DC motor current draw

[JNHEscher]

that thing is super neato.

If anyone needs a cheaper option, I've used this one for a lot more than just rc airplanes.

GT Power 180A Watt Meter and Power Analyzer [GTP180AWM] Motion RC

180A Watt Meter and Power Analyzer from GT Power - GTP180AWM The GT Power 180A Power Analyzer with backlit display is a "must have" diagnostic tool for the RC enthusiast. This self-powered device allows you to measure power and energy consumption of any device with a battery. Use it to ensure...

www.motionrc.com

it's accurate enough, I've used it to 125 amps and it didn't let the magic smoke out.

That thing's pretty rad, too. As stupid as it seemed to make this thread, it has reinforced my thought to make a few threads that cover every useful tool of the same ilk in one place so we all have a quick resource for stuff like this.

 

[JNHEscher]

That's more like it. First dip is a gradual rpm increase. Second dip is with the soft start pot turned all the way down and speed pot instant full to graph the inrush current.

I'm going give this several test runs. The PWM controllers are rated for 60 amps with a 200% overload for 10 seconds and 150% overload for 60 seconds. The motor is rated for 55-65 amps. Full speed with the 22" fan looks to sit around 74 amps. I'll take note of what rpm I can get at 60 amps running.

 

[JNHEscher]

10-minute scale. 1,700 rpm at around 65 amps, 1,750 rpm at full which appears to settle around 70 amps. Hottest component was the motor commutator at a steady 156 deg. Next hottest was the controller input/output wire terminal plates at 86 deg. Everything else sat at 71 deg.

I'll mess around with the app to see if I can dial in the amps scale. Right now, the spread is a little funky for eyeballing an exact amperage.

Full pull didn't phase any part of the whole setup. Safe to say that I can run the larger fans at a lesser pitch and lower rpm. The 22" fan blows hella hard.


Hat's off to CarterKraft for once again leading me in a most excellent direction. I'll keep testing this and post up any worthwhile updates.

 

[CarterKraft]

Right on.

I love my Victron gear and I think you will find it very useful going forward.

 

[2020AT4]

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?

At the higher speeds your fan blades stall as they can’t get enough air.

I are an RC heli pilot and this is something you deal with in flight regularly.

 

[2020AT4]

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.

Dollars to doughnuts you are hearing a marked difference in sound between the two too.

The water is going to do centrifugal stuff regardless. If the fan were moving through the air at speed, then you would see it going with the airflow.

 

[JNHEscher]

At the higher speeds your fan blades stall as they can’t get enough air.

I are an RC heli pilot and this is something you deal with in flight regularly.

I still suspect that this happens somewhere in there. For the most part, I'm thinking it is now a moot point. My motor is spinning the 22" fan at half the rated fan speed which still puts out some great pressure. Slightly different story when this gets mounted as a radiator fan, but should be sufficient regardless.

The graphs are succinct and all components manage quite well. I ran a 15-minute test at full speed yesterday and got no more than 91 deg in the controller and 164 deg on the commutator bars.

The larger pair of fans that I got are all aluminum. The thought to copy parts in carbon fiber keep crossing my mind because the alu is too heavy.

 

[87manche]

I still suspect that this happens somewhere in there. For the most part, I'm thinking it is now a moot point. My motor is spinning the 22" fan at half the rated fan speed which still puts out some great pressure. Slightly different story when this gets mounted as a radiator fan, but should be sufficient regardless.

The graphs are succinct and all components manage quite well. I ran a 15-minute test at full speed yesterday and got no more than 91 deg in the controller and 164 deg on the commutator bars.

The larger pair of fans that I got are all aluminum. The thought to copy parts in carbon fiber keep crossing my mind because the alu is too heavy.

brother your'e getting into real sketchy loads with fan blades at those RPMs.

I wouldn't trust home made carbon fiber fan blades.
and i've made a significant amount of things from composites.
even have my own vacuum bagging setup in the basement.

I would leave it as is with the plastic ones and see if they're up to the job.
revisit if they aren't.

 

[JNHEscher]

brother your'e getting into real sketchy loads with fan blades at those RPMs.

