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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Connecting Electric Start Motor to Battery

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CateP
Navigator

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USA
108 Posts

Initially Posted - 01/28/2013 : 15:14:26

Spring project list continues.

I have a Tohatsu 9.8 electric start outboard and am not pleased with the funky wiring that exists connecting the motor to my AGM battery. I think I am on borrowed time.

Right now I have the motor wires connected to a home-made junction block. The wires are sandwiched (Bolts and washers) in with what I think are 18g wires that lead down through the aft berth. At around the mid point it looks like the 18g switches to 10g and that is what goes to the battery. I know for a fact that the 18g wire is corroded (green)and I would really like to re-wire, BUT what about that 10g wire leading to a battery connection?
Do I keep it? Seems odd to have such different gauge wires in this case.
Or do I go with another gauge wire from the junction block to the battery? (one clean connection)

Edited by - on

Bill Holcomb
Admiral

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USA
769 Posts

Response Posted - 01/29/2013 : 08:00:12

What size wire comes off the engine? I'd go with that size.
Bill Holcomb - Snickerdoodle #4839

Edited by - on

awetmore
Master Marine Consultant

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USA
1144 Posts

Response Posted - 01/29/2013 : 08:31:06

You might need to go larger than the size that comes off of the motor due to the extra length. You also need to have a fuse in the circuit.

I think the starting current for that motor is around 30A to 40A. For a 25' circuit (that is about the length from the batteries to the motor and back) you should have between 4 AWG and 8 AWG cable based on this chart:
http://bluesea.com/files/resources/newsletter/images/DC_wire_selection_chartlg.jpg

8 AWG is for 10% voltage drop (higher than ideal), 4 AWG is for 4%. You should check the actual starting current requirements with a Tohatsu dealer.

The stock starting wire on the Tohatsu 9.8 that was on my boat was only about 10' round trip and so 10 AWG would have been okay.

It is important to have a fuse that is matched to the wire, not the application. If the fuse is too large for the wire (like you use an 80A fuse) then you could start a fire if something in the circuit shorted out. If you run 25' of 8 AWG wire I'd use a 40 amp fuse. I like this type of fuse that mounts directly to the battery terminal:
http://bluesea.com/productline/overview/379
with this holder:
http://bluesea.com/productline/overview/378

Edited by - on

sweetcraft
Admiral

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USA
816 Posts

Response Posted - 01/31/2013 : 03:45:12

I used the #8 and used an rv breaker at the btry. sized to the wire. They come in different amperages. Also have a plug and socket inside the boat closer to the outboard so it can be removed without unstringing. The Forum gave me the idea of protecting from the btry, the breaker which could be reset after finding cause. My breaker has not activated so far. A fire at sea could ruin your whole day.

Edited by - on

CateP
Navigator

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USA
108 Posts

Response Posted - 02/01/2013 : 07:39:08

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by awetmore
 You might need to go larger than the size that comes off of the motor due to the extra length. You also need to have a fuse in the circuit.

I think the starting current for that motor is around 30A to 40A. For a 25' circuit (that is about the length from the batteries to the motor and back) you should have between 4 AWG and 8 AWG cable based on this chart:
http://bluesea.com/files/resources/newsletter/images/DC_wire_selection_chartlg.jpg

8 AWG is for 10% voltage drop (higher than ideal), 4 AWG is for 4%. You should check the actual starting current requirements with a Tohatsu dealer.

The stock starting wire on the Tohatsu 9.8 that was on my boat was only about 10' round trip and so 10 AWG would have been okay.

It is important to have a fuse that is matched to the wire, not the application. If the fuse is too large for the wire (like you use an 80A fuse) then you could start a fire if something in the circuit shorted out. If you run 25' of 8 AWG wire I'd use a 40 amp fuse. I like this type of fuse that mounts directly to the battery terminal:
http://bluesea.com/productline/overview/379
with this holder:
http://bluesea.com/productline/overview/378
<hr height="1" noshade id="quote"></blockquote id="quote">

This is great advice. Question about the fuse and holder. I assume this goes on the + terminal and any wire s going to the battery are attached over the screw on the fuse? Right now I have battery lugs nuts connecting the wire to the battery.

Edited by - on

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 02/01/2013 : 09:09:48

Correct. My circuit is hardwired to a waterproof trolling motor receptacle mounted on the transom with a twist-lock plug on the motor. Quick, easy and reliable.

Edited by - on

awetmore
Master Marine Consultant

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USA
1144 Posts

Response Posted - 02/01/2013 : 10:58:28

Cate: That is exactly how those fuse holders work. They make it almost trivial to add a proper fuse right at the battery.

You should also have a fuse in the circuit for every circuit that is attached directly to the battery. It's a belt and suspenders approach.

