Start motor current

RussHaley · 10 June 2002, 12:32

Does any one know the minimum ampage required for electric cable to a 55hp mariner?

It must be based on the current that the starter motor draws, but I haven't got a clue what that is. The battery cables we've got are far too short to enable the batteries to be positioned sensibly, so we need to make up some new ones.

Any help would be great.

Russ

Rene · 10 June 2002, 15:30

Hi

It's not only the current that's a issue here. It's also something to do with how long the cable's need to be....

But I think I would go for something like 15 mm2. This should do the trick. If it's to small, the cable will get warm when you try to start the engine, or the engine won't start and the cable may start to burn.

Don't put the starter cable in the same tube as your fuel line.

Regards
Rene

Scubakid · 10 June 2002, 18:09

Russ

I would be happy to give you a hand if you need it, How far is it from the outboard to the batts ? Let me know if yo need a hand.

John

Ribald · 10 June 2002, 20:21

Depending on which engine you have the starting current under load is as follows: (from workshop manual)

55HP Mariner 2-stroke = 125 amps

50HP 4-stroke = 174 amps

The only reference to cable size I can find refers to a battery cable of 5/16" which is from the 2-stroke manual which, being American units may refer to the diameter of the cable.

Hope this helps.

Garygee · 10 June 2002, 21:57

Hi Russ

As far as starter cables go, if your unsure go bigger as going bigger will cause no problems, going smaller will cause loads of problems.

A good source of cheap heavy cables is welding cables. You can get these by the meter from engineering supplies, only problem is they are only available in black.

Regards Gary

batfalcon · 11 June 2002, 10:43

I agree with Gary on this one. Welding cables are just fine for the job. They are for 100 Volt range made, rubber sheathed and flexible. You can use a red heat shrinked sheath at the ends of the possitive cable, so there will never be a mix on the polarity.

RussHaley · 11 June 2002, 14:34

Thanks for the responses. Unfortunately the manual (Seloc)
doesn't list the starting current. On the basis that it is 125 amp I will get 170 amp cables because these build in a much bigger margin than the 135 amp cables that my supplier also does and more than 170 amp gets expensive.

The cable length will be around 5.5m, which is about 17.5 feet.

The boat has twin Mariner 55s (1988 2 stroke) and I would like to save money by having one positive cable and one negative going from the batteries to one engine, then a short length of cable going from the first to the second engine. On the basis that only 1
engine will be started at a time is this a reasonable setup?

jools · 11 June 2002, 14:56

I suppose it depends why you have 2 engines!!

One of the reasons for having 2 engines is that you have redundancy. The Rib that I used to use that had twin engines also had 2 batteries - one for each engine.

I'm sure that your solution would work - but how much is a second battery and a length of cable compared to the cost of the boat and twin engines? - and your safety

Some twin engine setups also go for seperate fuel supplies/tanks to prevent contaminated fuel affecting both engines.

Jools (One engine)

Garygee · 11 June 2002, 15:01

Hi Russ

From a starting point of view yes, but as both engines will be trying to charge the battery and there may be slight diferences between the alternator voltages, not sure if a good idea form this point of view.

I think you may need a charge splitter, but I would talk to someone who knows more about twin instalations.

If i was doing it I would have two batteries and two cables.
the main reason why most people go for two outboards is safety.
On one battery if it goes flat you loose both outboards.

Regards Gary

Scubakid · 11 June 2002, 16:39

Hi

using two cables is a NO NO this will screw the charging and may damage the alternators. You can get away with three cables as you could use a common ground cable (normaly the negative). I would go for a complete twin system as it only requires one more length of cable than the three cable system as you still need two batts.

John

Garygee · 11 June 2002, 16:52

Hi John

When i say two cables I mean two complete pairs, i.e one + & -ve for each engine, making four cables in total and not two in total

Regards Gary (clear as mud again) Greenwood