Does anyone know about how many amps a Universal M25 diesel starter uses? I want to replace my batttery cables and would like to size the wire as needed.
Universal M25 Diesel Starter
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IMHO, I used 2awg with that engine on a Catalina 30. I would consider that a minimum. Bigger is better. If I did it again, I would use 1/0.
Mark Alexander
Catalina 350
Catalina 30
Mark Alexander
Catalina 350
Catalina 30
I've been using the stock #4 wire that was installed on my boat in 1986. I've had the boat since 1998. While the current draw is around 150 amps (measured by Maine Sail in one of his great posts and most likely on his website) it is for a very short duration. #2 is overkill, #4 is a tad too small (but works) and they don't make a #3!!! 
The most important thing you can do is to check the connections, especially the main engine ground on the bell housing. Our C34 Critical Upgrades page has a lot of M25 series engine info, applicable to other boats and sizes, too. http://c34.org/bbs/index.php/topic,5078.0.html If you click on C34 Tech wiki, you'll find tons of other engine info.
You mentioned "replacing my battery cables." From where to where? If from the house bank to the 1-2-B switch, the oem #4 is still just fine, 'cuz you're never gonna be pulling any load larger than 15 to 20 amps anyway even with all your interior lights. OTOH, I have a combined inverter/charger, and it requires 2/0 wiring from the PDP to the I/C. I use #2 wiring from the PDP to the other house individual batteries. My high output alternator has #2 from the alternator to the house bank.
Not knowing what you have on your boat makes answering wiring questions highly difficult.
The most important thing you can do is to check the connections, especially the main engine ground on the bell housing. Our C34 Critical Upgrades page has a lot of M25 series engine info, applicable to other boats and sizes, too. http://c34.org/bbs/index.php/topic,5078.0.html If you click on C34 Tech wiki, you'll find tons of other engine info.
You mentioned "replacing my battery cables." From where to where? If from the house bank to the 1-2-B switch, the oem #4 is still just fine, 'cuz you're never gonna be pulling any load larger than 15 to 20 amps anyway even with all your interior lights. OTOH, I have a combined inverter/charger, and it requires 2/0 wiring from the PDP to the I/C. I use #2 wiring from the PDP to the other house individual batteries. My high output alternator has #2 from the alternator to the house bank.
Not knowing what you have on your boat makes answering wiring questions highly difficult.
Stu,I've been using the stock #4 wire that was installed on my boat in 1986. I've had the boat since 1998. While the current draw is around 150 amps (measured by Maine Sail in one of his great posts and most likely on his website) it is for a very short duration. #2 is overkill, #4 is a tad too small (but works) and they don't make a #3!!!
Install some 1/0 and then tell me 2GA is overkill..
Done 5 battery cable re-wires this spring alone and every owner swears they have a new starter and the engine just "jumps" to life...I had the opportunity to be at the Landing School, one of the finest boat building schools in the country, on the day the systems instructor was having the students swap out different sized battery cables for starting engines. Hearing the difference in the way the engines started was simply amazing.
Good connections are a must, and can very often be a cause of voltage drop, but with #4 you really should have everything else at 110%..
We can't forget that there are many, many boaters who start off the house bank and this bank still may need to be used in an emergency to start the engine. #4 will start the motor but 1/0 or 1GA will start it much more efficiently. When the engines "jump to life" the starter see's less load for a shorter period of time.
Catalina finally saw the light on battery cable and our 2005 C-310 shipped from the factory with 1/0 battery wire on a Universal M-25 XPB. 1/0 wire is the spec for it on Catalina's electrical schematic for the C-310 W/ Universal M-25....
If starting new, and replacing the battery cables, I'd spend the money to go to 1/0 or at least 1GA. The difference between it and 4GA noticeable..
Universals requirement for the M-25 is:
4 Ft. Wire = 2GA
5 Ft. Wire = 1GA
7 Ft. Wire = 1/0
9 Ft. Wire = 2/0
11 Ft. Wire = 3/0
14 Ft. Wire = 4/0
This is the wire length along the conductor not the "as the crow flies" distance.
I have seen in the engine compartment batteries with the switch right next to it that had more than 6 feet of wire length to the switch and back to the starter. You also can't forget the ground wire length as your starter circuit is a circular circuit from the battery to the starter and back to the battery.
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