Wiper motor running hot.

[Tony]

Having thinking i had solved my wiper motor problems i now have the situation that it gets very hot when i turn on the ignition without the wipes turned on.The wipers do run at fast and slow speed but again it heats up and gets very hot.
I have heard that there is a supply coming from the park switch. Where is the park switch located so i can check this out.

Any thoughts would be appreciated. I would happily get the motor refurbed by Steve Hunt but want to check the problem is not elsewhere before blowing £200
Tony

[mach2andy]

Hi Tony
You don't say what series of car you have? Irrespective of the series of car, the problem is likely to be the motor windings. The insulation of the windings breaks down with age, leading to lower resistance and hence higher current flow. The higher current flow is what is most likely causing your motor to overheat. From memory, the overheating motor in my S2 car was drawing about 7 amps, and once rewound it was drawing about 2 amps.
If you can get your motor out and dismantled, you can send the armature [pictured] off to be rewound. Mine cost about £80 to be rewound. If your car is a series 2 car, the park switch is very simple to replace. It's the same switch that's fitted to a Mini, and I'm sure many other makes.

[Heuer]

The park switch is on the rack and can be accessed via the centre instrument console. There is no supply other than is simply provides an earth when activated.

Your wiring is wrong somewhere as there should be no current flowing unless the wiper switch is on or the park switch is active. In either case the motor would run. As yours is not running current is flowing, probably through the coil windings but not through the armature (or vice versa). I need to check on the wiring diagram to see if I can figure out where the problem is.

[Tony]

Hi Andy, my car is a series 1, positive earth. I have the motor off and have dismantled it looking for a problem.

David . I will check the supply to the parking switch when i manage to find it. I presume the black eArth wire coming from the wiper motor body goes to the park switch.??

Tony

[Heuer]

No the black earth goes to body earth. The park switch is a red wire IIRC and is temporarily earthed by the switch to provide power to park.

[abowie]

I'm suspicious that you have a short somewhere in the motor, possibly the armature, as suggested above.

[MarekH]

You most certainly have a short circuit, or something acting that way, so this needs to be sorted out.

The s1 wiper motor circuit has 12v power applied all of the time and the the wipers only run when the switch completes the circuit, either at the dash switch or at the parking switch in the middle of the scuttle.

The fact that it is running hot indicates that is where (or close to where) it is shorting to ground.

The amount of current drawn is inversely proportional to the resistance, so a component with a high resistance draws little current, whilst a low resistance component draws a high current. Usually, things don't get hot because useful work is done, but in this case, the low resistance between 12v and earth is not by design.



With the battery disconnected (remember it is all "live"), also disconnect the five pin plug under the wiper and check the resistances between the wires going into the wiper motor itself. If those are below the indicated values (e.g. 2ohms instead of 9ohms), then that is where your problem lies. Note that the diagram tells you that the resitances between any of the wires and earth are all infinitely high - i.e. they should draw no current if part of a circuit to earth on their own.

Being positive earth or negative earth is of no consequence here - electrical items work by either making a circuit (or not) between both battery terminals.

kind regards
Marek

[Heuer]

Marek

Tony measured the resistances whilst fault finding. See this post: http://forum.etypeuk.com/viewtopic.php?p=135966#p135966

"4. With the motor disconnected I get the following results

Yellow and brown wires = 10.8 ohms
Brown and white wires = 8.9 ohms"

This is probably a better diagram of the wiper motor circuit:

[Tony]

I have checked all the wires, colours and connections etc and they are connected as per the wiring diagrams. I was wondering if the circuit could be being made by the parking switch if is out of line or the red wire is running to earth causing a supply to the motor when the wiper are off. My next job is to check the parking switch. I did do a check on the ohms earlier on as suggested by David and seemed to get good results. I will check again to make sure.

Thanks again for everyones advice. I will crack this somehow.

[MarekH]

David,
That's only two of the checks for resistance listed on the diagram I referred to. Crucially missing are all of the single wires (on their own) to earth checks. (That's why I included that diagram, not the prettier one you posted - it is telling you that all of the wires have an infinite resistance to earth when measured separately.) The fact that the wipers work means that all of the "regular items" work and will probably measure within the expected spec, but something is getting hot and that means that something is also connecting to earth and drawing current, perhaps intermittently.

