Starting a motor with a near flat battery.

skipmac said:
Also won't work with some transmissions, like hydraulics. At least the one I have.

Here's another trick. If you're stuck with two 12 V batteries that won't crank the engine but are not totally dead, connect them in series to get 24 Volts instead of 12 and it should do the trick. Reconnect back into parallel 12V configuration after it cranks. Be careful how you do this so you don't fry the alternator or other electrical stuff.
Click to expand...

This will work and is often done BUT BE VERY VERY CAREFUL NOT TO APPLY 24 VOLTS TO OTHER 12 VOLT ITEMS. The magic smoke will escape.
 
A previous boat of mine was a 60ft converted Scottish Fishing boat, with a 6 cylinder Gardner 6L3. These engines, which are 17 litre, run at 900 revs (max). Tick over is about 250rpm. It was quite easy to start the engine, if you could get the boat going about 3 or 4 knots. Each cylinder has its own decompressor. It has a mechanical gearbox, and a 49", four blade propeller. It wasn't a thing I did regularly, but it was always there, in reserve.
 
William_H said:
The idea of wiring 2 x 12v batteries in series is interesting. Not necesarily a huge advantage if any over 2 x 12v batteries in parallel. The higher initial voltage will drop hugely with the higher intitial current through the starter when in series. Once the engine starts the alternator should not be damaged. It will probably not charge as the batteries in series will recover voltage and probably be more than 14v. If not it soon will be. Some concern however for warning lights pre heaters etc before you crank the engine.
With batteries in parallel the current will be shared by the batteries so only half hence volt drop even for flat batteries will be less.
I think I would prefer to try to start using flat 12v batteries in parallel myself. it also means that they can both be charged immediately without stopping the engine.
Anyone know any better? olewilll
Click to expand...

24v (series) makes thing happen- but yes, watch frying other stuff while you are congratulating yourself on the start. Pull fuses, alternator plug first or hot wire and start with key off, possibly, depends on your confidence and the size of the emergency.

Car auctions often have a 24v starter truck battery trolley.

Here's a perfect way (TM@Nick Robinson) to start an old inertia set up.

Imagine the big terminals on the separate solenoid.
Turn on key and do all the normal start preps, heater/excess fuel/throttle etc.
Take your jumps from the second battery and connect them backwards (!), ie neg to pos, pos to starter briefly across the solenoid.
No need to turn key to 'start' watch you fingers!

would work on pre-engaged but you would need more hands... edit- no it wouldn't, when the solenoid was energised by the key, the second battery would be shorted.
 
Last edited:
William_H said:
The idea of wiring 2 x 12v batteries in series is interesting. Not necesarily a huge advantage if any over 2 x 12v batteries in parallel. The higher initial voltage will drop hugely with the higher intitial current through the starter when in series. Once the engine starts the alternator should not be damaged. It will probably not charge as the batteries in series will recover voltage and probably be more than 14v. If not it soon will be. Some concern however for warning lights pre heaters etc before you crank the engine.
With batteries in parallel the current will be shared by the batteries so only half hence volt drop even for flat batteries will be less.
I think I would prefer to try to start using flat 12v batteries in parallel myself. it also means that they can both be charged immediately without stopping the engine.
Anyone know any better? olewilll
Click to expand...

It definitely worked for me: on either battery alone the engine would not turn, in parallel the two batteries would only barely turn the cold engine, in series much faster and it started. 30 seconds to warm up engine a bit and then reverted to parallel. Everything else (not that there was much except a few lights) obviously turned off until back to normal 12v. Then JUST started on both batteries in parallel. If it hadn't I'd have run again on 24v to get the engine warmer.

It was on an old and poorly maintained ex-MOD workboat type launch on a quite remote mooring and I urgently needed to have it running. Going back ashore and finding and lugging out another battery would have taken far too long: I'd have lost at least a tide. In those days little jumper pack units did not exist.....
 
skipmac said:
I read about this trick in some article or book many years ago and filed it away in the memory banks for just in case. Then found myself stranded in the far south Bahamas with 2 very weak batteries and no one with a car or battery within 150 miles.

The engine would just barely turn over with the regular setup IE batteries wired parallel for 12V. Tried several times until it the batteries were so far down the engine wouldn't turn over at all. Hooked the batteries in series for 24V and the engine turned over faster than it did with fully charged batteries at 12V. Started immediately.

So the recommendation based on personal experience, not theory.
Click to expand...

Yes, I also did this about 47 years ago with a VW beetle engine. I'd built a beach buggy (remember them) and started off with a 6V system. OK until the first cold winter day and then I needed a 12V battery to start it. Not diesel obviously but the engine spun so rapidly it sounded as if it was producing more power than when it was actually running. I don't think I'd like to try it with my modern Yanmar unless situation was desperate.
 
Uricanejack said:
I suppose I could try this if it was cold out.
I have found if there is enough power left to turn the engine over when the compression levers are open. Let it get up to speed, close the leavers and off it goes.
Click to expand...

