Can the HB-25 motor controller handle this?

bulkhead

www.allelectronics.com/cgi-bin/item/DCM-171/400400/12VDC_GEARHEAD_MOTOR_.html

The description says it draws only 4 amps, but that's with no load. Is there any way to tell by the given information, whether or not the motor is too powerful for the HB-25? Or would I actually have to get a motor and hook it up for my application, then check the current?

Also, it says that it has over voltage, current, and temp protection. Does this mean it's not possible to damage it by these three methods? So if I were to hook up that motor to the controller, it would shut off automatically if the current draw were too much for it?

Post Edited (bulkhead) : 2/22/2006 5:48:08 AM GMT

Beau Schwabe

I'm not sure what the Stall current is for these motors, but I can say that I have used this exact motor before with only a 10Amp
overhead without any problems. With the 25 Amp overhead the HB-25 is capable of you should be fine. You could always go to
an automotive shop "Pep Boys", "Auto Zone", etc. and look for this exact windshield wiper motor. There should be an indication
as to what the Current rating is on the box, or you could probably measure the resistance across the terminals without too many
raised eyebrows. Tell them you are using it for something other than what it was originally designed for and you just want to test
something first before you buy.

(Current in Amps) = 12V / (Coil Resistance in Ohms)

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Tiger

Bulkhead - There is no possibility that you are going to burn up the HB-25 with that motor. In fact, you could put a couple of those in parallal and you still couldn't burn it up! If you hooked up four or five of those in parallel you "might" be able to get the HB to shutdown from heat or overcurrent. All that would do is turn on the red error light and it would quit responding until you reset it with a neutral command or remove power.

Tiger (HB-25 designer)

bulkhead

Ok, thanks for the replies. I'm just kind of confused on how all these circuits are rated. It seems like there is really no telling just by looking at the numbers? I had an RC speed control that claimed 320 Amp max forward current, which, at 7.2V, is 2100+watts, however, I ended up melting it by running it on a standard RC motor (given, the motor was geared improperly and under a huge load, but the batteries couldn't even have supplied anything near the rated 320 amps...). It's not the only hobby speed control that has such high current ratings. Anyways, what you describe about the HB-25 sounds promising, I may give it a shot.

Beau, can you really estimate stall current draw of a motor by checking the resistance across the motor's terminals? Is this an accurate indicator? Sounds interesting, I'll have to try it.

Oh, by the way, is that a heat sink or cooling fan on the HB-25? It's kind of hard to tell from the picture.

Tiger

Snip: "Oh, by the way, is that a heat sink or cooling fan on the HB-25? It's kind of hard to tell from the picture"

There is a pretty substantial heatsink which is force cooled by a 40mm fan.

...TIGER

Paul Baker

Quoting from http://www.scary-terry.com/wipmtr/wipmtr.htm·:

Scary Terry said...

[font=Georgia, Times New Roman, Times, serif]Current[/font][font=Georgia, Times New Roman, Times, serif].[/font][font=Georgia, Times New Roman, Times, serif] The minimum required current for the motor is 1.6 amps at 70 rpm, 0.9 amps at 41 rpm (and 4 amps if you elect to run it at 106 rpm). These current ratings are for the motor spinning with no load. As you add mechanical load, these numbers can increase dramatically, doubling or even tripling under a heavy load. (When testing for torque, I found the motor to draw close to 14 amps in a stalled condition.) This factor must be taken into account when selecting a power supply. Since the motor will only use what it needs when it comes to current, it's best to provide a source with a higher current rating than you think you might need. I would recommend a 5 amp or greater supply to handle most circumstances.[/font]

And yes checking the motor winding resistance is a good indication of stall current, this is because when a motor is spining, it creates an EMF field in reverse of the motor's winding, this has the effect of increasing the effective resistance seen by the power supply. When the motor is stalled, this back-EMF·doesn't exist, and since you are passing a DC current throught the windings, the windings don't react to the current, therefore only the resistance of the windings is coming into play. If you don't understand this explanation, don't worry, its not nessesary to understand.

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·1+1=10

Post Edited (Paul Baker) : 2/22/2006 4:50:45 PM GMT

LoopyByteloose

Thanks Paul,
I have been measuring resistances and estimating load, but I was unsure of what exactly it meant.

I think what you are saying is that figure from my multimeter gives the extreme high end of the load.

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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

Beau Schwabe

Kramer,

"I think what you are saying is that figure from my multimeter gives the extreme high end of the load."

That is correct.

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Hulk

I would appreciate some help with application advise.· The wiper motor that shows up in the link above has a running current stated at about 4 amps.· It probably has an initial surge (locked rotor current?) of 40 amps (if it behaves like other motors I've measured).· I've attached a file of my motor that shows a surge in excess of 100 amps until the armature picks up enough speed to build counter emf and drops the current to around 15 amps.· Given that I'm powering the motor with 12 volts, the power figure comes up to about 180 Watts or less than 1/4 HP.

Does my surge current of greater than the stated 35 amps (for about .040 seconds) prevent me from using the HB-25?· How will the HB-25 react if I try to drive my motor?· Will it shut down and protect itself?· I don't think it will blow the 30 amp fuse.· When you specify the "surge current" are you refering to the peak that I show in my attached file?

