Repairing 24V brushless heating pump?

[Timleech]

A customer has a failed 24V heating circ pump. It's based on a standard domestic ('Grundfos type') central heating pump. The mains motor has been changed for a (presumably) brushless DC motor

He's enquired about getting it repaired, and has had answers varying between 'No' and 'We can sell you a new pump for £500'.

 

The spindle turns freely with the power off, putting on the power holds it in one position.

 

Here are some pics of the electronics, looks pretty basic. To my untutored (read 'behind the times'!) eye appears to be four small power transistors, six smaller transistors(?) and a few standard resistors & capacitors. There are three sets of leads going from control board and disappearing into the motor case apart from the red & black pair (power in). Five leads which look to be the main motor leads. Six smaller leads which I'm guessing must come from a tacho/encoder. Three small leads, maybe speed control pot.

 

Pics of the innards:-

 

 

 

 

I'm looking for suggestions as to what checks I could make to track down faulty components, also is there a more or less 'standard' circuit for this sort of controller? If the motor windings are OK I reckon it should be within my capabilities to repair the circuit board as it's all discrete components. Nothing is obviously cooked, there's a little bit of corrosion on the PCB tracks.

I have decent multimeters and even an old oscilloscope hanging on the wall, not been used for a while but probably still works.

Alternatively, a pointer to someone who could repair for sensible money would be useful.

 

Thanks for any help

Tim

[Gibbo]

Two ways to tackle that:-

 

1. Painstakingly draw out the schematic, from that work out how it functions, then trace through the signals until you find one that isn't what it should be. Work out why not.

 

2. As there appears to not be much in it, test each component one by one. The components look like bog standard stuff so testing with a meter will be easy.

 

My favourite would be 2.

 

There are three basic ways that type of motor is driven.

 

A The controller just pulses the windings in the right order and hopes that the motor locks on. It does, but sometimes start up is a big ropey.

B The controller knows when to pulse the coils because it knows where the rotor is because it has hall effect sensors in it that tell it where it is.

C The controller knows when to pulse the coils because it monitors the changing emf from the coils as the rotor spins.

 

I would hazard a guess that one is as per B. If only because it's the simplest to design.

 

Gibbo

Edited August 22, 2009 by Gibbo

[Timleech]

Two ways to tackle that:-

 

<snip>

 

I would hazard a guess that one is as per B. If only because it's the simplest to design.

 

Gibbo

 

Thanks for that.

I've just found the pump on the web:-

 

http://www.digitelpumps.com/Pump-english.php

 

I've emailed them in case they have a recommended repairer in the UK.

 

Tim

[Semitrad]

I suppose that if you have a reference book of semiconductor types and know what readings to expect when you test with your multimeter it's possible to test the active components - as long as you desolder at least two of the three legs from circuit. If you don't have this knowledge then blanket replacement might be the way to go, still cheaper than £500 but very time consuming, see thread on repairing inverters.

[pirate paul]

A customer has a failed 24V heating circ pump. It's based on a standard domestic ('Grundfos type') central heating pump. The mains motor has been changed for a (presumably) brushless DC motor

He's enquired about getting it repaired, and has had answers varying between 'No' and 'We can sell you a new pump for £500'.

 

The spindle turns freely with the power off, putting on the power holds it in one position.

 

Here are some pics of the electronics, looks pretty basic. To my untutored (read 'behind the times'!) eye appears to be four small power transistors, six smaller transistors(?) and a few standard resistors & capacitors. There are three sets of leads going from control board and disappearing into the motor case apart from the red & black pair (power in). Five leads which look to be the main motor leads. Six smaller leads which I'm guessing must come from a tacho/encoder. Three small leads, maybe speed control pot.

 

Pics of the innards:-

 

 

 

 

I'm looking for suggestions as to what checks I could make to track down faulty components, also is there a more or less 'standard' circuit for this sort of controller? If the motor windings are OK I reckon it should be within my capabilities to repair the circuit board as it's all discrete components. Nothing is obviously cooked, there's a little bit of corrosion on the PCB tracks.

