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DC motor current draw

JNHEscher

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Curious what others' thoughts are on the amp readings of what I'm setting up as a radiator fan.

I put the component descriptions in the video. Didn't bother with showing the fan motion in the video as all you would see is a stroboscopic effect. You can hear what the motor and fan are doing over the wind pretty well. I did have a little trouble holding the leads of the yellow meter. You can see a couple instances of the reading dropping off when I lost contact.

What I'm wondering about is why the amps look just fine all the way up to the 75%ish mark of the potentiometer, but once I pass that and take it all the way to full speed, the amps immediately drop off and steady at around 1 amp. I didn't believe me meter at first, so I grabbed a neighbor's meter to compare to. Turned out about the same. Drawing merely 1 amp while churning this fan at full speed can't be right. The wind could be heard pushing against the fan and you could see the amps vary accordingly. Something seems off, though. What would it be?

20210411_175924[1].jpg
 
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FYI: You mention a video, but I am not seeing a link.

Have you tried measuring the pot to see if its value changes abnormally in that last bit?
 
Talked to the head electrician at work and his only thought was that perhaps the fan blades were bending and flattening out (thus becoming less aggressive), he didn't see any reason why the amp draw should be dropping off like that (assuming that the RPM stays the same).

Aaron Z
 
FYI: You mention a video, but I am not seeing a link.

Have you tried measuring the pot to see if its value changes abnormally in that last bit?
Fixed it. Recent transition has been messing with my YT links and pics.

We tested both pots. Only thing wrong was a very small dead spot in the higher impedance end of each one in the same location. Had no effect on the operation.
 
Talked to the head electrician at work and his only thought was that perhaps the fan blades were bending and flattening out (thus becoming less aggressive), he didn't see any reason why the amp draw should be dropping off like that (assuming that the RPM stays the same).

Aaron Z
Multi_Wing touts a strong blade that keeps its shape. I poured a little bit of water out of a cup through the fan at full speed to see if it blew in line with the air flow out outward in a radial direction. It all went radial. Maybe I can record some more videos and catch the blades bending in the stroboscopic view.

I can't think of anything else, either. The motor should be much more efficient on a PWM as it's receiving pulses of the full voltage. The 25ish amps near the top seems perfectly reasonable. Still, I slowly turn the pot higher and you can hear and see the fan RPM increase while the current draw drops off to 1.3 amps in a very linear fashion. Slowly backing the pot back down to the 25 amps results in a perfect opposite of the 1.3 amp ramping back up linearly, the fan RPM slowing a little, and the amps settle back around the high 20's.
 
Helps if you have your meters set on DC, or even a DC capable meter...

Also testing free air is not going to be helpful, power consumption on the core will be much higher.
 
Helps if you have your meters set on DC, or a DC capable meter...
That my biggest problem? My neighbor's meter had DC, but would not read on it. The clamp specified AC mA and that was the only setting I could get a reading on. Thought that was odd as I initially wanted to compare my meter to it.
 
The power it takes to spin that fan fast enough to "flatten" the blades (not likely) is sooooo much higher than 1 amp.

I missed the part about the meter and AC amps, you absolutely have to use a DC meter to measure DC amps????
AC amp reading will be useless.
 
I use something like this in my RV for DC loads and a non shunt style for AC loads. They are both so cheap they are great tools.
I thought about using a shunt to read the amps before I bought another clamp meter. Didn't feel like ordering all the parts to assemble that. Guess I'll order one (not from Amazon).

Not sure why my neighbor's meter wouldn't read any amps on any setting other than the AC mA setting. I has the same settings in AC and DC, but would only show 0.00 in DC no matter what I did.
 
Use light bulbs or known loads to calibrate the meter.

Are you measuring pre PWM driver or after?
 
Use light bulbs or known loads to calibrate the meter.

Are you measuring pre PWM driver or after?
Measuring pre in the video. I tried pre and post a few times each to make sure I was seeing things right. Now that I'm thinking about shunts, I remember that I still need to get one for the main battery bank. Could go ahead and get one appropriate for both the bank and testing this motor setup.
 
You aren't using Victron I think but they came out with a smart shunt that is wireless, seems cool for my uses.
 
