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Need component options to Start/Stop Pump 24VDC 15A

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Subject almost says it all. I'm looking for component options to start/stop a pump that runs on 24VDC and draws 15A. The 15A being the key (problem). Electromechanical relay and solid state relay I already know about (though I haven't found one to switch that much current yet).

What are my options?
 

MaxHeadRoom78

Well-Known Member
There are plenty of relays and contactors that will switch that kind of current or we would all be in trouble.
What are you using to switch the device?
If electronic, there is a Power Mosfet.
Or OPTO22 should have a SSR that will also do it.
TE also have a relay that is DC rated in thier PRD series, it has a magnetic arc blow out on the contacts for high current inductive DC load.
Max.
 
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Control can be either from 5V or 12V (5V directly from the microcontroller, or 12V from a relay). Guess I missed that important spec.

I was busy looking for a module, I didn't think of going discrete and using a power fet directly.

http://www.allelectronics.com/item/irfz40/n-channel-mosfet-50a-50v/1.html

I think this would suffice?

Oddly enough I haven't found a DC DC SSR that has an output >3A...yet. Still looking, though the power FET seems like a good idea.
 

alec_t

Well-Known Member
Most Helpful Member
If 15A is the pump running current draw then the start-up current draw will be much greater.
A 50A rated MOSFET is unlikely to survive long IMO. I'd go for something beefier.
 

MaxHeadRoom78

Well-Known Member
Control can be either from 5V or 12V (5V directly from the microcontroller, or 12V from a relay). Guess I missed that important spec.

I was busy looking for a module, I didn't think of going discrete and using a power fet directly.

.
There are logic level Mosfets, as to the starting current, Mosfets have a pulsed forward current rating that is typically 4x the continuous.
Max.
 

tomizett

Active Member
The word of automotive mechanical relays might be worth looking into as well, especially if you can find components specifically intended for lorries/trucks with 24V systems. Things like heater plugs and radiator fan easily draw this much current.

Of course, you may find yourself then needing a 5V coil relay to drive a main relay having a 24V coil.
 

tomizett

Active Member
Mosfets have a pulsed forward current rating that is typically 4x the continuous
Just don't forget there are pulses and there are pulses.
A FET might typically have an SOA specified for a longest pulse of 10ms, where as I'd imagine that the startup surge of a pump (the time taken for the rotor to actually get spinning) could well be hundreds of ms - to the FET that might as well be DC.

I'm not contradicting Max, just making a cautionary note.
 
The word of automotive mechanical relays might be worth looking into as well, especially if you can find components specifically intended for lorries/trucks with 24V systems. Things like heater plugs and radiator fan easily draw this much current.

Of course, you may find yourself then needing a 5V coil relay to drive a main relay having a 24V coil.
I'm finding many 12VDC automotive relays with high current specs. Unfortunate they all seem to require a pig tail socket or a custom socket (not available), likely meant for installation in a fuse box. I'll keep looking. Though a search on amazon turned up some (questionable) SSRs that would do the job, and some less questionable options on eBay. It also turns out the relay I'm currently using is rated to handle the current load. I'm concerned about longevity and reliability switching (arching) such high currents, hence why I'm looking the direction of FETs and SSRs.
 

MaxHeadRoom78

Well-Known Member
. It also turns out the relay I'm currently using is rated to handle the current load. I'm concerned about longevity and reliability switching (arching) such high currents, .
This is why they make specialty ones such as the PRD version previously mentioned, fitted with arc blow out, using a magnet adjacent to the contacts.
Max.
 

AnalogKid

Well-Known Member
Most Helpful Member
The Bosch automotive relay, copied by the Tyco / P&B T90 series, is built for inductive DC loads. There are versions for control panel mounting - molded-in mounting ears and all 1/4" faston terminals. Omron also makes industrial control relays/contactors.

Or, check with your local HVAC shop/distributor. I just replaced the contactor in my AC compressor. 24 Vac coil, 50 A contacts.

If no one has mentioned it yet, be sure to put a suppression diode across the contacts. Something in the 10A series is cheap and beefy.

ak
 

crutschow

Well-Known Member
Most Helpful Member
If you don't need ground isolation between the control circuit and the motor, then you can just use a large MOSFET.
You can drive a "logic-level" type MOSFET directly with the micro 5V output.

Just make sure you have a power diode from the MOSFET drain to the +24V supply to absorb the inductive motor transient when the motor is turned off.
You can also put the diode directly across the motor but putting it at the MOSFET drain also absorbs any spikes from wire inductance.
Connect the diode anode directly to the MOSFET drain and its cathode to the +24Vdc.
Connect a 100uF capacitor directly from the diode cathode to the MOSFET source.
 

crutschow

Well-Known Member
Most Helpful Member
Although probably a good idea, do you need the kickback diode and snubber capacitor is using a SSR?
You'd have to look at the specs for the SSR to see if it has a snubber circuit built in.
 
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