Using Morris to jump-start modern car

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Edward1949
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Using Morris to jump-start modern car

Postby Edward1949 » Sun Apr 28, 2019 4:15 pm

Is there any technical objection to this? My Minor is in original specification. Could the dynamo/control box be adversely affected?

oliver90owner
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Re: Using Morris to jump-start modern car

Postby oliver90owner » Sun Apr 28, 2019 5:44 pm

The car starts itself without damaging the voltage control box, doesn't it?

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les
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Re: Using Morris to jump-start modern car

Postby les » Sun Apr 28, 2019 6:03 pm

To answer your question, you should have no problems doing this.


myoldjalopy
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Re: Using Morris to jump-start modern car

Postby myoldjalopy » Sun Apr 28, 2019 6:37 pm

Depending on what the 'modern' is, you may find that your dynamo doesn't give out enough charge for a big beast with a big battery....

panky
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Re: Using Morris to jump-start modern car

Postby panky » Sun Apr 28, 2019 10:49 pm

Is your car negative earth?
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Edward1949
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Re: Using Morris to jump-start modern car

Postby Edward1949 » Mon Apr 29, 2019 12:07 am

panky wrote:
Sun Apr 28, 2019 10:49 pm
Is your car negative earth?
Positive, as per original spec. I don’t think this could have any relevance (unless I got my polarities crossed :o ).
My concern is whether the massive initial demand of a starter motor in a car with an exhausted battery (which must be more than even an alternator can produce) could have some adverse effect on my traditional dynamo setup.

simmitc
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Re: Using Morris to jump-start modern car

Postby simmitc » Mon Apr 29, 2019 10:00 am

Although you will be attempting to charge your own battery and the modern battery, the power for starting the car will be drawn from your battery, not just the dynamo; and should not cause any problems. As yo note, just make sure that the polarity is observed when connecting jump leads.

oliver90owner
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Re: Using Morris to jump-start modern car

Postby oliver90owner » Wed May 01, 2019 11:24 pm

Edward1949 wrote:
Mon Apr 29, 2019 12:07 am
panky wrote:
Sun Apr 28, 2019 10:49 pm
Is your car negative earth?
Positive, as per original spec. I don’t think this could have any relevance (unless I got my polarities crossed :o ).
My concern is whether the massive initial demand of a starter motor in a car with an exhausted battery (which must be more than even an alternator can produce) could have some adverse effect on my traditional dynamo setup.
How many have battery chargers capable of more than 20 Amps?. OK, I, for one, do. A 20A charger will charge most batteries from stone dead, given time (~2 hours at full charge into a 40Ah battery) - and anyway, the question is just to start the engine, not recharge an exhausted battery.

Work it out - if the engine will start, when cranked, and the starter draws 200A the capacity taken from the battery is only 180 A (assuming the jump start vehicle is running fast enough to produce full dynamo output) the battery would be discharging at only 4.5C for a 40 Amp hour battery, so would last over 12 minutes before being fully discharged! That is what lead acid accumulators are for. 200A at 12 volts is a little over 3HP. A Moggie starter motor is what? 1.5HP?

There is no real difference between a bendix and pre-engaged starter, other than that the starter gear is engaged with the flywheel before motive power is applied in the latter case. Many Minors have a solenoid, after all.

Another thought train is: What is the capacity of the battery on modern cars? Not so much different than a Minor battery, I would suggest?

What is a jump start really? Simply using a separate, external power source instead of the installed battery.

Bowie69
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Re: Using Morris to jump-start modern car

Postby Bowie69 » Thu May 02, 2019 11:33 pm

Just to throw a bit of caution in, I have myself jump started a modern vehicle, and in the process.own the airbag ecu....

You may not hurt your car, but beware the other one!


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