Once started a Transit by heating just the injector pipes when it was freezing, not the whole engine block. I used 2 lighters to heat up the pipes close to each of the injectors, moving back and forth between them until they felt pretty warm. My reasoning was that I only needed to spray warm diesel to improve chance of starting, not heat up the whole engine block. Cold oil etc. meant that it turned over fairly slowly but it did start immediately.
 
Mistroma said:
Once started a Transit by heating just the injector pipes when it was freezing, not the whole engine block. I used 2 lighters to heat up the pipes close to each of the injectors, moving back and forth between them until they felt pretty warm. My reasoning was that I only needed to spray warm diesel to improve chance of starting, not heat up the whole engine block. Cold oil etc. meant that it turned over fairly slowly but it did start immediately.
Click to expand...

Excellent tip!
 
No decompressor on a Volvo 2020D, but as I crossed Dover straight in a gale i must have accidentally kicked the engine into gear. The prop usually freewheeled with the fixed prop & when i went below I noticed the engine ticking over. I was going quite quick, i actually managed over 11knts on surfing a number of times so the prop was spinning hard. Cannot imagine doing that at 6kts.
 
Just of interest for the technically minded, when I worked in aviation we had a Gulfstream 1000 turbo prop. Now turbine engines need to be really wound up to a great speed for cooling before applying fuel and fire. A slow crank can melt the engine due to a lack of cooling air.
This machine had a normal 24volt electrical system with 2 batteries. On start up initially there was a huge current from 2 parallel batteries winding up the quite heavy turbine prop etc. (single shaft engine). As the speed of the starter increased the current falls due to back EMF. Once the sensors found the current had fallen and the engine was turning fairly well the batteries were switched in series to hit the stater with 48 volts. This higher voltage overcame the back EMF to get an even higher cranking speed before firing up. It worked well.
Perhaps this system could be used with a diesel engine by having a much greater reduction gear ratio between stater and flywheel. So firstly stater just gets the engine turning slowly so less power needed then crank speed could be increased with 24v cranking. Of course having auto operating decompression would help also. olewill just waffling good luck....
 
A crude way to help a diesel starting is letting it suck the flame of a burning newspaper through the air inlet, without an air filter.
Did it once.

Sandro
 
Sandro said:
A crude way to help a diesel starting is letting it suck the flame of a burning newspaper through the air inlet, without an air filter.
Did it once.

Sandro
Click to expand...

A burning newspaper stuffed into my engine bay ....... I'm not ready for that level of stress yet.

Sticking SWMBOs hairdryer into the air intake of my lawnmower on a cold day seems to work well so that might work with a marine diesel but I guess that if you have an electic supply you would be able to start the engine normally. :rolleyes:

Richard
 
To start a Stuart turner if it got flooded one would dry the cylinder by holding the plug over the cylinder so as the escaping gas passed the plug it ignited & burned all the fuel in the cylinder. one could then replace the plug & wind away. However one day it ignited the fuel in the carburettor drip tray which ran down onto some fuel in the bilges floating on some water & set the boat alight mid north sea. it took 2 fire extinuishers to put it out. crew abandoned the boat & jumped into the dinghy. When they came back one was p.ss.d off because I had accidentally squirted foam into his open kit bag which had his suit in.
A few years later I tried the same trick with the wife's lawnmower & burnt a 1 meter square in the lawn. I did manage to save the lawnmower, but burnt some paint off of it .
Miserable c.w got the right hump!!!!
 
I've heard of engines with no decompressor being started by wedging pennies between rocker and valve stems.
Crank it up then progressively whip the pennies out with pliers.
You have to trust there is clearance on the piston and really need the thing to go...
 
RichardS,
I agree, when I did it the motor was on a workshop bench.
If fitted on board, I would rather row all the way home.

B.t.w. I sincerely envy your age and sailing with your children as crew.

Cheers
Sandro
 
RichardS said:
Sticking SWMBOs hairdryer into the air intake of my lawnmower on a cold day seems to work well so that might work with a marine diesel but I guess that if you have an electic supply you would be able to start the engine normally. :rolleyes:

Richard
Click to expand...
Once tried to start a Range Rover by pointing a heat gun at the air intake. Only succeeded in setting fire to the paper air-cleaner element ....
 
quote "Once tried to start a Range Rover by pointing a heat gun at the air intake. Only succeeded in setting fire to the paper air-cleaner element ...."

I told "without an air filter"...

Sandro
 
Sandro said:
quote "Once tried to start a Range Rover by pointing a heat gun at the air intake. Only succeeded in setting fire to the paper air-cleaner element ...."

I told "without an air filter"...

Sandro
Click to expand...
I was aware of that, and it demonstrates that you were smarter than I was at the time I did it.
I still think it was worth telling my story, either as a cautionary tale or to allow people to feel superior.
 
Alan,
I am sorry if I gave the impression of feeling superior. Believe me I am quite the opposite. I typed that just smiling. That was the meaning of the three dots.
I would add that when I removed the air filter I was only aiming at the effectiveness of the system, far from thinking of fire danger.

Fair winds

Sandro
 
You must log in or register to reply here.

Other threads that may be of interest

N
Volvo Penta Alarm Module/Alternator Issues
Replies
1
Views
138
superheat6k
superheat6k

Share this page

Top