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Old 02-27-2024, 11:25 AM   #1
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Please check my wiring

With switch open, path is from ECU to water pump with no path to 12V supply. When switch is closed, path is from power supply to pump with no path to ECU.


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Old 02-27-2024, 11:57 AM   #2
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What is this for? Is this engine/chassis wiring, or something inside for house wiring?
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Old 02-27-2024, 12:54 PM   #3
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Quote:
Originally Posted by Rucker View Post
What is this for? Is this engine/chassis wiring, or something inside for house wiring?
Why would it matter.

Sorry, those are screw heads in my drawing. Yes, red + black -.
Power to pumps comes from ECU when switch is open, from 12V supply when closed.

Pretend I actually know what I'm doing and the switch has a power source. I'm more interested in whether the paths are correct.
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Old 02-27-2024, 02:11 PM   #4
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Me thinks you can reduce this down to a DPDT relay instead of a 4 pole DT.

Pump pos/neg on the center poles, 9&10.
ECU, 5&6
12v supply, 1&2

I would also consider putting some blocking diodes on 5&6 in order to prevent a reverse current or noise/spikes from affecting the ECU.

In this manner, when you hit the toggle switch it will change contact positions and when you turn off toggle switch it goes back to the other position.

If you already have the 4 pole relay then just use half of it.

And not that it matters but sometimes it helps to understand what the project is when doing design work, but you explained it well enough for me.

ECU is controlling a water pump!

That is what your doing, isn't it ????

Something to consider is the current demand of the water pump. Can the ECU handle a high current output?

You might want to redesign this in a way that the small ECU current triggers a solid state, low current relay and use the outputs of that relay to push higher current.

By using this method you could eliminate the blocking diodes as the solid state relay would now isolate the ECU outputs from any potential back feeding.

I'm just cautious of putting to much of an electrical load on the ECU.

I am in no way saying your design is bad and I know you are just looking for a yes or no but identifying any potential harms to the ECU would be important enough for me, so I share this concern.

Just thinking ahead here...
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Old 02-27-2024, 03:32 PM   #5
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Why would it matter.

Sorry, those are screw heads in my drawing. Yes, red + black -.
Power to pumps comes from ECU when switch is open, from 12V supply when closed.

Pretend I actually know what I'm doing and the switch has a power source. I'm more interested in whether the paths are correct.
So to answer your question, yes the paths should work....but???

How much current flow on the water pump?

Today and then, tomorrow, especially when the motor wears down and pulls even more current ?
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Old 02-27-2024, 04:44 PM   #6
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This is the ECU that runs my heating boiler. Water pump is part of it and ECU supplies power to the pump in the original factory design. I need a way, when the boiler isn't running, to make the pump run.
I don't think it can be done with a DPDT. When the ECU is running the pump it is just a switch. When the ECU is off and the switch is on the other two contacts supply power to the pump. This way there is no possibility of getting power to the ECU that it may not like. I originally did it that way but wasn't happy with it, it worked that way for 5 years.

I was just asking about my paths. This is more what it actually looks like. Not sure how to draw the part one side is just a switch in a wire and the other side is suppling power.

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I do appreciate the feedback though.
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Old 02-27-2024, 05:15 PM   #7
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Electronics is my thing, started back in 1982...back in the fun days of repairing stuff!

How I miss Radio Shack parts!

Your paths will work just fine.

At first I thought you were going to tap power off the bus main ECU so that is why I had concerns about back feeding and current draw. I see now that is not the case. You ECU is actually the heater controller/brains ?? Which tells me that it will/can handle the pump motor current.

Drawing a straight line from top to bottom, dividing the 4 relay contacts to "left" and "Right"....

ECU powered -(left side) power goes in thru pins 9 & 10 and out thru pins 1 & 2 which then powers on the pump motor, (right side) 12 volts available to pins 11 & 12 but the circuit is open and cannot power the pump. wires to pump are at pins 7 & 8.

So the heater ECU turns off and now you have to manually turn on the pump using a toggle switch.

Toggle switch on/ECU off (right side) - turning ON the toggle switch energizes relay and wiper arms move to the other position bringing power to pins 7 & 8 which are jumper'd to right side pins 1 & 2.

So far so good this will work.

It can be done with a DPDT relay, you just got to wire the pump motor to the center poles and not the throws. this will eliminate the "jumper'd" wires mentioned above.

Also, if it is at all helpful to you, this can be wired to be switched automatically, so that when the ECU turns off, the relay toggles and automatically applies power to the pump. And for times when the pump is not needed at all (extended parking) a simple toggle on the 12v line to stop it from entering the relay contact.

Mind if I ask why this circuit is required for your application?

Would an automatic switching be helpful/upgrade ?

For an automatic circuit, you could also use a time delay relay so that it will switch on automatically and stay on until it times out and yes a toggle switch can still be used for full manual on-off control.
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Old 02-27-2024, 06:28 PM   #8
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Ah, misread your DPDT. I was thinking DPST. I'm gettin' old. Started chasing automotive sparks about 1965. I guess I was trying to make it hard. I'll draw up something.

Quote:
Mind if I ask why this circuit is required for your application?

Would an automatic switching be helpful/upgrade ?
This is my heat boiler. The pump is in a loop that the individual loop for each room draw from. Boiler is used for heat when stationary. When the engine is running I draw heat through an exchanger from the cooling system. I need to have the pump running to circulate water in the boiler loop (also for bleeding but, I've only had to ever do that once).
Actually automatic switching, with a way to turn it off, would be a plus, there have been a few times I've forgotten to turn the pump off and tried to start the boiler, it doesn't like that.
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Old 02-27-2024, 06:58 PM   #9
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This makes more sense. I haven't checked to see if ECU is switching power or ground. Are you thinking to use that as signal to make the switching automatic?

