Good idea or bad idea- DIY jumper cables for a Mercedes

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Hey, everyone. I hope everybody is safe during these tough times.

My dad's w210 cranks, but won't start. It started to crank a little more everytime we'd give it time and turn the key, but we were scared of breaking something so we stopped and decided to go out and buy jumper cables. But we couldn't find any longer than two meters here in India, so my dad was kinda thinking about making our own- we could find some thick gauge wires and get alligator clips and make it ourselves, at least the standard 12 feet length... Something I wouldn't be concerned about making and using on my Hyundai, but I don't know how this would affect the Merc's electronics. Some of the reviews say that the jumper cables are copper coated aluminium; I don't know if that's a good thing or if a full copper wire is better. Does anybody have some advice or experience with this scenario? Thanks in advance. Stay safe.

P.S: The wire quality will be good, if that's a concern.
 
Hi. Are you wanting to do this just to crank longer? You could burn the starter motor out if you continue to crank it. I would try and resolve the starting issue. What engine does it have?
 
Hi. Are you wanting to do this just to crank longer? You could burn the starter motor out if you continue to crank it. I would try and resolve the starting issue. What engine does it have?
Really appreciate the speedy reply, bob6600. No, I don't want to do this just to crank longer. I just observed that, and thought that it might be useful information; nothing more. It's the 2.2 liter cdi version(143hp). The thing hadn't been started for at least two weeks, so we thought that might be the issue. Hence the jumper cable query. I should've included that in the original post. Another piece of information that might be worth something- sometimes, the car just doesn't want to start, and by that I mean it won't even crank right when we need to go somewhere. Then, a day or two later it inexplicably starts up on the first turn of the key. This happened with the new battery, too.
 
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Full copper jumper leads are better, they are only using aluminium because it's cheaper. If you are going to make DIY jump leads then use a minimum 6 mm2 cable and keep the ;length as short as is practical.

Your Mercedes owners manual will contain some instructions and cautions on using jump leads.
 
If the car cranks for reasonable time it is unlikely to be the battery and the jump leads to another battery won’t h

as others have posted it is possible an EIS or crank sensor issue

first step is to check if you have both a spark and fuel delivery
 
I’d suggest taking the battery out of the car and charging it .

if the battery is more than five years old , I’d suggest you need a new battery. You could ‘borrow’ a known good battery out of another car to test this .
 
A W210 is quite old so it's worth checking the earth strap between engine and chassis, it should be somewhere around the rear of the engine or bellhousing area. The connections can corrode and cause all sorts of strangeness including bad starting.
 
Indeed , or the battery earth strap ; in a W210 , at least ones I've seen , the battery is under the back seat .
 
0 gauge audio power cable will work too. OP not sure where you are, but someone (myself included if you're near by) would be happy to lend you a trickle battery charger or some thick gauge audio cable 👍🏽
 
There's no specific limit on tne jump leads' length, but on a general note, the longer the cable the thicker is should be, or it will overheat.

In layman's tetms, when thinner/longer cable will overheat, it might melt the insulation, but even if it doesn't do that, heat is wasted electric energy, so the hotter the cable the less powerful the cranking.

In short... keep the cable as thick and short as practically possible.

And don't forget that you need a solid good large-area contact between the ends of the cable and the alligator clamps - if the contact isn't sufficient, this will cause a bottleneck where electricity gets converted to heat instead of getting to the starter motor.

And last, start the car from an external battery that is not fitted in another vehicle - or you could damage either car's electronics (from SAM etc).

Or..... use a trickle-charger with a long extension cord to the nearest wall outlet?
 
MarkJay is spot on, a lower cross section cable will offer more resistance as it heats up with the high current cranking load. You probably need a cable with at least 20mm cross section area for anything over 2m. Get the best croc clips you can with strong springs and preferably insulated. TBH for the time and cost you will spend making some, I'd just get some 3 - 3.5m ones mail order to you in India. They are available.

 
I’ve got some nice 5m Sealey ones. 35mm2 and pretty heavy fittings to match. Someone must be importing Sealey equipment.
 
MarkJay is spot on, a lower cross section cable will offer more resistance as it heats up with the high current cranking load. You probably need a cable with at least 20mm cross section area for anything over 2m. Get the best croc clips you can with strong springs and preferably insulated. TBH for the time and cost you will spend making some, I'd just get some 3 - 3.5m ones mail order to you in India. They are available.

Thanks for the info, Shadychris and MarkJay. We got the whole thing done in about 25 quid, if not a little less. It's a 35mm² copper wire and about 10 feet in length, so that should suffice, hopefully.
 
I’d suggest taking the battery out of the car and charging it .

if the battery is more than five years old , I’d suggest you need a new battery. You could ‘borrow’ a known good battery out of another car to test this .
The battery is not even a year old, so that should rule that out. But the battery did go dead, though🤔 I know that it hadn't been started for a few weeks, but I couldn't even get the doors to unlock through the key fob. And the key fob batteries were fine.
 

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