I wouldn't trust home made carbon fiber fan blades.
and i've made a significant amount of things from composites.
even have my own vacuum bagging setup in the basement.

I would leave it as is with the plastic ones and see if they're up to the job.
revisit if they aren't.

Larger fans at much lower rpm. I don't want to spin 28" fans at 1,800 rpm. The nylon 22" fan is nuts as it is. I have to call Multi-Wing to see if I can get a part number for their sickle blade nylon equivalent. They're current something like 21 pounds each. Got the type 5 adjustable pitch hub with 9 blades.

Basically, this whole test is for running every component to the max to see if they hold up so that I know the limit and that the end result of the installed system is well within spec. Running great. I feel much more comfortable with it now. Screenshot below is of me adjusting the speed pot to spin the fan at 900 rpm. 10.5ish amps and still lots of air.

 

[87manche]

I honestly wouldn't worry about the assembled weight unless you have some sort of bearing issue that precludes it standing up to the loads of gyroscopic forces.
once the mass is spinning it's spinning.
your initial load might be more, but I'd bet the running wattage with a lighter fan at the same pitch is so close that it's damned near immeasurable.

having played plenty with lighter/heavier props. i've run heavy props on electric motors and the current doesn't go up, but the little electric motor bearings fail because of the forces involved when you change the direction of the aircraft.

edit:
I'm also talking about 10K+ rpms and very abrupt angular momentum changes to the prop.
at your fan speeds and such I really don't think it's even a problem worth worrying about, as long as the fan performs well enough to cool your junk.

 

[CarterKraft]

The only issue I see is you are going to be dumping whatever BTU your cooler can handle into your fan motor.
It would seem the fan motor would end up being coolant temp after running for a hour or so.

 

[JNHEscher]

I honestly wouldn't worry about the assembled weight unless you have some sort of bearing issue that precludes it standing up to the loads of gyroscopic forces.
once the mass is spinning it's spinning.
your initial load might be more, but I'd bet the running wattage with a lighter fan at the same pitch is so close that it's damned near immeasurable.

having played plenty with lighter/heavier props. i've run heavy props on electric motors and the current doesn't go up, but the little electric motor bearings fail because of the forces involved when you change the direction of the aircraft.

edit:
I'm also talking about 10K+ rpms and very abrupt angular momentum changes to the prop.
at your fan speeds and such I really don't think it's even a problem worth worrying about, as long as the fan performs well enough to cool your junk.

I highly appreciate this knowledge. Makes a lot of sense. The controllers have a very nice soft-start adjustment that will likely help with spinning up more weight. The larger fans are too much to be hanging off the ball bearings that hold the motor armature. With that, I'm going to figure out shafts and pillow blocks for the fans to mount to. I just need to buy or make different mounting adapters for the fan hubs. They're currently some oddball ID with a very slight, keyed taper. No idea what shaft they were made to fit.

The only issue I see is you are going to be dumping whatever BTU your cooler can handle into your fan motor.
It would seem the fan motor would end up being coolant temp after running for a hour or so.

I think we were talking about this in the original thread. The motors will get mounted pre-radiator so that the coolest air passes over the motors first. They'll certainly get a bit hotter than what I've been measuring in the living room because they will be mounted in a more enclosed location. Probably seeing more air velocity in their permanent home, though. The batteries are topping off now. I'll be giving this a 30-minute, full-speed run and more unless I see that to be satisfactory.




Looks to me like this can be continued back in the engine bay thread. Great success, thanks to all. Some of the comments in the slow start of fan thread helped, too. Next hurdle is mounting those damn cores.

 

[aczlan]

Might want to use tapered roller bearings rather than ball bearings(at least for the side away from the radiator in a pusher configuration) unless the ball bearings are rated for a the thrust load of the fan pushing air through the radiator.

Aaron Z

 

[JNHEscher]

Might want to use tapered roller bearings rather than ball bearings(at least for the side away from the radiator in a pusher configuration) unless the ball bearings are rated for a the thrust load of the fan pushing air through the radiator.

