watts of regen are we talking?
Not sure, haven't measured it, but it's on next to the lowest regen setting of the controller.
neptronix wrote:
Jan 03 2019 12:23am
what is your fully charged voltage as well?
I charge to 57 volts on a 52 volt pack.

Thanks everyone. I think I'll troubleshoot the wiring again. Connections to the shunt look good, but the wire gauge is pretty thin, so maybe something broke under the insulation. I'll discon nect from the meter end and take measurements to see if there's a break or short.

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