You aren't using Victron I think but they came out with a smart shunt that is wireless, seems cool for my uses.
Badassery. I had seen something about their smart shunt not long ago, but never looked into it. Just watched their explanation video. Looks like I can just hook it up and connect the bluetooth to get my readings in -Amps. This would be an extraordinarily hand tool.

Correct that I'm not using Victron. Schneider had some major advantages. I did recently see Victron posted something about a new inverter. I think it was something about split-phase. If they do what Schneider did, I'll switch to Victron. Lots of highly innovative stuff coming from them.
 
That Kobalt meter shown is useless on DC current. I can't see what you have the other meter hooked to but it by itself is also useless in this case. If you have it hooked to a current probe most I have seen will be sending DC voltage out, so you should have the meter on that. About 50% of those fluke etc clamp probes for use with meters are AC only as well so check its spec.

Shunt works well as a cheap way to measure, will be usually something like 1 mV / A range. Best to use with a scope vs a meter. You can also loop the wire through a clamp meter more than once to get better resolution if the scales do not work in the range you want.

With the PWM driver you should have a scope to be checking all these things. Then you can see the frequency and duty cycle output you have. Current on any of the other meters will be an average, which might be wrongly based on 60Hz assumptions unless you have a true RMS meter. Then it still is only giving you RMS current vs the waveform of the current.
 
Badassery. I had seen something about their smart shunt not long ago, but never looked into it. Just watched their explanation video. Looks like I can just hook it up and connect the bluetooth to get my readings in -Amps. This would be an extraordinarily hand tool.

Correct that I'm not using Victron. Schneider had some major advantages. I did recently see Victron posted something about a new inverter. I think it was something about split-phase. If they do what Schneider did, I'll switch to Victron. Lots of highly innovative stuff coming from them.
Yeah and they are open source in the software side so you can write your own displays etc. (I am not that advanced yet but I can dream).
 
That Kobalt meter shown is useless on DC current. I can't see what you have the other meter hooked to but it by itself is also useless in this case. If you have it hooked to a current probe most I have seen will be sending DC voltage out, so you should have the meter on that. About 50% of those fluke etc clamp probes for use with meters are AC only as well so check its spec.

Shunt works well as a cheap way to measure, will be usually something like 1 mV / A range. Best to use with a scope vs a meter. You can also loop the wire through a clamp meter more than once to get better resolution if the scales do not work in the range you want.

With the PWM driver you should have a scope to be checking all these things. Then you can see the frequency and duty cycle output you have. Current on any of the other meters will be an average, which might be wrongly based on 60Hz assumptions unless you have a true RMS meter. Then it still is only giving you RMS current vs the waveform of the current.
Other than the Kobalt being of no use on DC current, it's much more sensitive and faster than any other cheap meter I've had. The other meter is shown switched to AC mA. It say Aac on the left range and Adc on the right. I was under the impression my neighbor had been using it on DC circuits at work, so it would've been calibrated. Maybe not.

I used to have an older o-scope. Seems to have disappeared in the last two or three moves we've made, like a lot of other items I could use right now. The controller manual states and internal freq. of 1.6kH, which, as you mentioned, could be throwing the AC clamps way off due to their calibration to use 60hz.

I'm still convinced that the motor is using much less current overall. At full tilt and several minutes' run time, the transistors barely warm to the the touch and the cable lugs barely warm at all. I should whip out my IR temp gun to get actual numbers.
 
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Slapped a new battery in my tach. Steady 1,400RPM at the peak (incorrect) amps and 1,800 at top speed.
 
I use a Snap-On Vantage Graphing meter (the old/original version). It's bad ass for automotive type repair.
I keep looking at the chi-com graphing meters because Fluke 123 is too much $.

Something like this is what I am looking at going too.
 
I use a Snap-On Vantage Graphing meter (the old/original version). It's bad ass for automotive type repair.
I keep looking at the chi-com graphing meters because Fluke 123 is too much $.

Something like this is what I am looking at going too.
I could go with that. Passed on a lot of stuff that I needed a scope for. I've been pining over Fluke meters for years. Every time I've been in the need for a meter, I've only had a fraction of the money that it takes to buy a Fluke.

