Is this even legal? :)

I'm almost finished with my retrofit but have hit a snag.

I have the DMM DMB4250-8B breakout board (https://www.dmm-tech.com/DMB4250-8B_main.html)

According to the manual it says D16 and D17 can switch on a relay up to 30vdc @ 50mA (page 12 https://www.dmm-tech.com/Files/DMB42...tVer010106.pdf)

I have 12vdc in the cabinet and don't really want to add another power supply due to space so I'm working with 12 volts as the coil voltage for a magnetic contactor. Problem is, I have been unable to find a magnetic contactor at 12 volts with a coil amperage so low. The smallest one I could find is here (https://www.automationdirect.com/adc...4aAoj4EALw_wcB) and after contacting WEG they say it's 1.7w which puts it at 141mA if my math if right.

Here's my wacky idea. Can I use a small automotive 12v relay, plenty available at 50mA or under, and use that relay to turn on the magnetic contactor? Basically, run 12 volts to both and have the auto relay hooked to the breakout board and the magnetic contactor connected to the relay. BB closes the circuit when prompted, and turns on the small relay which in turn turns on the large relay.

Dumb idea???

Not wacky or dumb. Have you looked for an SSR they will switch with low current too. Although I thought you would have had no trouble finding a relay or relay board to suit.

Sent from my SM-N970F using Tapatalk

Quote:

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Originally Posted by boydage

Not wacky or dumb. Have you looked for an SSR they will switch with low current too. Although I thought you would have had no trouble finding a relay or relay board to suit.

Sent from my SM-N970F using Tapatalk

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I was today years old when I learned about SSR's. Took about 5 minutes of looking and found this one here - https://www.automationdirect.com/adc...ssr610-dc-280a


From the tech specs it looks like it might only draw 16mA on the switch side. Well below the limit if I'm reading it right.

Attachment 475304

THANKS!!!

Hi,

SSR's are brilliant, I bought this a wee while ago:

https://nz.element14.com/durakool/sr...nel/dp/2918602

The DC current to turn on is less than 20mA, and any voltage from 4VDC to 32VDC....easy.

Craig

Quote:

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Originally Posted by ecdez

I was today years old when I learned about SSR's. Took about 5 minutes of looking and found this one here - https://www.automationdirect.com/adc...ssr610-dc-280a


From the tech specs it looks like it might only draw 16mA on the switch side. Well below the limit if I'm reading it right.

Attachment 475304

THANKS!!!

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You need a DC SSR not an AC, what you are looking at has in DC in but AC switching, you will need DC input and DC switching output for what you are wanting to do.

Hi,
so what are you trying to switch, AC or DC?.

Most contactors are for switching AC power in which case an SSR is the contactor, its just that it can be controlled with a sub 20mA low voltage signal.

Craig

I might be looking at the wrong one, not sure.

The voltage to turn the relay on will be 12 volt dc (max 50mA).

The load I'm trying to turn on is 120ac for a small coolant pump.

Am I looking at the wrong relay?

Hi,

Quote:

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The voltage to turn the relay on will be 12 volt dc (max 50mA).

The load I'm trying to turn on is 120ac for a small coolant pump.

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Then an SSR will be perfect, you don't need a contactor, the SSR does the job on its own. This is almost an identical purpose for which I bought
my SSR. I wanted to turn my coolant pump (240VAC) on and off, and my BoB signals 24V up to 50mA.

The SRR will work with any DC control voltage from 4VDC to 32VDC and under 20mA, so your 12V 50mA signal will be fine.
It can switch anywhere from 24VAC to 240VAC at up to 15A, so it will switch your coolant pump on and off no trouble.

So you don't need a contactor or a relay...just an SSR.

Craig

Quote:

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Originally Posted by ecdez

I might be looking at the wrong one, not sure.

The voltage to turn the relay on will be 12 volt dc (max 50mA).

The load I'm trying to turn on is 120ac for a small coolant pump.

Am I looking at the wrong relay?

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I thought you were switching a 12v Coil on a contactor, that's what your post read. if so then you need the SSR-DC Relay if you are switching direct to the pump then you would need an SSR-AC Relay

The Breakout Board side can be 3-32v DC you have 12v for that, so the contactor you are switching the coil you said was 12v

You can use the SSR and not have the contactor that then would be an Ac SSR to suit the coolant pump motor spec's.

Try this https://www.amazon.com/AEDIKO-Channe...s%2C135&sr=8-6

Quote:

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Originally Posted by joeavaerage

Hi,



Then an SSR will be perfect, you don't need a contactor, the SSR does the job on its own. This is almost an identical purpose for which I bought
my SSR. I wanted to turn my coolant pump (240VAC) on and off, and my BoB signals 24V up to 50mA.

The SRR will work with any DC control voltage from 4VDC to 32VDC and under 20mA, so your 12V 50mA signal will be fine.
It can switch anywhere from 24VAC to 240VAC at up to 15A, so it will switch your coolant pump on and off no trouble.

So you don't need a contactor or a relay...just an SSR.

Craig

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Joe has it right here.
However you must be careful about where you use a SSR. Many of them don't turn OFF completely. The cheap one's have a leakage current that will still provide a voltage at the output. This should not be a problem when running a motor for a pump, but in some situations it can cause a problem.

Hi,

Quote:

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However you must be careful about where you use a SSR. Many of them don't turn OFF completely.

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That is quite correct, the unit I linked to has a max leakage current of 7mA, so its not too bad.....but I'd never trust it to isolate the circuit if I were working on it....no way!

Craig

Quote:

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Originally Posted by maxspongebob

Joe has it right here.
However you must be careful about where you use a SSR. Many of them don't turn OFF completely. The cheap one's have a leakage current that will still provide a voltage at the output. This should not be a problem when running a motor for a pump, but in some situations it can cause a problem.

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This only happens if you buy the cheap Chinese SSR's, using quality brand name SSR's and this does not happen.

Quote:

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Originally Posted by ecdez

I might be looking at the wrong one, not sure.

The voltage to turn the relay on will be 12 volt dc (max 50mA).

The load I'm trying to turn on is 120ac for a small coolant pump.

Am I looking at the wrong relay?

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Whatever SSR you get, one feature it will need for switching a motor load is (Zero Crossing) look for this in the spec's, nobody has mentioned this in their posts.

You can also switch the SSR direct from the Breakout Boards 5v signal, don't need to add in the 12v