TOPIC: Voltage Regulator for Merc 500 Thuderbolt

Has anyone retrofitted a voltage regulator to a 1967 Merc 500 Thunderbolt, or similar? I find it pretty disconcerting to cruise around with the voltage regulator reading 17-18 Volts. I'm using a Marine Starting battery (not a deep cycle) and so far no problems, but I'm new to this and I've only got a few hours experience with it. How did they get away with the 'no regulator' design back then? Obviously it worked well enough that didn't think it was a necessary part to put on the motor, but what was the downside? Maybe they just replaced the cooked battery every year?

Thanks for any advice on this,
Bill

they got away with it because it only puts out about 3 amps.

if you are worried about it put on the running lights or radio etc.

Actually that is what I did - turned on the lights. I thought maybe someone had worked through this and knew of a regulator retrofit that would work. I'll measure current output and research it a bit, but no sense in going too far into the issue as it obviously has not been a big problem.

There's a thread from a couple years ago on here somewhere (probably in the archives?) from when Frank put one on his Merc1000 with the help of Dr. Frankenmerc and the other Merc guru's, Bill. As I remember it contained the part number for the regulator style rectifier, how to hook it up, etc.. We'll have to see if we can find it for you.

I know it's a little concerning to see the voltmeter pegged like that, but as long as you stay away from maintenance free, agm, and the fancy batteries a good one will still last 3 to 5 years for you. Just make sure you keep the water level up.

Many lawn tractors charge at 3A and spike as high as 20v, any lead acid battery can take it if you keep it full.. If you want a regulator for your accessories, Radioshack has 12v regulators you can use in line with the electrical feed to each accessory

Here is the regulator I recommend you use & the wiring instructions required.
Don't forget to eliminate your original rectifier as this regulator has one in it.
They are pretty spendy,...But used ones can be found on EBAY for between $40-$70ish.
The replacement CDI/Rapair components that they make for Mercs warns that uses of an unregulated charging system will cause voltage spikes and subsequent failure in the ignition components.
Doc F

Thanks Doc, that is exactly the info I was looking for.

Have to admit that I was getting kind of down on the old Merc until overhauled the carbs. Now this thing just purrs, setting the carbs rich at idle was just the ticket to get rid of stalling and it is really strong at wide open throttle. So, going the extra mile to get this regulator setup correctly seems worth it now that everything else is going right. Sure would hate to wipe out an ignition module.

As Tom Bodett says "I'll keep the lights on" at least until I find a regulator.

Thanks again,
Bill

Here are a couple of reasonably priced used regulators on eBay.
Caution though - not all regulators that 'look' like these will work.





Doc

OK, so does anyone know how these regulators work:



I also saw a single-wire Quicksilver version on eBay:



I know the Doc has installed similar regulators, used in the past on V6 Mercs, on Inline motors. I wonder if the 2-wire reg works the same as that one.

The single-wire one is interesting, too. I'm thinking that maybe all of these work off the "zener diode" concept where the voltage is clamped to a certain level.

Thing is, the "Tympanium" regulators are Dirt Cheap online and are used in various configurations, on tons of dirt bikes and other equipment.

Here's a 2-wire regulator for less than $14:

www.motorcycle-superstore.com/2/9/195/7315/ITEM/MSR-Voltage-Regulator.aspx

If we can figure out if these will work in an outboard application, it'd be a really cheap and easy way to retro-fit a V.Reg.

Cheers.......ed

That's the problem, you need to know how these things work, and whether they can be made to work with the exact application we are trying to regulate. Most charging systems that I am familiar with have a field circuit that is controlled by the voltage regulator. My Merc 500 has no field circuit. It works by having a permanent magnet rotate past coils of wire. It appears to me the only thing you can do in such a case is to shunt the unwanted current through a resistance, i.e., 'sink it'. That creates a lot of heat so you need to have a regulator with some metal, and airflow over it, to get rid of the excess heat. Actually, there are more sophisticated ways using SCR regulators, but they are even more expensive.

That is why I asked if someone had already worked through this issue. Figuring as old as these engine are someone has already done it and has actual experience with the solution. Doc replied with a solution, albeit somewhat expensive, but, at least we know that it will work. Some of the other regulators would require some testing before we could say whether they will or will not work. If they are meant for systems that have a field circuit then they surely will not work for us here.

Bill

These are not "field" type regulators, they are zener-diode type which shunt power to ground to keep the voltage down to a reasonable level. The thing to find out is if they have enough "ampacity" to work in our marine application. Considering that they are an outboard part to begin with, I figured that some Force or Chrysler outboard used it.

I did find out that some of these are used to keep motorcycle lights at a regulated 12V, which wouldn't of course work for a charging circuit, since you certainly need more voltage than that to keep the battery charged.

Doc has already proven that the zener-type of regulator that Merc used on certain older V6 models works great. Just trying to figure out if these "F745470" units would work. The seller on eBay has a whole bunch of 'em and states that he would give a quantity discount.

It'd be great if someone had a modern "where used" Merc/Force parts book, so we'd have somewhere to start at. If I knew what the application was for this part, I'm sure I could figure out if it'll work.

Or maybe I'll just order one and the Doc and I will have to have a little experiment. Just don't worry if you see a bunch of smoke signals coming from Doc's Place!!!

(regulator pic courtesy of Doc FrankenMerc)

Cheers................ed