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Basic stamp Newbie

Post Edited (Hulk) : 3/2/2006 7:18:52 PM GMT

Chris Savage

While I haven't been able to test this first hand, my belief is that the HB-25 will fault when the current reaches over 30 amps, even if it is a brief pulse.

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Chris Savage
Parallax Tech Support
csavage@parallax.com

Beau Schwabe

Hulk,

Can you apply any ramping techniques during powerup?

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Gadgetman

Drop in a heavy-duty resistor to limit the current?

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Don't visit my new website...

Tiger

Hulk - I really doubt that you will have any problem with the HB-25 on your motor for several reasons. The controller can actually handle well over 30A on a surge. I've seen it do much more than that when I was beating it up during development. I'm not saying it's a good idea to bang it that hard, but I don't think it's going to hurt anything. From a practical standpoint, there are other things that come into play in a real application. First off, it's not likely you are really going to draw that much during startup when you take into account battery impedance, cable resistance and inductance. That's a LOT of current to draw unless you have a HUGE battery, giant wires, and stall the motor or slam it from forward to reverse instantly. The other thing is that the HB-25 is doing PWM so you can (and should) do a soft start by ramping it on. That's the kind thing to do to your motor anyway if you want it to live very long. There is no reason I can see to go from 0-100% instantly in any normal application. If you are really doing that, you need a giant relay - not a motor control. [noparse]:)[/noparse] As for what the HB-25 will do if you overload it, the red error light will come on and the h-bridge will turn off until you reset it.

So what exactly is this motor of yours and what are you actually going to be doing? You say it goes to 15A when it's running. I assume that is the full load current rating. Are you really running it at full load or is that just the spec?

TIGER

Hulk

Thanks for your responses!

Tiger, I'm encouraged by your comments.· I can only imagine the algorithm that the chip uses to sense an overload.· If it’s looking for an instantaneous current It may shut down.· If it’s just looking for heating I probably won’t have a problem.

I’ve never used PWM to control a motor so I will have to scope it to see how it reacts to my motor.· I will definitely do a soft start (that’s one of the reasons I need the control).· I’m making an electric car for my granddaughter.· If I use only relay control of on/off, it snaps her little neck.

I’ve also added some series resistance as suggested above.· You can see by the waveform attached below that even adding .1 ohm dramatically reduces the peak current.· I don’t know what effect it will have on steady state current when it’s actually running the car with the kid in it.

BTW, The waveforms I’ve posted show unloaded motor current on the bench.· The steady state shows a current about 5 amps higher than the “loaded” current that I measured in the past (with only on/off relay control).· I don’t know why, but suspect lead length or faulty connections may have dropped the current.

Once again, thanks for your comments.· I’m looking forward to adding the HB-25 and will post progress when it arrives.

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Basic stamp Newbie

Tiger

Hulk - After reading your last post and looking at that graph again, I'm having some doubts about all this. If I read this correctly, your last post says you are drawing almost 20 amps "unloaded motor current on the bench". If that's the case, how can you possibly stay below 25 amps when you are driving the car? What is the actual rating on this motor (volts, amps, HP)? This sure sounds like a lot of current for a little kids car! If that's really "no load" current, the motor must be huge. I can't imagine the current won't at least double when you're driving.

TIGER

Hulk

Tiger, I have several of the motors that came from an application where they were used to pump hydraulic fluid in a "Power Tilt/Trim" system for outboard motors. I'm sure the power/current/rpm curves are well documented somewhere, but I no longer have access to them.
I certainly agree with your concern: the rpm can go no where but down when the motor is loaded (no matter what gearing is applied). When it drops, the motor will draw more current and it looks like I would have only 5 amps to add before the HB-25 starts shutting down. I guess I will have to find a different motor in the old parts bin.
Your observation about high power for a kid's car is part of the objective. I'm gearing it for a maximum that will be advanced as she grows older, starting at about 5 mph. We are semi rural and have no side walks so I'm trying to make something she can ride in the yard. There are some some small hills that the commercial kid cars can't handle. I'm making a beefy steel frame to fit under one of those plastic kid car Jeep bodies.
From your comments, it looks like I have some freedom to experiment without fear of actually destroying the HB-25. If I explore the limits (near when it shuts itself down) and and occasionally exceed them (say 10 or 15) times will I harm the part?
BTW, I really appreciate your interaction on this subject. I know your time is valuable, but you share it generously!

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Basic stamp Newbie

Tiger

Hulk - Sounds like a fun project! I don't think you have to worrk about wrecking the HB-25. I suppose anything is possible, but I have tripped them here many times with over voltage, current, and temp and all it ever did was shut down. And I was trying to destroy it! [noparse]:)[/noparse] The only thing I ever did that wiped one out was reverse the voltage. There is no protection for that since it would be really difficult and expensive to do at these power levels. I have a procedure to detect correct polarity on the board using one of the LEDs 'BEFORE' you install the fuse. If folks take the time to do that, there should never be a problem with polarity. If they don't... I guess the just better get it right.

TIGER