Hydraulic Solenoid Valve coil voltage problem

DSGarcia · Jan 11, 2008

I have some I/O blocks that are designed to switch 24VDC. I have a customer with 12VDC hydraulic solenoid valve coils. Can I use a resistor in series with my outputs to drive the 12V coils with my 24V power supply? If so, how do I calculate the resistor value required for the coil?

Notes:
I don't know manufacturer/model number at this time, but I can eventually get it if this would work.

I can't change to 24V coils because they have some legacy controls that they would like to keep in place (I will protect outputs of all equipment with diodes). Only one system at a time would be controling the equipment.

The I/O blocks I am using only work with 24VDC. They are sealed units with connectors (IP67) so external relays are not a solution here.

Thanks,
Dale

k7elp60 · Jan 11, 2008

If you can measure the coil resistance of the 12V solenoid coils with a DMM you can use the same value of resistor or one that is close, connected in series with the 12 solenoid to work on 24V. The wattage of the resistor will depend upon the current flow. If you post the resistance there are forum members that can help you calculate the wattage for the resistors.

DSGarcia · Jan 11, 2008

K7elp60,
Thanks. My main question was if I could/should do it. It appears that you think that it is OK.

With a coil, I didn't think I could directly measure the resistance. My thought was to measure the current while the coil were energized, then calculate the resistance based on current flow and voltage (or get the wattage specification from the manufacturer once I find out the mfg. model number and then calculate current and resistance).

From there I can calculate wattage, but I will oversize (derate) the resistors to allow for a higher ambient temperature (worst case is in a closed box in the summer). Each coil will only fire about 5 seconds per minute.

Does that sound reasonable (i.e., do all the normal calculations hold true with an inductive load)?

Thanks,
Dale

Roff · Jan 11, 2008

Ohmmeters measure resistance exactly as you are proposing to do it. The inductance only changes how long the current takes to reach final value.
The solenoid will switch (reach final current value) faster with 24V, because the L/R time constant gets cut in half when you add a series resistor equal to the resistance of the solenoid.

Leftyretro · Jan 11, 2008

DSGarcia said:
K7elp60,
Thanks. My main question was if I could/should do it. It appears that you think that it is OK.

With a coil, I didn't think I could directly measure the resistance. My thought was to measure the current while the coil were energized, then calculate the resistance based on current flow and voltage (or get the wattage specification from the manufacturer once I find out the mfg. model number and then calculate current and resistance).

From there I can calculate wattage, but I will oversize (derate) the resistors to allow for a higher ambient temperature (worst case is in a closed box in the summer). Each coil will only fire about 5 seconds per minute.

Does that sound reasonable (i.e., do all the normal calculations hold true with an inductive load)?

Thanks,
Dale

That plan should work fine. Lets say the 12v solenoid draws 1 amp. That would represent a 12 ohm load. If you added a 12 ohm resistor is series with the solenoid wired to 24v, then the solenoid would draw the same one amp.

However the 12 ohm 'dropping' resistor would disspate 12 watts of power and have to be size to say 20 or higher watts depending on where and how it's mounted.

Do first find out the current requirements of the 12v solenoid, the rest should be easy.

Lefty

DSGarcia · Jan 12, 2008

Thanks everyone. I wasn't sure how inductive loads affected the calculations and solution. My plan is to find out the manufacturer and model number. Their specification would be given as voltage and wattage and then I can calculate the rest. However, when I had someone go and look at the solenoid coils, there were no visible markings. I will try to get the information from the other vendor.
Thanks,
Dale

k7elp60 · Jan 12, 2008

DSGarcia said:
K7elp60,
Thanks. My main question was if I could/should do it. It appears that you think that it is OK.

From there I can calculate wattage, but I will oversize (derate) the resistors to allow for a higher ambient temperature (worst case is in a closed box in the summer). Each coil will only fire about 5 seconds per minute.

Does that sound reasonable (i.e., do all the normal calculations hold true with an inductive load)?

Thanks,
Dale

Since the coils will only be energized for 5 seconds the resistors normally would not need to be oversize. In fact they could be undersize, but I think this is a judgement call.
As a side note I just did as recommended. Have a 12V relay. Measured resistance of coil....110 ohms. Put 120 ohm resistor in series, relay energized on 24 volts with very close to same current draw on 12V.

Roff · Jan 12, 2008

DSGarcia said:
Thanks everyone. I wasn't sure how inductive loads affected the calculations and solution. My plan is to find out the manufacturer and model number. Their specification would be given as voltage and wattage and then I can calculate the rest. However, when I had someone go and look at the solenoid coils, there were no visible markings. I will try to get the information from the other vendor.
Thanks,
Dale

You gave the impression that you have an ohmmeter. That and some arithmetic are all you need.

SixBullets · Jan 12, 2008

Series resistance wrong Idea!!

Hello every one, adding series resistance is a wrong plan as it delays the valve actuation time and also wattage of the resistance needed will be large.
for any inductive load voltage is not that critical as is the current

so adding additional circuit (PWM control) to control the current in the valve is the best solution.

