yanmar alternator wiring....help! - SailNet Community

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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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Old 01-04-2011
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yanmar alternator wiring....help!

I am trying to replace the alternator on my qm20 yanmar ...it was missing when i got the boat, so i dont know how it was wired....
here is what i can tell so far...it has three wires at the location,a heavy black that goes to motor bolt for ground. a heavy red that is battery positive. a yellow small gauge wire with a red stripe...maybe the tach trigger as far as i can tell.....
plus ...nearby is also a red wire w/black stripe small gauge with a disconnect connector ....the second part is missing....but it does have 12 volts with the key on......i am thinking this is the idiot light wire ...but the light doesnt appear to work.....
next ....the new alternator ( came with the boat) is a 105 amp, it has a four wire plug connector, i was able to buy a new pig tail to fit it.
the wires are labled as follows....left to right.....P ...tach ? next is ..L ...idiot lamp ?.....next is F with what looks to be an I above it....this one i have no clue ......and focus of my problem....is it simply not needed? .....or is it an ignition lead ? or is the F for field or something else?the last wire is battery pos....it goes back to the main positive post on the alternator...
the regulator is internal ,if that matters any.....does anyone have a wiring diagram or know how these are wired....i dont want to fry the alternator by wiring it wrong ( i have done that before)..not a pretty sight to have smoke comming from a brand new ( and expensive ) part.....
I hope this is enough information , its all i can come up with.....thanks in advance....... Ron
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Old 01-04-2011
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Ron, I don't know what you've got, but one wire may be a voltage sense lead. that goes from the alternator to the one battery, so the alternator can monitor battery voltage and regulate itself. On some systems, the sense lead is tied back right into the alternator output (which defeats the purpose) because the boat has 2 batteries and it costs more to switch the sense lead when you switch batteries. If you bypass it, that's called a "one wire" installation versus a conventional "three wire", some boats are set up that way because it is cheap.
You don't have to set it up the way the maker did, there ARE options. But you do need to make sure of what each wire is, preferably from a schematic confirmed by tracing them out to make sure someone didn't monkey with them. Maybe someone in the forum has the same make boat you do--and can comment on how it was set up.
An idiot lamp is usually connected to the "field" wire, which supplies twelve volts to "excite" the alternator and start it up. On a "1 wire" system that's usually tied back as well, with the side effect that the alternator doesn't fire up until a certain RPM is reached, often meaning you need to "goose it" to get it started.
The voltage sense lead can be critical--if it is not connected to anything, the regulator says "MORE POWER!" and often goes to 17 volts, quickly frying everything. So...take your time, make sure of what everything really is, not just what it is supposed to be.
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Old 01-04-2011
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Here's a link to a free download of the "12 Volt Doctor's Alternator Book", an excellent resource to have. Everything you wanted to know about alternators and easy to understand as well as all the different wiring configurations.
http://www.greenenergywindturbine.co...ndbook_ocr.pdf
It will help.
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Old 01-04-2011
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Quote:
Originally Posted by twisted23 View Post
I am trying to replace the alternator on my qm20 yanmar ...it was missing when i got the boat, so i dont know how it was wired....
here is what i can tell so far...it has three wires at the location,a heavy black that goes to motor bolt for ground. a heavy red that is battery positive. a yellow small gauge wire with a red stripe...maybe the tach trigger as far as i can tell.....
plus ...nearby is also a red wire w/black stripe small gauge with a disconnect connector ....the second part is missing....but it does have 12 volts with the key on......i am thinking this is the idiot light wire ...but the light doesnt appear to work.....
next ....the new alternator ( came with the boat) is a 105 amp, it has a four wire plug connector, i was able to buy a new pig tail to fit it.
the wires are labled as follows....left to right.....P ...tach ? next is ..L ...idiot lamp ?.....next is F with what looks to be an I above it....this one i have no clue ......and focus of my problem....is it simply not needed? .....or is it an ignition lead ? or is the F for field or something else?the last wire is battery pos....it goes back to the main positive post on the alternator...
the regulator is internal ,if that matters any.....does anyone have a wiring diagram or know how these are wired....i dont want to fry the alternator by wiring it wrong ( i have done that before)..not a pretty sight to have smoke comming from a brand new ( and expensive ) part.....
I hope this is enough information , its all i can come up with.....thanks in advance....... Ron
Yanmar / Hitachi alts often have the following wiring terminals but some had internal regulators and some external and some had different terminal designations. An alternator model # would really help..