Aaron Z

I'd have to get sealed bearings for the motors. Rollers can definitely be done if I can find a way to seal them. Probably best to go for a dedicated shaft on pillow blocks because these fans aren't really balanced that well. Too much weight and too big of a swing to mount directly on a 3/4" motor shaft. Tapered roller pillow blocks are pricey. I wouldn't mind if ball bearing pillow blocks wore out quicker than everything else. They're cheap and easy to replace.

 

[aczlan]

Why are they too big? Space constraints in the area they are going?
We have hundreds of large cast aluminum fans (not sure on size, some are at least 24") on 1.5-3HP motors at work in a pull configuration as well as a few 36" (ish) fans that appear to have carbon fiber blades in a push configuration.

Aaron Z

 

[JNHEscher]

Why are they too big? Space constraints in the area they are going?
We have hundreds of large cast aluminum fans (not sure on size, some are at least 24") on 1.5-3HP motors at work in a pull configuration as well as a few 36" (ish) fans that appear to have carbon fiber blades in a push configuration.

Aaron Z

What size shafts are they on?

The bigger fans are 28.5" diameter. All cast aluminum hubs and blades unless I get the nylon blades.

The motor should spin it. They're just more centrifugal weight than I would care to hang on a 3/4" shaft. Going in a mobile application, they'll get bounced around and vibrated along with all the vibration that will come from the fan spinning. 3/4" shaft is too weak to handle all that, if you ask me. Can't get any great pics at the moment. Only propped it against the 22" fan for a perspective.

I'm supposed to be getting a quote email from Multi-Wing about mounting hubs. I didn't ask, but I'm not sure they offer a hub to fit 3/4" on something this large.

 

[aczlan]

They are a larger shaft on some of them, I think the one we replaced last week (stress fracture in the blade) was a 1 1/8" shaft.
That was on a 2HP 1165RPM 3 phase 480V motor.
I suppose you could install a overhung load adapter like this: Zero-Max Model 210 Overhung Load Adapter for 1 Keyed Shaft Input SAE A 2 bolt mount | Overhung Load Adapters | Hydraulic Pump Mounts | Hydraulics | www.surpluscenter.com
Then you would just need a step up shaft adapter to go from 3/4" to 1".
Could probably buy a lot of 1 1/8" pillow block bearings for that price though.

Aaron Z

 

[JNHEscher]

Yeah, I looked at the overhung adapters. Too costly compared to shaft and pillow blocks to do about the same thing.

 

[87manche]

balance the fans after assembly.

if you want to be super fancy, put some different colored marks at the tips and tip track them as well.

for maximum quietness and performance.

all you need to balance them is a low drag shaft that they fit on.

 

[JNHEscher]

balance the fans after assembly.

if you want to be super fancy, put some different colored marks at the tips and tip track them as well.

for maximum quietness and performance.

all you need to balance them is a low drag shaft that they fit on.

Radial balance is easily done. I'm not sure about the axial wobble. The 22" fan has some decent wobble. Comes from both the blades and the clamshell hub. The 28" fans look about the same.

Gotta check with Multi-Wing to see if the quote email got sent. Would like to get these fans on a shaft.

 

[87manche]

the axial wobble may just be blade path issues.

tip tracking them will get them all to run in the same plane. They're adjustable, so tiny adjustments at the root pitch angle make big adjustments at the tip for blade tracking when they flatten and flex.

a model incidence meter may be useful to you in setting all of the blade angles precisely to start.
i've owned one of these forever, and my dad's is probably 40 years old at this point.
jeweled incidence meter.

Robart Manufacturing Model Incidence Meter | Horizon Hobby

The Model Incidence Meter by Robart Manufacturing is a quality built remote controlled airplane accessory. See all our RC product options online at Horizon Hobby!

www.horizonhobby.com

i've never tried it on anything curved though, so not sure how you're manage that.

 

[Satan's_Minion]

A LOT of horrible advise in this thread.

My suggestion, do not spend another dime on this until you can test with the shroud behind the core you want to use. Power consumption will be increased significantly by the restriction.

Your testing on battery voltage will be lower resulting speed/power than you will see with alternator 28 volt input.

Also do not assume that the motor can run at any RPM you want maximum rated power. If the average current is at nameplate running on reduced % duty cycle you are putting more than that into the motor during the on time.

