# Calculating amperage draw when overpowering a solenoid

I have a solenoid rated at 28vdc nominal, 77.4 ohm, 10 watt. (from spec sheet)

Using Ohm's law, this tells me the current draw will be 0.36 amps. (V / R = I)

I want to overpower this solenoid (for good reasons, and it won't be full duty cycle), but am confused about how much amps it will require if I do this.

Let's say I run at 60vdc. With a resistance of 77.4 ohm, does this mean it will now require 0.77 amps?

60v / 77.4 ohm = 0.77 amps

This seems counter-intuititve somehow. I thought if I increased the voltage, it would require less amperage?

No, V = IR. Its a piece of wire with a resistance.

Of course it will rapidly heat up run at 46W like this.

60v / 77.4 ohm = 0.77 amps

Correct.
If anything goes wrong with your circuitry, you will burn something up.

OK, so if I increase the voltage of my power supply, I also have to increase the amps, which in turn increase the overall wattage. I think that makes sense.

Well, my solenoid is rated at 10watt for full duty cycle, but can take more when not in full duty cycle.

The tech sheet says

10% duty cycle = 100W
25% duty cycle = 40W
50% duty cycle = 20W
100% duty cycle = 10W

Maximum on time (sec) when pulsed continuously: at 100% (infinite), 50% (360), 25% (32), 10% (8)
Maximum on Time (sec) for single pulse: at 100% (infinite), 50% (470), 25% (120), 10%(100)

I'm using the solenoid to make musical notes, so it won't be on that often. I'm guessing using it even to 100W in the 10% duty cycle should be fine if I'm only hitting with it once in a while. Let's say say it hits every 2 seconds (just a quick Tak!) for many minutes - would this count has 10% duty cycle - or even less?

I want to overpower this solenoid (for good reasons, and it won't be full duty cycle),

What reasons? Could you post a link to the spec sheet?

Without knowing this, it seems that the duty cycle and max on time information is there to show what the maximum drive levels are (duty cycle and time) to keep within the thermal limits of the solenoid coil.

Here is the spec sheet.

It's for a musical application. Using it to make percussive hits.

According to Godfried-Willem Raes who's been building robotic musical instruments with solenoids for decades now, it's possible to get velocity control of the solenoids (how hard they hit to create musical expression - play soft or loud) by controlling the width of the pulse used to energize them. He recommends powering the solenoids with a power supply 2 to 5 times above their nominal voltage for this. So, you can then give very short pulses and the solenoids will energize and play softer, and longer pulses for harder hits. Essentially, you go under the full duty cycle. The problem when you use a power supply rated to the nominal rating of the solenoid is that when you shorten the pulse, they don't have a strong kick to come out. They don't get energized.

I am controlling 22 of these. I tried a power supply of 24vdc with 12.5 amps, but got very little velocity playing room. So, I now want to buy a power supply with more voltage to give me more head room to play with velocity control.

Here's a paper from Raes: Expression control in automated musical instruments Godfried-Willem Raes

http://logosfoundation.org/g_texts/expression-control.html

If anyone can help me figure out what a good power supply for this would be I would be so grateful. I want velocity control to the max, but also don't want to burn my solenoids. I have some problem understand duty cycle. Like, if I send them one pulse of variable width to energize them every once in awhile, I don't know how to calculate what duty cycle I am on. Say for example, I send them a pulse of 30 milliseconds every 2 seconds, what duty cycle would that be?

The information is helpful, but we would need to know the Coil AWG Number to know what the nominal DC voltage rating is. Do you know the Coil AWG Number?

I have some problem understand duty cycle. Like, if I send them one pulse of variable width to energize them every once in awhile, I don't know how to calculate what duty cycle I am on. Say for example, I send them a pulse of 30 milliseconds every 2 seconds, what duty cycle would that be?

That would be (0.03/2)*100 = 1.5% duty cycle (each second).

Another example using the performance table (my interpretation):

8 sec max ON time when pulsed continuously at stated watts and 10% duty cycle
Here, the total OFF time needs to be 71 seconds (minimum) over any 80 second interval.
The pulse on time can vary, but the total should not exceed 8 sec over any 80 second interval.

32 sec max ON Time for single pulse - the OFF time here should be 80-32 = 48 seconds minimum.

The coil AWG number is 31. The leads AWG number is 24.

It says the nominal DC voltage is 28vdc.

Here is the solenoid with some of the infos:

DATASHEET

This is a double posting but i think I understand where you are coming from.

The spec sheet for the solenoid gives duty cycle on the basis that you want more power from the solenoid than it is continuously rated for.

In other words if you want to double its thrust you have to double the input current (thrust being linearly related to ampere-turns). To achieve double the current you must double the voltage. BUT, when you double the voltage the windings would get "cooked" if you left that voltage on continuously, so you must only operate the solenoid for short durations, in this case a maximum of 470 seconds for a single pulse or 360 seconds for repeated pulses.

If 28 volts gives you sufficient thrust for your needs then it matters not that you are "pulsing" the solenoid off and on. The solenoids rated duty cycle remains at 100% but your actual operating duty cycle will be less than 100%

This offers some additional information on duty cycle and life:
http://www.johnsonelectric.com/~/media/Files/resouces-for-engineers/solenoids/solenoids-design-considerations.ashx
They may have more information available if you register on the site, or get in touch with an application engineer.