This is what an LR155-4 has:

B = Battery +
E = Battery -
R = Tach
L = Charge Lamp

An LR-135-31 lacks the R terminal.
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Old 01-04-2011
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Does anyone else have a concern with putting a 105 amp alternator on a 20hp engine? Assuming the batteries get rundown and the alternator is trying to put out big amperage while one is trying to motor someplace, I would think it would be very easy to overload the powerplant. I upgraded from the factory original Hitachi 35 amp alternator when it died to "only" a 65 amp on my QM15 and wouldn't want anything bigger. Maine Sail and others can probably provide some data on the parasitic drag in HP of larger amperage alternators when under full load.
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Old 01-04-2011
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These sketches may help you: Alternator Regulator Wiring Diagrams

Our old alternator was case grounded so the ground wire didn't show on the first sketch. The following diagrams on that link show the connections for our external regulator, a Balmar MC612. All the wiring is identified.

Unless you want to buy a book, I recommend visiting Balmar's excellent website Welcome to Balmar DC Charging Solutions. Look at their manuals for regulators and they'll show the wiring.

Since two of the four wires are pretty clear (red output and black ground) the others are for the ignition, field and tach.

The Balmar manuals should better familiarize you with the uses.

Maine Sail's question is very apt.
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FarCry
An alternator uses about 1 hp/25 amps output. 105 amps is about max for a single belt according to Balmar and others. Right at the limit all around but workable.
It could be wired so it can be switched off when max power is needed for propulsion or it could be installed with a regulator that allows the output to be dialed back to say 80% - that way it would run cooler as well.
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the boat is a 1978 endeavour 32 , the alternator model # is; 20-182-11-1
lester 7973n
serial. 01.9b2
12v
105a
that is all i have on it....

does this sound reasonable ........my 4th wire on the pigtail is a heavy red wire.....the alternator is marked S in this location.....and the wire does return to the battery positive post on the back of the alternator.....if i understand correctly, this is the sense wirre . making this setup a one wire in reality?
if this is correct all i need is that wire and the other battery positive red wire......that should give full alternator output to the batteries ?
then all i need to do is sort out the tach and the idiot lamp ....correct?the lamp is pretty clearly marked with the L......and according to a code i read somewhere the p terminal is the tach.......I have been reading for three days now and forget where and what i read .....but i did write down that code...plus i can do the lamp and tach at a later date? as i am not even sure they work at all......thanks everyone...Ron
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Old 01-05-2011
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Lester 7973N comes up as a replacement for a Delco CS130 alternator:

WAI Global Part Details

Call DelcoRemy at 1.800.372.0222 (They actually talk to civilians without complaint!) the unit is obsolete so it isn't on their web site any more.

WAI are actually wholesalers, if you have a business with a tax ID# they are a great source for systems and parts (i.e. diode rack) way below retail prices.

The CS130 was apparently superceded by the CS130D and there is a CS130DSE, SE for self-excited, i.e. your one-wire hookup. Delco alternators (Delcotrons) will maintain a tightly regulated 14.3-14.3 volts when used in the normal sense wire configuration, turning it into a 1-wire is cruel and unkind to your batteries.

I did find a note at How to Wire a GM External Regulated 10DN alternator, Delco Remy External Regulated Alternator Wiring that IF YOU CONNECT THIS ALTERNATOR WITHOUT A RESISTANCE or lamp in the "L" wire, you WILL BURN OUT THE INTERNAL REGULATOR. So don't hook up too hastily. The idiot lamp marked "L" is critical, not optional, and while you are in there this could be a good time to replace that lamp, just in case.

Here's a link with diagrams of some wiring options:
Delco Remy CS130 & CS121 Series Alternator Repair Manual, Page 3

You can use a sense wire with two batteries, if you use a battery switch that has the extra "field" wire switching. Run the sense lead to the second set of contacts, instead of the field wire, so it switches batteries when the main power switches. (And of course, don't switch while the engine is running.)

Last edited by hellosailor; 01-05-2011 at 02:04 PM.
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thank you for all the help I think understand it now, i will repair the lamp circuit as needed .. befor firing it up ....thanks again Ron
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