This maximum power will be considering some assumed working air temperature also. My knowledge of those HVAC applications would be in the 140-150F range. At lower flow you may exceed this temp, and also consider heat soak etc.

 

[87manche]

I just know about props man.
:Flipoff2:

But you're right that all of this will change after installation. I only mess with brushless motors in free air.

 

[JNHEscher]

My suggestion, do no spend another dime on this until you can test with the shroud behind the core you want to use. Power consumption will be increased significantly by the restriction.

That's up next. All this is taking me forever with waiting for parts orders, funds, weather, etc.

 

[JNHEscher]

A LOT of horrible advise in this thread.

My suggestion, do not spend another dime on this until you can test with the shroud behind the core you want to use. Power consumption will be increased significantly by the restriction.

Your testing on battery voltage will be lower resulting speed/power than you will see with alternator 28 volt input.

Also do not assume that the motor can run at any RPM you want maximum rated power. If the average current is at nameplate running on reduced % duty cycle you are putting more than that into the motor during the on time.

This maximum power will be considering some assumed working air temperature also. My knowledge of those HVAC applications would be in the 140-150F range. At lower flow you may exceed this temp, and also consider heat soak etc.

Ran out of time this morning.

I'm hoping to order parts to assemble the radiator cores shortly. The assembly will still take a while.

I did see that the bench testing setup was in the 25-26.25 volt range. The bus regulator is set at 27.5 volts and likely to be bumped up the 29 volts for the lithium. This will obviously make a change to efficiency and current draw. Finding out soon enough. The controllers have min and max rpm pots, so even with the input it will receive, it'll hold speeds within range.

These motors state a 100% duty cycle at 65 amps. Not sure I understood entirely what you were getting at. These motors are for the OTR air conditioning condenser fans that run constantly in coach buses. I can imagine that a bus with 50+ people in it takes some serious power to keep cool.

In HVAC, you see 140-150 deg air between a fan and a condenser or evaporator coil? I know that compressing air heats it up and that radiators rely on air pressure. I might be able to set this up as pullers. Depends on whether or not I can transmit the power from one side of the cores to the other. Pushers should still be just fine and I could easily set up a low pressure gauge to see what these fans actually push once their in a shroud and pushing against the cores.

 

[Satan's_Minion]

Voltage = speed for brushed motors. It does not overly effect the efficiency within the range we are talking about.

If you are adjusting the speed with a PWM you are doing so by not powering the motor for some % of the time. Your current measurement and is an average based on 100% of the time, but if you look at a waveform of the current during the on time it would be higher than your measured value.

Temp rise would be from the heat exchanger, there is no perceivable increase due to the pressure rise, which is in the range of 0.1 PSI max. You will also see a bit of recirculation increasing the temp. Assume your starting working temp is in the 120 range off the pavement. Pusher setup might not be too much above that but on the hot side of the core would be 30-40 degrees rise.

 

[JNHEscher]

I'm well aware that voltage equals speed on brushed motors. Higher voltage might increase the efficiency of the PWM controller. Might, but I don't know yet. Dart Controls doesn't mention so, but I've read so on a few other PWM controllers. I still need to read the voltage at the motor terminals. It's probably lower than what the controller receives from the batteries.

I just got funds today to place a bus parts orders. One item is a DC breaker that I want to hook up to the test setup so I can quit arcing the post when I connect the lug. I plan to bypass the PWM controller and measure the current with a (mostly) direct connection between the motor and batteries because the test I did before showed higher RPM that way and the shunt will give me the correct reading this time. I'll get an idea of what the actual current draw is and post up the graph. Getting closer.

Can't say that I care too much about the fan temp. I thought you were saying that they heat up to 14-150 pushing on HVAC cores. Couldn't imagine how lol. Pusher would help the motor cooling some. The shroud narrows the path in which the air flows and the motor will sit right in the center of that path.

Suppose I'll have to paste the link to this thread into my other. This one is delving even further into the discussion. As seen, there has been a lot of talk on the aerodynamic side of the cooling. Good to discuss the electrical side in more detail.