On my boat I cleaned it up quite a bit by mounting one of these very close to the battery:
http://bluesea.com/category/81/21/productline/126

All of my unswitched loads (bilge pumps, boat heater, etc) are on that fuse block. Only that block, the starter motor, and the main fuse/switch/breaker panel are connected directly to the battery. Each of those has an appropriately sized fuse that is sized to match the wiring. This fuse block is good for small loads, but too small for a starter motor.

On a Catalina 25 you might not have any unswitched loads (or might only have one or two), so a fuse in each of those loads rather than a centralized fuse box can be appropriate. On our Catalina 25 the only unswitched loads were the VHF (which should have been switched) and the starter, and each of those had an inline properly sized fuse. The important part is to have a fuse or circuit breaker on every circuit to protect from overloads. An unfused overload is very likely to result in a fire.

Both of my boats (made in the mid-80s) had a number of unsafe circuits.

Edited by - on

CateP
Navigator

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USA
108 Posts

Response Posted - 02/01/2013 : 11:27:03

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by awetmore
 Cate: That is exactly how those fuse holders work. They make it almost trivial to add a proper fuse right at the battery.

You should also have a fuse in the circuit for every circuit that is attached directly to the battery. It's a belt and suspenders approach.

On my boat I cleaned it up quite a bit by mounting one of these very close to the battery:
http://bluesea.com/category/81/21/productline/126

All of my unswitched loads (bilge pumps, boat heater, etc) are on that fuse block. Only that block, the starter motor, and the main fuse/switch/breaker panel are connected directly to the battery. Each of those has an appropriately sized fuse that is sized to match the wiring. This fuse block is good for small loads, but too small for a starter motor.

On a Catalina 25 you might not have any unswitched loads (or might only have one or two), so a fuse in each of those loads rather than a centralized fuse box can be appropriate. On our Catalina 25 the only unswitched loads were the VHF (which should have been switched) and the starter, and each of those had an inline properly sized fuse. The important part is to have a fuse or circuit breaker on every circuit to protect from overloads. An unfused overload is very likely to result in a fire.

Both of my boats (made in the mid-80s) had a number of unsafe circuits.
<hr height="1" noshade id="quote"></blockquote id="quote">

Hmm. Now I am getting concerned that I've got a fire hazard just waiting to happen on board. I am not able to check things out right now, but as I recall there are several wires hooked up to the battery. I also replaced the electric panel when I bought the boat and worked with an electrician to hook that up.

I am assuming anything that has a switch off would not need fuse inline?

So is the bottom line here that I should check every wire leading to the + terminal on my battery to make sure there is a fuse on it? Wondering how I would know what size fuse to put inline and how I do it.

Does that BlueSea fuse box work in conjunction with the electrical panel?

Edited by - on

awetmore
Master Marine Consultant

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USA
1144 Posts

Response Posted - 02/01/2013 : 15:32:18

If you replaced the electrical panel then you likely have switch breakers, not switches. With those you don't require a fuse because the breaker will trip. If you look at the back of the panel it is easy to identify them, circuit breakers will have a roughly 1/2" x 2" x 1.5" box while switches are much much smaller. On our 1984 C-25 the stock panel had switches with fuses next to each one.

You should still need a fuse on the unswitched circuits (or you can move them to a breaker). There should also be a master fuse on the wire going from the battery to the circuit breaker panel. That protects you from any issues at the breaker panel itself.

Don Casey has a good book on sailboat electrics that goes into all of this in detail.

Edited by - on

awetmore
Master Marine Consultant

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USA
1144 Posts

Response Posted - 02/01/2013 : 15:33:06

I'll add that I found it useful to map out all of the circuits on our boat and to indicate where the fuses and/or breakers are. I don't know if I still have a copy of it, but if I can find then I'll post it.

Edited by - on

Voyager
Master Marine Consultant

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USA
5378 Posts

Response Posted - 02/01/2013 : 21:36:59

Yes But.....
Any cable that is connected to the + terminal of the battery should have a fuse in line within a few inches of the battery terminal.
A wire, especially a #6, #8, #10 or #12 AWG can carry an enormous amount of current and power producing a great deal of heat, and a short anywhere between the battery and the fuse or breaker will cause a fire quickly.
Don't kid yourself, fiberglass can and will burn very vigorously, especially when accelerated by an electrical fire. Many boats that have electrical fires burn down to waterline.

Edited by - Voyager on 02/01/2013 21:38:05

CateP
Navigator

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USA
108 Posts

Response Posted - 02/04/2013 : 06:43:44

Thanks everyone for the VERY helpful advice. Sometimes the Q&A format is exactly what's needed, but I also have Don Casey's book on sailboat electronics.I think it's time to dust it off and read it again.

The good news out of all this is that I'm going to do a careful survey of my electronics now that I have the time this spring and am not dealing with major issues such as storm repair and transporting the boat through 5 states

Edited by - on

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