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Old 02-27-2024, 07:09 PM   #10
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Quote:
Originally Posted by somewhereinusa View Post
Why would it matter.

Sorry, those are screw heads in my drawing. Yes, red + black -.
Power to pumps comes from ECU when switch is open, from 12V supply when closed.

Pretend I actually know what I'm doing and the switch has a power source. I'm more interested in whether the paths are correct.
EWO seems to understand what the heck this is for.

Your heading 'please check my wiring' gives no indication of what you were looking for-and the fact that you're wired to an ECU made me think this was an automotive circuit, which you confirm in a subsequent post.

So it would have been helpful to say 'I'm trying to power my pump from two power sources', or such.

And again, if I understand what you are trying to do, EWO suggests a relay, which would be the easiest way to ensure only a single source of power at a time.

Is that the point?
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Old 02-27-2024, 08:27 PM   #11
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This makes more sense. I haven't checked to see if ECU is switching power or ground. Are you thinking to use that as signal to make the switching automatic?

Much better image!

I am gonna make some assumptions here, correct me if I'm wrong.

ECU output to power pump is 12vdc
ECU is chassis/battery grounded
ECU turned on by 12v - switch or thernostat ???


If the above is true then how would I wire it for automatic turn on ?

Connect pump to relay poles, not throws
Wire ECU outputs to the Normally open contacts of the relay
Splice/branch off from the ECU out 12v to the relay positive

On the normally closed contacts of the relay, this is where your external 12v gets wired, with a Toggle switch that lights up when powered.


Theory of operation:

ECU activates and sends 12v to relay contacts, which are normally open and also sends a 12v control signal to the relay which then closes the open contacts and the pump runs.

The second set of contacts on the relay, the Normally closed contacts, are now open and the external 12v is just sitting there waiting for the ECU to turn off and once it does turn off it then kills the 12v control signal to the relay which then resets the contact positions and now the ECU voltage at the relay is open and the external 12v contacts are now closed and is sending power to the pump.

The "lighted" toggle switch is si that you can see from a distance that it is turned on and also turn off the pump when you don't need it on.

If you want to get fancy, you could put an adjustable timer on the 12v supply line. They come in many different "time" packages, from seconds to minutes.
So that way you know that it would completely turn off when you fall asleep!

I hope that made sense... automatic operation!

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Old 02-27-2024, 10:04 PM   #12
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I'm going to table this for awhile I had to send the unit out for repair and can't do any testing until I get it back.

Thanks for the help.
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Old 02-28-2024, 09:47 AM   #13
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I'm going to table this for awhile I had to send the unit out for repair and can't do any testing until I get it back.

Thanks for the help.
No worries, glad I could help out !

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Old 02-28-2024, 06:18 PM   #14
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EWO seems to understand what the heck this is for.

Your heading 'please check my wiring' gives no indication of what you were looking for-and the fact that you're wired to an ECU made me think this was an automotive circuit, which you confirm in a subsequent post.

So it would have been helpful to say 'I'm trying to power my pump from two power sources', or such.

And again, if I understand what you are trying to do, EWO suggests a relay, which would be the easiest way to ensure only a single source of power at a time.

Is that the point?
My original drawing and question was about a relay, it is labeled 4PDT Relay. I was simply asking about the electrical paths. It doesn't matter if it is for automotive, it is in something automotive (bus) other than power and ground has nothing to do with the vehicle. Other things have ECU's (Electrical Control Unit)

EWO was kind enough to offer some suggestions and alternatives. I have taken some of his suggestions and made a new drawing of this simplified section of a much larger drawing as well as adding it to the larger much more complicated drawing.

I learned to read wiring diagrams and wiring schematics, they are different, over 50 years ago in the Navy. While things have changed A LOT basic electricity has not. I was simply asking if my paths were correct.
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Old 02-29-2024, 11:43 AM   #15
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Quote:
Originally Posted by somewhereinusa View Post
My original drawing and question was about a relay, it is labeled 4PDT Relay. I was simply asking about the electrical paths. It doesn't matter if it is for automotive, it is in something automotive (bus) other than power and ground has nothing to do with the vehicle. Other things have ECU's (Electrical Control Unit)

EWO was kind enough to offer some suggestions and alternatives. I have taken some of his suggestions and made a new drawing of this simplified section of a much larger drawing as well as adding it to the larger much more complicated drawing.

I learned to read wiring diagrams and wiring schematics, they are different, over 50 years ago in the Navy. While things have changed A LOT basic electricity has not. I was simply asking if my paths were correct.
Thanks for the clarification. Most people don't have 50 years experience, more like zero, so please forgive my second guessing. We've seen plenty of similar posts with a seemingly simple question on electrical, when in reality they are trying to drive a instapot off a cigarette lighter.

Glad Ewo was there for you.
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Old 02-29-2024, 12:10 PM   #16
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i went a mechanical route.. I found that both MP and davie's craig pumps as well as the chinesium once sourced by the diesel heater companies have pretty much 100% passthrough with little to no loss in flow.. I added a pump just past my diesel heater that I can turn on with a switch on the dash... if i run it with the diesel heater on it actually increases flow through the diesel heater.. with it off it doesnt seem to block any from when i didnt have it.. so when im running engine heat the second pump runs and I leave the diesel heater pump controlled just by its ECU...
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Old 02-29-2024, 02:28 PM   #17
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I thought about doing that, I have the pump and all of the wiring is basically there.
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