I have decent multimeters and even an old oscilloscope hanging on the wall, not been used for a while but probably still works.

Alternatively, a pointer to someone who could repair for sensible money would be useful.

 

Thanks to these I do not have central heating. I am gona have to pass on this one, I would be interested to know how you get on though....

Any chance of loads more pics and detailed description for the hard of thinking.... I can see the transistors etc what all those wires are for ????????????????

Try BAEC British amateur electronics club.

Keep going on this thread, I am reading it.

This is the reason why

[pirate paul]

This is the reason why

That did not come out right.

That is the reason I do not have central heating, keep us updated interesting stuff, diagrams descriptions more pics please....

I have not got the foggiest what is wrong with it, just interested in how it works.

[RLWP]

B The controller knows when to pulse the coils because it knows where the rotor is because it has hall effect sensors in it that tell it where it is.

 

I would hazard a guess that one is as per B. If only because it's the simplest to design.

 

Gibbo

 

If it is B, does that mean that there is an additional magnetic thingy fitted to the rotor for the hall-effect sensor to sense. If so, has it fell off?

 

Richard

[Timleech]

If it is B, does that mean that there is an additional magnetic thingy fitted to the rotor for the hall-effect sensor to sense. If so, has it fell off?

 

Richard

 

I'm beginning to suspect a problem with the Hall sensor or whatever else has been used.

 

Here's my attempt at one half of the circuit, it's really two identical circuits though they're probably linked in some way to keep each other in sync:-

 

EDIT to add that the one obvious link between the two parts is that the rail in the centre of my sketch, fed with a diode from B+, is common between the two parts.

 

 

Notes:- I've shown some items as capacitors, where they may be something else.

They're the orange components with a black ring in the next pic.

 

I'm very rusty at this sort of thing so probably haven't followed conventions (don't laugh too much!).

 

the 'two white' at the top of the sketch should read 'two black'

 

M1, M2 are two of the four motor phase windings

 

 

Tim

Edited August 23, 2009 by Timleech

[MoominPapa]

I'm beginning to suspect a problem with the Hall sensor or whatever else has been used.

 

Here's my attempt at one half of the circuit, it's really two identical circuits though they're probably linked in some way to keep each other in sync:-

 

EDIT to add that the one obvious link between the two parts is that the rail in the centre of my sketch, fed with a diode from B+, is common between the two parts.

 

 

Notes:- I've shown some items as capacitors, where they may be something else.

They're the orange components with a black ring in the next pic.

They look more like diodes to me, probably different value zener-diodes. They maybe bias the hall-sensor circuit such that the power transistors turn on earlier or later in the cycle. The leftmost and righmost pairs of transistors are darlington pairs to switch the motor phases, and the middle transistor inverts the signal so that one phase is off when the other is on, I think.

 

But I'm rusty too.

 

 

MP.

[Timleech]

They look more like diodes to me, probably different value zener-diodes. They maybe bias the hall-sensor circuit such that the power transistors turn on earlier or later in the cycle. The leftmost and righmost pairs of transistors are darlington pairs to switch the motor phases, and the middle transistor inverts the signal so that one phase is off when the other is on, I think.

 

But I'm rusty too.

 

 

MP.

 

Here's a revised version, they're shown as plain diodes that would make no sense, whereas Zeners probably would.

 

 

Tim

[smileypete]

Hi,

 

I'd try swapping the connections to the motor windings and position sensors, then see if the rotor locks in the same place.

 

That should narrow it down to the controller or motor itself.

 

cheers,

Pete.

[Yoda]

It's yer lack of thermionics!

[pirate paul]

They look more like diodes to me, probably different value zener-diodes. They maybe bias the hall-sensor circuit such that the power transistors turn on earlier or later in the cycle. The leftmost and righmost pairs of transistors are darlington pairs to switch the motor phases, and the middle transistor inverts the signal so that one phase is off when the other is on, I think.

 

But I'm rusty too.

 

 

MP.

I was going to say they look like diodes( I wasnt gona say zener mind you) you learn something every day...Still reading this keep up the good work...what about a diagram for the other half please...........