Tony,
Your wiper motor is always live and always has 12v on all the wires when not running. If any of the wires can find a path to earth, to complete the circuit, then the current that flows will either do useful work or heat something up. ("Always" means anytime the key is in the "run" position.) The wipers work because the switch (either at the dash and/or at the parking switch) completes the circuit to earth. Your job is to work out what else can complete a circuit to earth, i.e. provide a low resistance reading path to earth from any of the wires running into the motor. You must disconnect the battery to do that.

kind regards
Marek

[Tony]

I think i may have cracked it. I checked the park switch and it was running to earth as the wipers were not going back far enough to unearth the limit switch. This would also account for the motor running hot with the wiper switch off. It would also mean that this was on when the wipers were on . With the park switch on trying to send the motor clockwise and at the same time with the wipes being on trying to send the wiper motor anti clockwise at the same time. Does this make sense or am i barking up the wrong tree

I double checked the ohms and getting good readings.


Tony

[MarekH]

I'm not sure I understand that. The field winding and armature both have 12v and paths to earth so long as the park switch remains earthing (i.e. not going far enough). That means the wipers must keep running.

The difference between the slow running position and the stop position is that is that the switch on the dash has to connect 3 to 5 instead of 3 and 6 to 2 to force the parking switch into operation as the sole earthing source.

This means that if 3 cannot connect to 5 on the dash properly when you go to "off", the 1.5ohm armature remains connected to earth but the field winding cannot find a path to earth. The wipers will stop because only one of field and armature circuits is a complete circuit but the armature continues to consume 12/1.5 = 6 amps and heats up accordingly.

I'd check your dash switch is going to be reliable, in particular the 3 to 5 connection when it is set to the "off" position. Failure to do that means your armature will eventually burn out. This is what the thermal switch is there for.

Note that this explanation shows you how to generate a low resistance path to earth when the wipers are set to off, which is what you were asked to check. That's where your heat came from. So far, you've basically got lucky by turning the switch on and off so 3 to 5 connects for now, but I'm not convinced by the logic of your "fix".

Dismantle and clean the dash switch.

kind regards
Marek

EDIT:- for "3 to 5" read "3 to 5 OR 4 to 6" - if either one of those doesn't connect properly, the field circuit is broken in the "off" position and the wipers will thus stop but keep the armature connected via a malfunctioning park switch. Put simply, the park switch is only half of the problem.

[Tony]

Hi Marek,

I will check the dash switch and give it a clean. I will try and follow your logic on the single wire test. I am going through a long learning curve and I am finding it difficult to read the diagrams. While they show all the connection they do not show the which wires are connecting in the various switching position. for example

when ignition is turned to on.

1. The dash switch is off what wire are connected or disconnected.
2. The dash switch is on the slow position what wire are being connected or disconnected.
3. The switch is in the fast position what wire are being connected or disconnected.

Your explanation seems to show this but I just need to interpret it.

Regards

Tony.

[MarekH]

There is a very helpful pdf article written by the late Dick Vandermeyden which explains the wiper switch connections and how the wipers park. If you can find that then all should be clear. See https://newhillgarage.files.wordpress.c ... ticles.pdf This shows the switch positions, explains how it all works and the consequences of it not working.


Electricity does useful "work" when it makes a circuit and you can trace an uninterrupted path from the positive terminal of the battery to the negative terminal of the battery through the component where work is done.

When you can't complete a circuit, the electrical components are simply tied to whatever side of the battery they are still connected to, so in this case, because the switch is between the earth battery terminal and the wiper motor, the whole wiper motor simply sits at 12v, even when it is off, so long as the key is turned in the ignition.

Essentially, the wipers run when the field winding and armature winding are both circuits that are connected to 12v at one end and 0v at the other end (it has to make a circuit from one terminal of the battery to the other terminal). Any time that isn't true (i.e. if neither of them, or only one of them can complete a circuit), then they don't run.

The fault you have described was either an individual wire somehow completing a circuit OR a fault whereby both the parking switch and the dash switch contrived to let a low resistance item to stay connected. I describe it that way because you said it got hot.

If you unplug the 5way connector under the wiper motor, then you can determine whether the switch switches correctly at one end and whether the wiper motor resistances to earth are what the diagram says they ought to be at the other.

What needs to be worked out is how, with the switch settings you had, it was possible to either only have one of those circuits connected and still leave a low resistance path to earth OR have both of those circuits disconnected and have a low resistance path to earth, given that we know the wiper motor itself always remains connected to 12v at one end when the key is in the ignition.

kind regards
Marek

[Tony]

Thanks Marek. Extremely useful and the attachment by Dick Vandermeyden is very clear. If i manger open up the switch successfully i will photograph for future reference.

I would keep your head down for a bit as springs and metal ball fly all over the place when i open the switch.

Tony