Small dash gauge motor / possible rewinding

[sako243]

I know there's a few people into restoring classics etc., and there's a broad reach of knowledge on this forum.

Essentially I've been tasked with fixing a mates Ford 655D back hoe's fuel gauge. It's an odd moving coil setup and one of the windings is broken. I've got an X27-589 stepper motor (which is used in a lot of instrument clusters) working but it's too big or rather wrong shape. It's an old Jaeger fuel gauge that is no longer available and was only used for a very small run of machines by the looks of it.

There's not a lot of height to play with the grey board up the top is the decal plate. The M3 standoffs sink into clips on the carrier board so everything needs to stay above the threaded portion. A grand total of 16.2mm to play with.

Now the above has been designed and would work except...

The motor sticking out past the PCB means it doesn't slot into place. The pivot point has been kept the same to keep the geometry the same

So does anyone have any bright ideas? The mechanics of things means that the whole thing needs to fit under the decal plate (there is a bit of leeway but we're talking millimeters).

Currently winning is to come up with some tiny linkage to relocate the motor (that in itself is no mean feat because of causing clashes elsewhere).

 

[Kram]

Cut the casing to give motor the extra space needed and epxy it sealed afterwards. The casing looks thick enough to give the required clearance.

 

[sako243]

Illusion because of a flange around the top for it to sit in the dash if you're talking about the whole housing for the dash? Wall is only a couple of mm thick there.

 

[EBME2]

How original does it need to look or the owner want it to be? If they aren’t too bothered could you replace with an LCD display? Obviously if they want to preserve originality then a none starter.

 

[frank horton]

look at places like Egypt, Morroco.....even Greece, there a lot of old stuff still working....
I got a load of brand new obsolete engine parts from Cairo not that long ago...
it was easy with no probs via Ebay.....

 

[sako243]

Obviously if they want to preserve originality then a none starter.

This. Would have been trivial if he didn't want originality.

look at places like Egypt, Morroco.....even Greece, there a lot of old stuff still working....
I got a load of brand new obsolete engine parts from Cairo not that long ago...
it was easy with no probs via Ebay.....

I've had a brief look but he's done a lot more plus has useful contacts. The main issue is that this particular model the D was a sort of transition model that wasn't made for very long. Ford decided to make their own dash for it, older models are readily available and common with other stuff, later models they used digital dashes from New Holland's tractors so there's a very narrow window where this particular dash was used. According to Ben anyway and he's spent the best part of a year finding out.

I'll measure up the angles on the gauge and add them into the model to see if I can make it work with a slightly offset motor. Failing that I think the best approach to try next is some kind of mini linkage like a wiper arm to connect the needle to the motor spindle allowing me to offset it. Height is a real bugger on this one, well as is space to be honest.

The old setup was a kind of moving coil arrangement, there is the possibility of rewinding it but annoyingly the winding that is broken is the inner one which means unwinding what looks like thousands of turns of tiny enamelled wire from the other one first. I have tried to see if the broken bit is near the terminals but it doesn't appear to be.

 

[Martin-Sy]

Anything from the radio control model stuff suitable? There are some very small servos. Eg This
Dims 20x17x 8.6

 

[sako243]

Anything from the radio control model stuff suitable? There are some very small servos. Eg This
Dims 20x17x 8.6

I have had a bit of a hunt through those but they tend to be fairly deep and more powerful than needed which inherently means more circuitry required to drive it which makes things even tighter to fit.

The one you linked above I don't think would fit because again the spindle to wall distance for the gauge is about 3.5mm if I recall (would need to double check. It's close enough to see but I suspect the height may be an issue as it looks to be 20mm from bottom to the spindle and ideally I need that to sit inside 17.7mm. It might be doable with a tweak to the needle as thankfully that is mostly hidden at the pivot point.

 

[GRW]

Sorry if this is s dumb question from a non-electronics hack..... but could the gauge be made/adapted to operate off a variable resistor type float?

(I have a dial gauge for my campervan water tank - & that uses a 0-190 Ohm vertical float to a solid state but analogue needle-sweep gauge. I wondered if something similar might work )

 

[sako243]

but could the gauge be made/adapted to operate off a variable resistor type float?

It's the gauge that is broken and NLA, this is how it should work. The sender appears to be fine but one of the windings in the gauge is broken.

So I need to make the needle move according to the resistance from the sender.

