Wiring 2 marine batteries in series woops

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Marinaman

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Hi guys,

So I seen online that if you connect to batteries in series (+ to - and - to +) you double the voltage so two 12v batteries becomes 24v.

So I tried to do this with a 800MCA battery and a 1000MCA battery (which was a little drained) so my engine would get enough voltage to start.

As soon as I placed the last jump lead there was a massive spark and the positive terminal on the 800MCA battery melted..

What went wrong here? does anyone know?
 
Marinaman said:
Hi guys,

So I seen online that if you connect to batteries in series (+ to - and - to
Click to expand...
<slow motion> Stoooooooopppppp,/slow motion>
+) you double the voltage so two 12v batteries becomes 24v.

So I tried to do this with a 800MCA battery and a 1000MCA battery (which was a little drained) so my engine would get enough voltage to start.

As soon as I placed the last jump lead there was a massive spark and the positive terminal on the 800MCA battery melted..

What went wrong here? does anyone know?
Click to expand...

Ok, so what you want (from the bottom up) is:
-ve to boat to -ve of batt1
+ve of batt 1 to -ve of batt 2
+ve of batt 2 to +ve to boat.

If, on the other hand you connect batt2 +ve to batt1 -ve you have a niceley short circuited 24V lead acid battery capable of throwing many hundreds of amps. That, for a poxy little battery terminal is a bit beyond welding, more like a plasma arc cutter
 
Dougal Tolan said:
<slow motion> Stoooooooopppppp,/slow motion>

Ok, so what you want (from the bottom up) is:
-ve to boat to -ve of batt1
+ve of batt 1 to -ve of batt 2
+ve of batt 2 to +ve to boat.

If, on the other hand you connect batt2 +ve to batt1 -ve you have a niceley short circuited 24V lead acid battery capable of throwing many hundreds of amps. That, for a poxy little battery terminal is a bit beyond welding, more like a plasma arc cutter
Click to expand...

Yeah that sounds about right, it was like half the terminal was spiced off! well won't be making that mistake again! :rolleyes:

Do you think the batteries are still good?
 
You have shorted the two batteries. It should hsve been + - + - with the leads taken from + of first battery and - of second battery. Although there was one engine (Ford Waterlota Sea Panther) which used a 24 volt starting set up on a 12 volt starter motor, I would never risk what you have tried not to mention you could have been blinded by molten metal from the spark. You are a very lucky man.
 
Marinaman said:
Yeah that sounds about right, it was like half the terminal was spiced off! well won't be making that mistake again! :rolleyes:

Do you think the batteries are still good?
Click to expand...

They might well be fine, they love that kind of draw (not too much worse than a truck starter motor). What would be important to them is get some charge back in.

But, beware. Its important that once the engine starts one stays connected to the alternator else that will go pop.
So, full method:
batt 1 leave connected as usual
disconnect +ve and -ve of batt 2
batt 2 connect -ve to batt 1+ve
disconnect +ve and control to starter motor
connect starter motor +ve to batt2 +ve
dab starter motor control +ve to batt2 +ve (this will spark a lot too, dont touch the lead terminal, use any part of the other wire instead)
 
XPS said:
What voltage is your engine 12v ?? If so then there is your problem
Click to expand...

I didn't try start the engine, I basically had one battery connected to the engine, got some jumper cables and hooked them up to the battery over the connectors then to the opposite terminals on the other battery, the last connection being the positive terminal on the extra battery, once it touched there was massive spark, moved the jumper cable clip away and half the terminal was gone with metal shards everywhere!
 
What you did was create a massive high amp short across the batteries , I hope for your sake and the surrounding boats you are insured, if not then move your boat away from others.

It's Amps that crank and engine into life via the starter motor not volts unles of course your specified 24 volt start in which case you do need 2 12 volt batteries wired correctly to start the engine.

I think you need serious professional help before your making an insurance claim.
 
volvopaul said:
What you did was create a massive high amp short across the batteries , I hope for your sake and the surrounding boats you are insured, if not then move your boat away from others.

It's Amps that crank and engine into life via the starter motor not volts unles of course your specified 24 volt start in which case you do need 2 12 volt batteries wired correctly to start the engine.

I think you need serious professional help before your making an insurance claim.
Click to expand...

Ok so, this was in my driveway, and all thats damaged is the battery terminal, unless your saying I fried my engine? It is a 12v mercury sportjet 175..
 
volvopaul said:
Probably fried the alternator too as the rectifier won't like 24 volts thrown at it.
Click to expand...

The rectifier wont give a damn about 24V on its output, thats what diodes do, block reverse volts. The field coil might have had something to say if any volts had actually got down the wires, very unlikely since the batteries were too busy arguing about whether the +12V to boat was 0V or 24V. And it sounds like the +12 to boat wasnt connected yet anyway.
 
gordmac said:
24V starting on a 12V system used to be common on rally cars.
Click to expand...

I did this way back in the 80s , got through a few starters though and wire it wrong and see smoke from the alternator.
No one wires rally cars like this anymore, my BDG has geared starter and Dry cell battery with plenty of go in it and weighs nothing.
 
In 1993 my London - Sydney Escort RS1600 had a 8 or 9 volt starter motor using a 12 volt battery. I had someone, (can not remember who) build the starter specially for the purpose,

Spun up very quickly and always started instantly, even after 15,000 very hard miles.

Graham
 
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