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Dart electrics

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silverdart
Posts: 285
Joined: Sat Feb 13, 2016 10:49 am
Location: West Midlands

Dart electrics

Post by silverdart »

Hi All, I was out driving recently and the electric cooling fan was operating. At one point I needed to re-start the engine at which point the starter motor turned the engine over at the usual speed but it would not start. I tried numerous times but no go.
After waiting a few minutes the fan had stopped and the engine started immediately.
Could it be that something in the electrical circuitry is not performing correctly or do I need to manually switch off the fan whilst I restart the engine.
All help appreciated.

Dave.

A.N.Other
Wide Man
Wide Man
Posts: 551
Joined: Tue Feb 16, 2016 12:45 pm
Location: Leeds

Re: Dart electrics

Post by A.N.Other »

I would guess that you have to determine why it wouldn’t start. First things first first, some simple tests, but before that how often has it happened often or just the once ? If its just the once then don’t stall it again so your not put in the same position.
Testing would be to get it up to temp, get the fan clipped in then simulate the same situation. If it doesn’t start then turn the fan of instantly and try to start. Do this three or four times to dispel coincidence.
Check the wiring for the fan it should be on a separate fused circuit not related to the ignition. Easiest way to tell is put your finger up a plug lead when the problem is apparent.
You may also want to check that the fuel pump is functioning properly with the fan on. Even if the filter looks OK check that the feed to both carbs is correct by taking pipes of.
Colin,
I may be slow but I’m rough as well !

User avatar
RadfordJim
Posts: 140
Joined: Tue Feb 16, 2016 10:19 am
Location: Coventry

Re: Dart electrics

Post by RadfordJim »

Hi Dave, I'm surprised when you say your engine cranked at usual speed. I've tried to start after refuelling with a hot engine and the starter would hardly turn due to the voltage drop caused by the fan surge current, the solenoid, starter and the ignition.
The fan was wired through the ignition switch and thermostat so I couldn't isolate it when starting.
I fitted a three position toggle switch (in place of the panel switch), ON via ignition and stat, ON overide direct from battery and OFF.
On my last trip the fan was running continuously and when I switched off, the ignition key was very hot. I've since fitted a relay in the fan circuit so the ignition switch now only carries the relay coil current. The supply to the fan relay is fused at 20A and the coil at 5A.
To answer your question, yes turn off the fan before engaging starter ;)
Cheers
Jim in Coventry - Home of the Daimler

Bud
Posts: 318
Joined: Fri Feb 12, 2016 9:06 pm
Location: Rochester, NY

Re: Dart electrics

Post by Bud »

Yes, isolating the new circuits with relays to keep the draw on the battery under control will help.
All that amperage draw at the same time heats the wiring and reduces battery voltages needed for the extras added.

simonp
Wise Man
Wise Man
Posts: 526
Joined: Mon Mar 07, 2016 9:59 am
Location: Birmingham

Re: Dart electrics

Post by simonp »

Had a similar problem on a MG V8 - always had to disconnect the fan. Had a few electrical issues mostly solved by adding an additional earth strap.

The SP also has earthing issues and have found that the connections around the solenoid need cleaning and checking in addition to the other items raised. There may also be an issue with the battery and charging. Also possibly that those wonderful coils might be failing - they always do far too regularly.

SimonP
Daimler SP 250 - "To feel its eager response as you open up is to know a new motoring adventure"(Sales brochure) The adventure continues!

silverdart
Posts: 285
Joined: Sat Feb 13, 2016 10:49 am
Location: West Midlands

Re: Dart electrics

Post by silverdart »

Hi All, Thank you for your comments.
I already have a relay in the circuit and at present and this is all wired through the ignition circuit I would like to keep it this way.Also as it happens, if I unplug the fan I find the car will start as normal. This leads me to believe I need to fit a separate isolation switch for the fan which I can operate if necessary.

Dave.

Bud
Posts: 318
Joined: Fri Feb 12, 2016 9:06 pm
Location: Rochester, NY

Re: Dart electrics

Post by Bud »

Dave,

Check your Grounds, clean the surfaces, make sure the trans and engine straps are in good situ.

silverdart
Posts: 285
Joined: Sat Feb 13, 2016 10:49 am
Location: West Midlands

Re: Dart electrics

Post by silverdart »

Thanks, Will do.

Dave.

User avatar
Jez
Posts: 89
Joined: Mon Feb 15, 2016 8:00 am

Re: Dart electrics

Post by Jez »

I've seen this happen a number of times and it's always due to the load from the fan causing a voltage drop, either on the supply or on the earth side, which then prevents the ignition system working properly. It's usually loose or corroded contacts, although it can also be caused by a struggling battery which can recover after a short time without load.

A cooling fan is a high load device and should always be driven through a relay. To avoid high load (and potential problems of voltage drop and overstressing existing components) the relay supply can be taken via a fused connection directly from the battery or solenoid terminals. If you want the fan to only work with the ignition on the supply for the thermostat which then drives the relay can be taken from the ignition circuit as it's current demand is minimal.

Cheers - Jez
Jez Stow
1960 Daimler Dart
and a few other toys

silverdart
Posts: 285
Joined: Sat Feb 13, 2016 10:49 am
Location: West Midlands

Re: Dart electrics

Post by silverdart »

Hi, I fitted an isolation switch and recently needed to shut down the fan to re-start the engine. Pleased to say the set up worked perfectly.
Thanks once again for all your comments.

Dave.

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