 

[GRW]

It's the gauge that is broken and NLA, this is how it should work. The sender appears to be fine but one of the windings in the gauge is broken.
View attachment 530842
So I need to make the needle move according to the resistance from the sender.

"One of the windings"?
Is the winding in question a wire-wound resistor/potentiometer?
Could that part be replaced/substituted?
(I'm sure you've considered this already)

 

[sako243]

That's the back of the gauge. As I said it's a slightly odd moving coil setup with the two windings "opposing" each other and the sender forming a bias on one of the legs to pull the needle one way or t'other.

Annoyingly it looks like the "reddish" winding is the one that's gone so you'd have to rewind the gold one as well.

Could that part be replaced/substituted?
(I'm sure you've considered this already)

I mean it's just winding some wire but as you can see on the photo it's tiny enamelled wire and lots and lots of turns. I don't know enough (yet) about the characteristics as to whether the type of wire matters along with the number of turns to get the needle to move accurately.

 

[GRW]

View attachment 530844
That's the back of the gauge. As I said it's a slightly odd moving coil setup with the two windings "opposing" each other and the sender forming a bias on one of the legs to pull the needle one way or t'other.

Annoyingly it looks like the "reddish" winding is the one that's gone so you'd have to rewind the gold one as well.


I mean it's just winding some wire but as you can see on the photo it's tiny enamelled wire and lots and lots of turns. I don't know enough (yet) about the characteristics as to whether the type of wire matters along with the number of turns to get the needle to move accurately.

I'd guess the number of turns would be pretty important.
What an odd setup!

It's like you say - that there is an increasing & decreasing resistance in each coil - and its the differential value that determines needle position?

So what makes the gauge actually move/indicate? I can see the variable resistance float, & a constant DC voltage through those coils - so is the needle actually responding to a variable voltage value through the coils (like coil A volts less coil B volts determines needle position

 

[Seadog]

Annoyingly it looks like the "reddish" winding is the one that's gone so you'd have to rewind the gold one as well.

That was inevitable, of course. A perfect demonstration of Sod's Law

 

[Agroshield]

Can you offset the motor so it fits and then use a pair of equal gears between motor and indicator bar. The motor would need to turn in the opposite direction. As it may not be a full revolution, a pair of sector (part) gears could also help in the space.

How much of the motor casing in that area is necessary for its function? Maybe that could be shaved as well as the housing. Can the decal plate be moved upwards in its window?)

 

[sako243]

Can you offset the motor so it fits and then use a pair of equal gears between motor and indicator bar. The motor would need to turn in the opposite direction. As it may not be a full revolution, a pair of sector (part) gears could also help in the space.

That has been a consideration, it'd be tricky space wise to actually fit something in there, this is watch makers tereitory rather than Land Rover gears . I'm not ruling it out but if I can avoid it it would be nice.

How much of the motor casing in that area is necessary for its function? Maybe that could be shaved as well as the housing. Can the decal plate be moved upwards in its window?)

Unknown, they're cheap enough I could sacrifice one to find out.

Moving the decal plate upwards is not really possible. I mean it is a little bit but then I'd have to move the coolant gauge next to it up the same amount and possibly shave down the fascia panel.

 

[sako243]

So what makes the gauge actually move/indicate? I can see the variable resistance float, & a constant DC voltage through those coils - so is the needle actually responding to a variable voltage value through the coils (like coil A volts less coil B volts determines needle position

Yes I think so. Think back to school days with 9V batteries, screw drivers and wire to make electromagnets. More windings means a stronger electromagnet.

In this instance when the tank is empty and therefore low resistance on the sender the right hand coil is effectively shorted out down to ground so the right cool is inactive. When the tank is empty and the sender high resistance then both coils are active but the needle and biasing of the coils must be done in such a way that the needle points right. There's a little butterfly shape at the base of the needle which is clocked on way presumably for this exact reason.

In some respects it's quite neat because it automatically dampens the sender.

 

[GRW]

Given the Senders are the same variable resistance type.... then could you perhaps buy a cheapy (£20 ish) typical 45-55mm circular gauge off EBay.... rob the guts out of it & graft them in?

 

[Bullet2012]

I understand that visteon took over the instrument manufacturing from Ford, they used to have a factory in Brimsdown/Ponders End

 

[m_c]

Somebody who does guitar pickup winding, should be able to rewind a couple simple coils like that.

I do know one who might be interested. I can ask him if you want?