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Hard Start

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JSabah
Posts: 118
Joined: Mon Feb 15, 2016 9:27 pm
Location: Los Angeles

Hard Start

Post by JSabah »

When I first start up my SP250 (with original but rebuilt generator), I have no problems. If it has been a month, week or day, it fires right up. My problem is that after driving it (city driving), if I return to the car within 1/2 hour or so, it barely wants to turn over as if the battery is low. My generator/dynamo was rebuilt as well as my gauges when I restored the car about 4 years ago (also when I installed a new battery). I converted to a volt meter and when at idle it reads between 13 & 13.5 volts. When underway, it reads at just over 14v. After I stop and turn the car off, it I immediately turn on the gauges only, it reads 12v....and goes up over time. Any thoughts? I'm hoping it is a simple as a faulty/old battery.
Thank you, Josh
Sp250, Sunbeam Tiger, MGTD, Jensen Interceptor conv, Jensen Interceptor Coupe', '49 Plymouth Woody and now a '65 Jensen CV8 Mk3 LHD

Sydsmith
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Location: Aberystwyth Wales

Re: Hard Start

Post by Sydsmith »

Josh. First things first, a good 12 volt battery when fully charged should show 13.5 volts and in order to charge the battery fully, the generator needs to produce more than 13.5 volts, typically 14 volts. So for start one you have the correct readings, however when you start again, it drops to 12volts, that would tend to suggest a poor earth or ground connection from the battery, rather than a duff battery.

I had a similar problem when I first bought my SP and it turned out to be the earth from the chassis to the gearbox housing and not the negative lead from the battery to the chassis. (Mine is positive earth)

Good modern batteries tend to last 6-10 years, my Bosch battery is now 10 years old and still going strong, so I doubt the battery is at fault, but any good battery supplier should be able to test it for you with a special battery volt meter with a shunt/load resistor attached to give a true reading of the battery condition.

For a battery to lose so much voltage in such a short time any load would have to be very high, which would produce heat and probably smoke, so my money is on a faulty high resistance earth connection.

One other possibility is timing, if the ignition is too far advanced the engine will try to start against a cylinder being fired at the wrong time and that will produce resistance. In the old days of starting handles if an engine were too far advanced it would kick back and if you had your thumb wrapped round the handle it would give you a very nasty whack. Syd

JSabah
Posts: 118
Joined: Mon Feb 15, 2016 9:27 pm
Location: Los Angeles

Re: Hard Start

Post by JSabah »

Thank you. I didn't think that a bad earth would drain the battery (and would think that a bad ground would also give difficulty on a cold start) .... I should have taken my own advice. Whenever somebody comments on how difficult owning a British cars are, I always answer "Naw, its ALWAYS a bad ground". Thanks, Ill have a look, clean and tighten the contacts. Its been about 4 years and only 800 miles so it is probably time to see what has shaken loose....
Sp250, Sunbeam Tiger, MGTD, Jensen Interceptor conv, Jensen Interceptor Coupe', '49 Plymouth Woody and now a '65 Jensen CV8 Mk3 LHD

KV8
Posts: 304
Joined: Sun Mar 06, 2016 7:05 pm
Location: Cambridgeshire

Re: Hard Start

Post by KV8 »

Sydsmith wrote: Mon Nov 18, 2019 8:37 pm Josh. First things first, a good 12 volt battery when fully charged should show 13.5 volts
I am sorry but that is incorrect. A fully charged battery will read 12.6 to 12.8 volts

Please see This Site and many others.

A battery may show a higher voltage for a very short time after disconnection from a charger or car charging circuit but will rapidly fall to 12.6 V

H

russcarpenter
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Joined: Sat Feb 13, 2016 5:26 pm
Location: Guildford
Contact:

Re: Hard Start

Post by russcarpenter »

you might take a look at the starter motor I first came across this problem when I fitted a V8 engine into my Triumph tow car back in the late seventies, evry time I went to fill up after a run came to start up your symptoms. changed the starter and no more problems, stripped the starter and could not find any trouble but when tested it always dropped out when we heated it engine temperature.

Sydsmith
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Joined: Sun Feb 14, 2016 11:15 pm
Location: Aberystwyth Wales

Re: Hard Start

Post by Sydsmith »

KV8, I won't argue because you are correct, but, I was explaining to Josh what he was seeing on his volt meter was correct, without muddying the water for him by going into too much detail.

Auto electrics are an illogical art to many. After all, where is the logic , he has a 12 volt battery it say so on the side of a battery, what Josh is seeing on his volt meter does not make any sense.

I know very clever and intelligent mechanics that are mystified the moment they are confronted with electrics. Syd

Ian Slade
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Location: Sevilla Spain

Re: Hard Start

Post by Ian Slade »

It's very simple, it's a 12v battery as that is the easiest way to describe it, it's not 11v or 13v it may overchage to 13v but actually it is 6 times 2.2v each cell beeing connected in series, that makes it a 13.2v battery theoretically but it cannot hold that charge due to the battery's internal resistance which reduces the voltage to about 12.4 to 12.8 volts depending on its construction, i.e the number of plates and materials used, the old simple lead acid has long gone, there are all sorts of chemical additions to extend life and number of charges.
Generally a quick check as to whether a battery is good or nor is simply to turn on the headlights and connect a voltmeter/multimeter a ross the terminals, the voltage on a fully charged healthy battery should not drop below 12.4v in 15 minutes, if a cell has failed it will rapidly drop to below 11v
Owner since the 70's, Genghis is slightly to my left.

Petelang
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Re: Hard Start

Post by Petelang »

From what you describe I think it suggests a battery fault. If you have cell caps, remove each and examine if any look blackened like soot, any loss of electrolyte in any particular cell. Any smell of eggs around it when it's being charged. If you have a hydrometer, draw off a sample of the electrolyte which should be clear. Do this after you have got it hot from a run. If it comes up with any contamination within it, Red or black, will indicate cell plates breaking up. If any one cell starts gassing when on charge may indicate a shorted cell plate which will reduce the voltage.
Easiest option is visit local battery supplier and they can do a cold start performance test which will tell if it's performing correctly. They usually offer this free.
A cell which has stood for a long time and the fluid level drops as it is absorbed back into the plates exposes the tops of plates which then become sulphated and this can short out plates. It was the greatest destroyer of batteries left for periods uncharged and cannot be undone.

The other possibility is the starter, when hot, with broken down insulation of field coils leading to greatly reduced performance.
Peter
Peter Langridge
Cloud Nine Classic Weddings, Nottingham.

Ian Slade
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Re: Hard Start

Post by Ian Slade »

The field coils on a starter motor are almost short circuit, it is a series wound motor, if anything the cause would be a high resistance connection when hot. Batteries today are often sealed and the individual cells are not accessable, the headlight test is as good as any test for a quick assessment, there are a few intelligent chargers about that can pulse charge the battery and partially repair damaged cells for an extended life.
Owner since the 70's, Genghis is slightly to my left.

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