[paulcatchpole]

I would hazard a guess that one is as per B. If only because it's the simplest to design.

Gibbo

 

So Mr G, are these conventional AC central heating pumps with a DC drive circuit, or is the motor swapped?

 

PC

[Timleech]

I was going to say they look like diodes( I wasnt gona say zener mind you) you learn something every day...Still reading this keep up the good work...what about a diagram for the other half please...........

 

The other half is basically the same, the two halves are linked via the 'speed' rail and the rail in the middle with all the diodes going to it, there's only the one speed switch & associated 'diodes'. There's a resistor missing from my sketch, links -ve and the speed rail.

Have to leave it now & get on with something else for a few days. I'm only 'playing' up to now out of curiosity, but the customer will get a bill if I succeed

The motor windings and case are special, the rotor might be standard from a mains pump, dunno.

 

Tim

[pirate paul]

The other half is basically the same, the two halves are linked via the 'speed' rail and the rail in the middle with all the diodes going to it, there's only the one speed switch & associated 'diodes'. There's a resistor missing from my sketch, links -ve and the speed rail.

Have to leave it now & get on with something else for a few days. I'm only 'playing' up to now out of curiosity, but the customer will get a bill if I succeed

The motor windings and case are special, the rotor might be standard from a mains pump, dunno.

 

Tim

Well I dunno myself but if you are too busy, or etc.....

I will give you a tenner for it as is.

 

I look forward to further lectures from your obviously well experienced self.

 

When is the popcorn lady coming round... its gettin a bit chilly here on the back row.

[Timleech]

Well I dunno myself but if you are too busy, or etc.....

I will give you a tenner for it as is.

 

I look forward to further lectures from your obviously well experienced self.

 

When is the popcorn lady coming round... its gettin a bit chilly here on the back row.

 

Sorry, not mine to sell....

Been away for a few days, including 6 hours static on the M5 on Friday , now have to earn some money but will get some more time on it before long.

 

Normal service will be resumed....., etc

 

Tim

[steelaway]

Hi

 

I think you are all barking up the wrong tree.

I have tried to repair CH pumps in the past and I have always failed.

The clearance between the rotor and the magnetic stator is only a couple of thou. When the rotor bearings (bronze bushes) have worn out the rotor tilts over and sticks to stator as soon as power is applied.

It is normal for this to happen after a few years of use and I have been able to replace the bearings.

IMO you need a new pump.

 

Alex

[Gibbo]

Send it to me. I'll fix it while I'm picking my nose.

 

Gibbo

[pirate paul]

Hi

 

I think you are all barking up the wrong tree.

I have tried to repair CH pumps in the past and I have always failed.

The clearance between the rotor and the magnetic stator is only a couple of thou. When the rotor bearings (bronze bushes) have worn out the rotor tilts over and sticks to stator as soon as power is applied.

It is normal for this to happen after a few years of use and I have been able to replace the bearings.

IMO you need a new pump.

 

Alex

 

Where can I get a 12 or 24v central heating pump?

[ThePiglet]

Where can I get a 12 or 24v central heating pump?

It's not the traditional household type pump, but Eber and Webasto suitable.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?Vie...em=400068176577

[Timleech]

Hi

 

I think you are all barking up the wrong tree.

I have tried to repair CH pumps in the past and I have always failed.

The clearance between the rotor and the magnetic stator is only a couple of thou. When the rotor bearings (bronze bushes) have worn out the rotor tilts over and sticks to stator as soon as power is applied.

It is normal for this to happen after a few years of use and I have been able to replace the bearings.

IMO you need a new pump.

 

Alex

 

Interesting & maybe useful observation, though you do seem to be contradicting yourself

(can't be fixed/can be fixed )

 

Tim

[pirate paul]

It's not the traditional household type pump, but Eber and Webasto suitable.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?Vie...em=400068176577

Nice one.

[pirate paul]

Send it to me. I'll fix it while I'm picking my nose.

 

Gibbo

How about fixin it holdin a camera, discribe each component, current through it, voltage across it, and how to (I am not sure of the words), make a signal go through it and trace that signal.

 

Less your chickin.