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Tach signal from an Electric Water Pump?

Greg72

Greg72

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OK here's my oddball question for the week:


Let's say you were interested in running an electric water pump on your motor, but were concerned about reliability for a street-driven vehicle.

It would be nice to know that the waterpump was spinning by having a "signal" wire....the way some fan motors do (positive, ground, and tach/signal wire)....that way, you could have it connected to one of those Autometer monster warning lights, and if the tach signal ever "went away" while driving, the warning light would instantly light up and let you know you are no longer circulating coolant!!!

It would sure be good "piece of mind"...and might make the decision to run an electric pump a little easier. Does anyone know of a company that makes an electric pump with this feature, or if there's a way to somehow monitor an inductive signal on the motor or power leads to effectively do the same thing????


Like I said....weird. Sometimes this is the stuff my brain wonders about. There is no logical reason why. /forums/images/graemlins/grin.gif
 
The best way would be to have a small magnet located on the spinning part of the motor and a pick-up sensor on the stationary part of the pump. I think you would have to custom build something like that. You could probably find a very simple schematic on the net somewhere.
My only question is: Doesn't the pump only come on when the temp. reaches a certain point, then it circulates the coolant and stops flowing?
 
Wouldn't your temp guage serve the purpose? If the water pump stops spinning the temp will rise indicating something is wrong. It's no different than if a mechanical water pump went bad or threw a belt.
 
Well the easiest way would be to build a simple current sensing circuit on the power supply to the pump. You can set a reference current level and if the current drops below this it can turn an led on or send some other a/d signal to something.

Basically you just put a sense resistor on the power supply running to a comparator such as a LM393. You will set up your sense resistor and bias voltage to what you want your current minimum to be and be done.

There are various other components readily availabe to build the same circuit as well.
 
I thought about that, but I have seen many broken fans/motors that are stuck in one position and don't rotate, yet they still draw current. /forums/images/graemlins/eek.gif
 
ok, i like asking questions, why does no one recommend an electic pump for street, only for drag?
 
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Wouldn't your temp guage serve the purpose? If the water pump stops spinning the temp will rise indicating something is wrong. It's no different than if a mechanical water pump went bad or threw a belt.

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I'm trying to avoid using a gauge (and the requirement that I notice it climbing at the precise moment when the failure occurs).... by then, the damage may already be done.

Kinda like asking me to watch for low oil pressure....if there is a way to DRAMATICALLY signal me that somethings wrong, I'd be a lot more relaxed when I drive, and not frantically watching every needle on the dash....


Anyway, that's the theory. /forums/images/graemlins/smile.gif
 
In that case I would raid a surplus motor store and buy a tach. Drill and tap the backside of the motor shaft and attache the tach and use it's pulse output. Rig up a small counter circuit and if the thing stops pulsing then turn a light on.

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I thought about that, but I have seen many broken fans/motors that are stuck in one position and don't rotate, yet they still draw current. /forums/images/graemlins/eek.gif

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ok, i like asking questions, why does no one recommend an electic pump for street, only for drag?

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No personal experience but from what I have read at www.chevytalk.com the electric pumps just don't give the cooling flow capacity necessary for street use. For short 1/4 mile runs they say they are fine, but not for extended use.
 
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I'm trying to avoid using a gauge (and the requirement that I notice it climbing at the precise moment when the failure occurs).... by then, the damage may already be done.

Kinda like asking me to watch for low oil pressure....if there is a way to DRAMATICALLY signal me that somethings wrong, I'd be a lot more relaxed when I drive, and not frantically watching every needle on the dash....


Anyway, that's the theory. /forums/images/graemlins/smile.gif





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You set up an adjustible temperature switch to energize a light on the dash when the engine temperature rises above normal. Not hot as in vehicles with idiot lights, but adjust it to a temperature just above the hot side of normal operating temperature. You could certainly respond to the problem then before any long term damage happened.
 
Thats way to easy for greg, he needs something fancy and complicated /forums/images/graemlins/rotfl.gif
 
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Thats way to easy for greg, he needs something fancy and complicated /forums/images/graemlins/rotfl.gif

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Somewhat true I suppose......

The problem with a tempurature-sensing light is that it is not a "conclusive" warning system. It MIGHT be indicating a waterpump failure, but then again it might just be telling me that I'm doing a tough climb on a hot day.
 
You could have a few different temp sensors that sense for different temps and as the temp gets higher, the yellow green light comes on, then the orange, then the red, etc.
 
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You could have a few different temp sensors that sense for different temps and as the temp gets higher, the yellow green light comes on, then the orange, then the red, etc.

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It's still basically the same problem......what does the temp tell me???? I still don't know for certain that there's been a pump failure, and that is my primary concern....

I don't know if the electric water pumps are reliable enough (despite what the manufacturer will tell you) for a street driven vehicle. Having a tach output, or motor sensing circuit of some kind would help to remove some of the uncertainty.

I actually think it would be cool to have a toggle switch on the dash so that the "real" tach could indicate either engine RPM or water pump RPM depending on the position of the switch..... but I'd still like the BIG RED LIGHT too.

/forums/images/graemlins/smile.gif
 
Tim,

How does a diesel tach work? I just realized "diesel" means no plugs.....so how does it get a timing signal?


/forums/images/graemlins/thinking.gif
 
You could get a temp light - I use the Autometer Oil Pressure light to tell me if I loose oilpressure for whatever reason.

You could buy the Temp Light and install whatever sending unit you have. But, I would never stray away from having a gauge. We all know how it feels to be stranded on the side of the road with those darned Idiot lights! You need to be able to monitor things a little closer than with lights - or, at least I do. /forums/images/graemlins/thumb.gif

http://store.summitracing.com/product.asp?d=10&s=209&p=149&searchtype=ecat
 
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Tim, How does a diesel tach work? I just realized "diesel" means no plugs.....so how does it get a timing signal?
/forums/images/graemlins/thinking.gif


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I've seen three different methods for triggering a tach on a diesel. First is simple, use an inductive pick-up pointed at the ring gear teeth. A circut in the tach is programed for the number of teeth and divides the time based reading by this number. Second method is also inductive. The fuel pulse going to any cylinder creates a small magnetic field. Put an inductive pick-up on any injector's supply tube and that will trigger the right tach circut. Third method is a bit more difficult, the alternator has an AC tap that the tach is connected to. By reading the frequnecy and factoring in the alt's drive ratio crank speed can be deduced.

For your original Q I'd pick a pump with a fixed (i.e. not a rubber) impeller and use an inductive pick-up to sense whether it's rotating or not by positioning the pick-up's core where each impeller lobe/vane will pass over it. A simple circut could analyze whether the pick-up were sending impulses and when not, turn on a light.
Another method would be to use a pressure sensor on the outlet of the pump. With a little dialing in you could tell if the impeller were spinning by the water discharge pressure or the lack thereof. Key to this plan would be a pressure sensor with a small hysteresis and very fine resolution.
 
just get a old motorcycle tach that are mechanical. don't know how you would hook it up the the cable is identicle to a speedo cable. you may not get it calibrated correctly but it would tell you if it was not spining.
 
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