I've expanded the table with additional calculations. For your solenoid with coil specifications 31 AWG, 77.4 Ω and 3280 turns:

``````Duty Cycle            100%    50%    25%    10%
VDC(nom)              28.0   39.0   56.0   88.0
Amps V/R              0.36   0.50   0.72   1.14
Power (V*V)/R         10.1   19.7   40.5  100.1
Power * Duty Cycle    10.1    9.9   10.1   10.0   <-- no overheating
Max ON time (pulsed)     ∞    360     32      8
Total OFF time (pulsed)  0    360    128     80
``````

The end goal is having the largest dynamic range possible of hit strength. So that I can play soft, or loud hits (notes). With 28v, I have enough trust to activate the solenoids, and they hit pretty loudly, but it's very hard to make softer hits because when I make the pulse too short, they don't activate at all. According to Godfried's paper, the trick is to feed them 2-5 times more voltage than the nominal voltage and you can then send very short pulses for softer notes.

I'm starting to realize that perhaps the best way to change the thrust power in order to play different dynamics is not by changing the width of the pulse I send, but by changing the voltage I send to the solenoid. I could then send a nominal voltage with a normal pulse, or a higher voltage with a shorter pulse, etc... and perhaps get different thrusting powers like so.

What do you mean by "overpower" ? Are you simply using a 60vdc supply rather than 28vdc ?

If this is the case you still want .36 amp so the total resistance in the circuit must be 60/.36 = 166.67 say 167 ohms.

You already have 77.4 ohms so the external resistance must be 167 - 77.4 = 89.6 say 90 or even 100 ohms since 100 is easy to get.

If 90 ohms the current will be 60 / (90 + 77.4) = .358 amp

and the resistor power rating must be amps X amps X resistance or .358 X .358 X 90 = 11.56 watts (10 would probably be ok unless you have a very hot environment)

If 100 ohms the current will be 60 / (100 + 77.4) = .338 amp

and the resistor power rating must be amps X amps X resistance or .338 X .338 X 100 = 11.4 watts (10 would probably be ok unless you have a very hot environment)

This all presupposes by "overpower" you mean supply from higher voltage

djangojames:
The end goal is having the largest dynamic range possible of hit strength. So that I can play soft, or loud hits (notes). With 28v, I have enough trust to activate the solenoids, and they hit pretty loudly, but it's very hard to make softer hits because when I make the pulse too short, they don't activate at all. According to Godfried's paper, the trick is to feed them 2-5 times more voltage than the nominal voltage and you can then send very short pulses for softer notes.

In the paper you've provided, there's lots of references to 16-bit control ... its possible to get 16-bit PWM duty cycle control on the Arduino. If you've been using the default 8-bit duty cycle control (0-255) and there's too narrow of duty cycle range range for loud hits to soft or no hits, then using 16-bit duty cycle control (0-65535) might help.

I'm starting to realize that perhaps the best way to change the thrust power in order to play different dynamics is not by changing the width of the pulse I send, but by changing the voltage I send to the solenoid. I could then send a nominal voltage with a normal pulse, or a higher voltage with a shorter pulse, etc... and perhaps get different thrusting powers like so.

"Sounds" like a good idea. A digitally controlled or PWM controlled DC power supply. You may need to combine this with high precision duty cycle control for best results.

dlloyd:
In the paper you've provided, there's lots of references to 16-bit control ... its possible to get 16-bit PWM duty cycle control on the Arduino. If you've been using the default 8-bit duty cycle control (0-255) and there's too narrow of duty cycle range range for loud hits to soft or no hits, then using 16-bit duty cycle control (0-65535) might help.
"Sounds" like a good idea. A digitally controlled or PWM controlled DC power supply. You may need to combine this with high precision duty cycle control for best results.

Ha yes, I only tried 8bit PWM when testing. I will test again tonight and post the results.

phoxx:
What do you mean by "overpower" ? Are you simply using a 60vdc supply rather than 28vdc ?

If this is the case you still want .36 amp so the total resistance in the circuit must be 60/.36 = 166.67 say 167 ohms.

You already have 77.4 ohms so the external resistance must be 167 - 77.4 = 89.6 say 90 or even 100 ohms since 100 is easy to get.

If 90 ohms the current will be 60 / (90 + 77.4) = .358 amp

and the resistor power rating must be amps X amps X resistance or .358 X .358 X 90 = 11.56 watts (10 would probably be ok unless you have a very hot environment)

If 100 ohms the current will be 60 / (100 + 77.4) = .338 amp

and the resistor power rating must be amps X amps X resistance or .338 X .338 X 100 = 11.4 watts (10 would probably be ok unless you have a very hot environment)

This all presupposes by "overpower" you mean supply from higher voltage}

I mean increasing voltage, with would increase wattage. The spec sheet says you can use more voltage and wattage when the duty cycle is less than 100%.

OK You've got all kinds of information on this

Ya thanks guys, my head is turning in circles. Trying to organize my thoughts now with all this new info.