The Victron app has a crap load of parameter that would be very useful for most everything I mess with. The graph might even catch the starting amps if I connect the motor direct again. I've been basing the SoC off how long my Battery Tender Junior 800 is doing. With the PWN controller in the equation, that batteries take very little to top off. The adjustable soft start in the controller is a huge help, too.
 
Other than the Kobalt being of no use on DC current, it's much more sensitive and faster than any other cheap meter I've had. The other meter is shown switched to AC mA. It say Aac on the left range and Adc on the right. I was under the impression my neighbor had been using it on DC circuits at work, so it would've been calibrated.

Measuring current using only that multi meter it would need to be in series in the circuit, your maximum value there is 10 amps if you use the right range and lead placement on the meter. My experience is the 10 amp fuse comes back blown on those meters 9/10 times when you let someone else use yours.
 
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Measuring current using only that multi meter it would need to be in series in the circuit, your maximum value there is 10 amps if you use the right range and lead placement on the meter. My experience is the 10 amp fuse comes back blown on those meters 9/10 times when you let someone else use yours.
Been there. At least there's a fuse lol.

I think I'll grab the 500 amp Victron smart shunt as soon as I have the funds. The solar retailers are starting to send out their Earth Day discount emails. Seems like the most painless and effective way to go on this. It'll bolt right into what I have hooked up, too.

Ordered two larger fans for this that shipped out this morning, so I'll really need the ability to keep a close eye on the current draw with accuracy. Don't want to smoke one system in an attempt to keep another cool.
 
That Kobalt meter shown is useless on DC current. I can't see what you have the other meter hooked to but it by itself is also useless in this case. If you have it hooked to a current probe most I have seen will be sending DC voltage out, so you should have the meter on that. About 50% of those fluke etc clamp probes for use with meters are AC only as well so check its spec.

Shunt works well as a cheap way to measure, will be usually something like 1 mV / A range. Best to use with a scope vs a meter. You can also loop the wire through a clamp meter more than once to get better resolution if the scales do not work in the range you want.

With the PWM driver you should have a scope to be checking all these things. Then you can see the frequency and duty cycle output you have. Current on any of the other meters will be an average, which might be wrongly based on 60Hz assumptions unless you have a true RMS meter. Then it still is only giving you RMS current vs the waveform of the current.

I'd bet on something like this as well.

Just going on theoretical...the amp draw from the battery when used on a PWM will be a series of square waves. To an inductive meter set to AC you could have something picked up depending on the meter sensitivity that would 'look' sort of like AC, but bouncing between + and 0 rather than +/- (loosely referring to direction of current flow). So likely a crap number anyway. Above a certain threshold it probably exceeds the sensitivity of the meter and just starts looking like noisy DC which is why the meter drops off.
 
I'd bet on something like this as well.

Just going on theoretical...the amp draw from the battery when used on a PWM will be a series of square waves. To an inductive meter set to AC you could have something picked up depending on the meter sensitivity that would 'look' sort of like AC, but bouncing between + and 0 rather than +/- (loosely referring to direction of current flow). So likely a crap number anyway. Above a certain threshold it probably exceeds the sensitivity of the meter and just starts looking like noisy DC which is why the meter drops off.
This probably nails it. I'll have the funds to get the shunt by next Sunday, if not earlier. So probably two weeks by the time I have it in hand. Slow going, but that'll give me some time to figure out what I'm mounting the other fans to the motor with.
 
Ordered the shunt on April 22nd and received it today. I know Victron and Dragonfly Energy work together a lot. Might be why the shunt fits completely perfectly on a Battleborn battery.

I had the app on my phone. Should be able to test this out tonight or tomorrow. I'm curious to see what all I can do with this thing. Updates will be made.
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Their use of "minus" and not "negative" or "ground" bothers me for some reason.
 
Their use of "minus" and not "negative" or "ground" bothers me for some reason.
Yeah really. Victron is Swedish or something. Maybe "minus" is the most common for them. Still works.

Edit: Looked them up again. Victron is from the Netherlands.
 
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that thing is super neato.

If anyone needs a cheaper option, I've used this one for a lot more than just rc airplanes.
it's accurate enough, I've used it to 125 amps and it didn't let the magic smoke out.
 
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