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Thermostatic electric fan switch


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Recently went to start up BUO (TR6) after 3 months in storage and found the battery completely flat. Not just so low it wouldn't turn the engine, but so flat it wouldn't even illuminate the ignition light.

 

I've never had a battery this flat after this sort of period, especially as its a new 90 amp Bosh that was charged before layup.

 

I was thinking of what might have caused the discharge and was wondering if its the way I have cooling fan wired. I have a permanent live feed going to a relay that earths via a thermostatic switch in the radiator. In use, rad gets hot switch closes, earths relay, relay operatives turns on fan.

 

Now with he old fan which was a Kenlow with the sensor bulb in the top hose you did get a definite 'click' when the thermostat closed, with the new thermostat switch its doesn't appear to close in such an audibley positive way, and I was wondering if anybody knows if this type of thermostatic switch is actually fully open circuit when cold or if they simply provide an extremely high resistance when cold, if its the latter, then the way I have wired it still provides a high resistance path to earth and hence my totally discharged battery

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It would take a drain of around 40mA (or more) to do that in three months Graham, which is a resistance of 300 Ohms or less, which sounds unlikely. You could try to measure the drain if you have a suitable meter? I assume from your question that you are sure it wasn't something else like a radio or alarm system.

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It would take a drain of around 40mA (or more) to do that in three months Graham, which is a resistance of 300 Ohms or less, which sounds unlikely. You could try to measure the drain if you have a suitable meter? I assume from your question that you are sure it wasn't something else like a radio or alarm system.

Rob yes was wondering what else it could be, no radio or alarm fitted ...yet and things like lights ETC all turned off obviously, I've pretty much got, UOV the 3 sorted now so will put him into the storage unit and get back to work on BUO and try and track down where the volts are escaping

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You need to fit a battery isolator - then no milliamps can escape when you are not looking!

Also, an isolator is a safety factor - I use mine every time I park the TR.

Ian Cornish

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Ian,

 

Totally agree that a battery isolator is a good idea, and I am in the process of sorting one out for my car at the moment.

Do you have your switch so you can operate it from the cockpit?

(It’s not really practical to lift the bonnet each time you park.)

 

I was going to do it using an insulated pass through bolt (for the battery earth) that extends the earth cable to inside the car, through the bulkhead, and attach the switch to that. (I’ve done it on other cars and a bit of a faf, but it works.)

 

Do you have a better way?

 

 

Charlie

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Is your thermostat electronic? If so and as you’ve wired it to be active after engine switch off, as I have on Eric, then that would account for a small current drain.

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Is the Boot light turning off when the boot is closed. Put a camera set on video in the boot to see if the light goes out. As already stated anything electronic connected to the battery will drain it over time. The clock in my TR7 after three months has run the battery down. Its a around 30 mA. Modern TR!. I use a battery isolator.

 

Faulty components can drain the battery by developing a resistance to ground. These would be non ignition switched components, though it could also be the ignition switch.

 

You can test for current drain by placing a multi-meter in one of the main battery leads. i.e Remove one of the battery leads and place the multi-meter between this lead and battery. When carrying out this test ensure everything is turned off.

Before you connect the meter ensure it is in the highest current range. Once connected then work down to the lower current ranges to obtain a reading. If you do have a problem then disconnect each electrical component in turn until the drain stops. Then investigate that component. Be careful not to short any leads to ground as it will damage the multi-meter.

 

Dave

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Ian,

 

Totally agree that a battery isolator is a good idea, and I am in the process of sorting one out for my car at the moment.

Do you have your switch so you can operate it from the cockpit?

(Its not really practical to lift the bonnet each time you park.)

 

I was going to do it using an insulated pass through bolt (for the battery earth) that extends the earth cable to inside the car, through the bulkhead, and attach the switch to that. (Ive done it on other cars and a bit of a faf, but it works.)

 

Do you have a better way?

 

 

Charlie

One like this can be mounted under the hood with the key part through a hole to be actuated from inside the car.post-3379-0-05177600-1522857115_thumb.jpeg
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I have the battery isolator mounted on a bracket which is screwed to the bottom edge of the dashboard on the left side, so I just lean across to operate it. It does not have a removeable key, it's just a high-current rotary switch.

Ian Cornish

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Charlie said:

Quote: I was going to do it using an insulated pass through bolt (for the battery earth) that extends the earth cable to inside the car, through the bulkhead, and attach the switch to that. (Ive done it on other cars and a bit of a faf, but it works.). unqote.

 

Now that is a good idea!

I have installed a couple of main switches on the + side and was always concerned for shortcutting the potentially high current to earth.

Worst thing that can happen with a switch in the earth cable if you shortcut to earth is that the electrical system is activated.

are there any downsides to this great idea?

Regards,

Waldi

Edited by Waldi
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I failed to mention that my isolator is in the connection to earth (chassis/body), not on the positive side of the battery (I have an alternator, not a dynamo).

It's a slightly longer cable to reach as far as the bottom front of the dashboard.

I agree with Waldi that this is the safest method, although a rubber grommet in the bulkhead should ensure that the cable never has its insulation damaged.

I have been using this isolator since 1993 and, apart from one switch failing (easily replaced), with no problems.

Ian Cornish

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This thread has made me look through my box marked “Switches”, I thought I had an isolator switch somewhere.

 

I found this.

 

I now remember that I fitted it about ten years ago when I first started the rewiring part of my rebuild. Then for some reason I must have removed it. (Along with the rest of the loom, which I am now having to remake !)

 

This works for side screen cars. (Not sure about bulkhead arrangements for later cars.)

 

The upper (Brass) bus-bar is bolted directly to the sloping part of the bulkhead which has to be cleaned up to ensure good electrical contact.

 

The lower (Aluminium) bus-bar goes to the flat part of the bulkhead, with an insulated spacer between. An M8 bolt goes up through the lower bus bar, the insulating block, an oversized hole in the bulkhead, another insulating block, a brass “Eye” terminal and then the nut.

 

(I only used brass and aluminium because that was that I could find lying about.)

 

The earth lead from the battery is soldered to the terminal.(It’s actually the terminal that is already on the earth lead, and usually goes direct to the car body.)

 

What it means is that the knob for the switch is located just below the back of the glove box.

 

Amazing what you forget after ten years.

 

 

Charlie

post-14075-0-16950900-1523003095_thumb.jpg

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here you go.

Green things are headlamp relays, wiring to it comes through TR2 wiper rack hole.

battery master is to the right of them,

the spare accel cable is tucked behind pedal brackets

the footwell vent in the speaker hole on the right is ex TR7/8

 

Peter W

 

 

 

Edited by BlueTR3A-5EKT
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