Roff · Jan 12, 2008

SixBullets said:
Hello every one, adding series resistance is a wrong plan as it delays the valve actuation time<snip>

That is wrong. As I said in my previous post, adding a series resistor, along with doubling the supply voltage, actually speeds up valve actuation time, because it reduces the L/R time constant. The simulation below (in LTspice) illustrates this.

ljcox · Jan 12, 2008

SixBullets said:
Hello every one, adding series resistance is a wrong plan as it delays the valve actuation time and also wattage of the resistance needed will be large. This is wrong, as Roff showed in his post. The time constant is L/R.
for any inductive load voltage is not that critical as is the current
so adding additional circuit (PWM control) to control the current in the valve is the best solution.

I would not use the PWM solution since the soleniod is designed to operate with a 12 Volt supply, if you apply 24 V pulses, it will reduce the operating life since the solenoid will move faster and hit the stop harder.

Roff · Jan 12, 2008

ljcox said:
I would not use the PWM solution since the soleniod is designed to operate with a 12 Volt supply, if you apply 24 V pulses, it will reduce the operating life since the solenoid will move faster and hit the stop harder.

You could PWM it with a period much shorter than the time constant of the solenoid, but it seems to me like that might slow it down somewhat. With the OP's low duty cycle (5 sec/min), a resistor seems like the simplest solution to me.

SixBullets · Jan 13, 2008

Hi Roff,
your analysis is correct.

Hi ljcox,
only limiting factor for selecting the voltage will be coil insulation.
solenoid hitting harder can be controlled by PWM.

I will never go for series resistance even if it is simpler(not permanent) solution as the latching and holding current are different for solenoid. And also the additional load on the supply.

ljcox · Jan 13, 2008

SixBullets said:
Hi Roff,
your analysis is correct.

Hi ljcox,
only limiting factor for selecting the voltage will be coil insulation.
solenoid hitting harder can be controlled by PWM.

I will never go for series resistance even if it is simpler(not permanent) solution as the latching and holding current are different for solenoid. And also the additional load on the supply.

Are you saying that the PWM pulses would be tapered, ie. short at the start and gradually increased in width?

If so, it should work if there is a diode across the solenoid as the current would be a type of sawtooth waveform with a gradually increasing average.

Roff · Jan 13, 2008

I not sure what he meant, but here's a sim of the solenoid running of 12V, and the same one PWM'ed at 50% on 24V. Looks OK to me. But I'm no solenoid expert.
I included the schematic of compb (behavioral comparator), in case anyone wonders what it is. I just used it as a quick and dirty PWM gate, or modulator, or whatever the hell you want to call it.

DSGarcia · Jan 15, 2008

The PWM is getting a little beyond me. Let me make a few additional comments if it will help identify the proper solution.

A slight delay in the time to energize and de-energize the solenoid is not a problem. They operate hydraulic cylinders and I can live with as much as 150ms of slop.

There is no problem with 25 watt resistors. However, I noticed you can purchase inductive and non-inductive resistors. If I use the resistors, which version do I need?

The power supply is a 100 Watt industrial power supply. Usually, only one solenoid will be firing at a time, but it is possible to have as many as two at once. On average, there will be no more than (4) 3-second firings per minute among 12 solenoids and no more than (2) firings per minute on any one solenoid.

The components must be able to withstand being in a metal box in the summer (in the shade) and must be reliable.

I would like to use the resistor solution, but if the PWM is the correct solution, then I would need a complete circuit (because it would be a little bit beyond me to design such a circuit).

Thanks,
Dale

Roff · Jan 15, 2008

You really need the specs on the solenoids.

rjvh · Jan 15, 2008

just an idea to test out
use a 7812
output from the device in the input of the 7812
output from the 7812 to the solenoid
other wire from the solenoid to the - terminal of the 7812 and device
might work

ljcox · Jan 16, 2008

Roff said:
I not sure what he meant, but here's a sim of the solenoid running of 12V, and the same one PWM'ed at 50% on 24V. Looks OK to me. But I'm no solenoid expert.
I included the schematic of compb (behavioral comparator), in case anyone wonders what it is. I just used it as a quick and dirty PWM gate, or modulator, or whatever the hell you want to call it.

Ron,
To whom does the "he" refer? Did you mean me or "six bullets"?

k7elp60 · Jan 16, 2008

DSGarcia said:
There is no problem with 25 watt resistors. However, I noticed you can purchase inductive and non-inductive resistors. If I use the resistors, which version do I need?

The power supply is a 100 Watt industrial power supply. Usually, only one solenoid will be firing at a time, but it is possible to have as many as two at once. On average, there will be no more than (4) 3-second firings per minute among 12 solenoids and no more than (2) firings per minute on any one solenoid.

Thanks,
Dale

I still think your best solution is with resistors. You could use either as the inductance of the inductive riesotors is a fraction of the inductance of the solenoid because the resistor is made from a highly resistive wire like nichrome, whereas the solenoids are most likely wound with copper wire. If vibration is a problem because of the solid wire on the resistors, there are resistors that have solder terminals and mounting flanges so you could use stranded wire for the connections.

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Hydraulic Solenoid Valve coil voltage problem

New Member

Active Member

New Member

Well-Known Member

New Member

New Member

Active Member

Well-Known Member

New Member

Well-Known Member

Attachments

Well-Known Member

Well-Known Member

New Member

Well-Known Member

Well-Known Member

Attachments

New Member

Well-Known Member

New Member

Well-Known Member

Active Member

Similar threads

New Articles From Microcontroller Tips