Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

carlb - Thanks for your post. I borrowed the rectifier off my friends Honda tractor.  It's I believe the one Honda calls for to use on my engine.  I hooked it up and took some measurement with a voltmeter.
At idle I was getting an output of around 8.6V. At full throttle it jumps up to right at 30V.
So I guess I'm going to need some type of regulator?  I believe that 13.8V is about all you want to feed a battery? 
The new rectifier has 5 terminals.  2 for the 2 wires coming from the Coil.
1 goes to ground.  And from looking at a wiring diagram for the tractor and the tractor itself.  It looks like one goes to a fuse block (blk w/yelllow stripe) that powers a few relays.  And the last wire (white) goes to the key switch "bat" terminal. But has a splice along the way that goes to the battery + side.  It is fused between the splice and the battery.  Was getting the same V reading from both terminals white wire and blk w/yellow.

HA HA....... Put the Rectifier in the handle bar and make a heater for the grip.....

Looks nice,  did you make the Speed selector plate yourself ?

Friiy

you may find that without a battery attached the voltage is too high.  I would hook a bat up to it and see it it drops back to an acceptable level.  This altenators don't have a lot of output and I suspect that as soon as you put a load on it it will drop right back.  If you don't want to use a battery hook up a 12volt headlight or similar then check voltage again.

carlb wrote:
By that rationale, I could put 10V and 25A though it. Right? or 1A at 250V. In either of those scenarios, the rectifier WILL fail.
The 300W would only be relevant to power dissipation. You can still only put 6A through each diode. And 50V is the PIV rating. Any more than 50V PIV and the diode fails.

You cannot exceed EITHER rating.

Spend the extra $$$ and get a diode that exceeds both your requirements. A much greater PIV is more important to hedge against voltage spikes.

Thanks for the comments. 
carlb - When I hooked up a battery to the system today.  The voltage did come down to right around 12.5V at a high RPM. Remove the battery and I show about 40V at the same RPM.

Question, should the rectifier be getting warm almost a little hot? 

Also JimmyM  the link to the rectifier on ebay that you posted. I've seen one like that before.  Two terminals used for AC input from coil. One terminal to battery+ or + terminal on starter solenoid.
One terminal to ground, Yes?  Will I need a voltage regulator with that rectifier? I don't want to boil the battery.  Should I use a heat sink behind the rectifier?
Sorry to ask so many questions. I'd like to get it right and also learn something in the process.

jrtrebor wrote:
You shouldn't need a heatsink. If you use a screw or bolt to secure it. It should be fine. It will only need a heatsink if you are using it at or near its capacity.

The AC (~) terminals are pretty easy to connect. Typically you'll connect one to the charging coil output and the other to the engine block. If your coil has 2 outputs, connect one wire to each AC terminal. The open circuit voltage is going top be pretty high.
But it only really matters what the voltage is under load. Hook up a 12V automotive bulb to the (+) and (-) connections of the rectifier and see what happens. The bulb may burnout. If you connect your battery to the rectifier output + to +,  - to - the bulb won't blow, but the battery voltage should NEVER go over 14.5V. But let's keep in mind that these charging coils are used for this exact purpose. Also, if your charging coil has only one wire, do NOT connect the (-) output of the rectifier to the frame as a "ground".

A voltage regulator is a bit tougher to talk about. If you add a voltage regulator to this, it won't be like a typical voltage regulator in a car. The one in a car controls the alternator to keep output at about 13.5V. The one you would have to install would not be controlling the charging coil, but simply reducing its output voltage like a self adjusting resistor. It would have to dissipate heat. So at, for example, 17V from the rectifier, and 13V output, you need to drop 4V. At 6A, that means you have to dissipate 24W of power as heat. You can solder with 20W. So that regulator will get plenty hot.

Try the battery and bulb approach first.

JimmyM wrote:
Thanks for your response.  I do have two wires coming from the coil.  I understand what you're saying about the car regulator actually controlling the output of the alt.  Where as the coil on my engine simply
puts out what ever it puts out at any given RPM. My only real concern in this is not sending too much voltage to the battery.  I will be running lights when I need them.  But the rest of the time the battery will
only be used for starting the blower.  The 11hp Honda clone I was using had a 3A coil but it didn't seem to put out enough to keep the battery charged when I was running the light for an hour or two.
I'm sure I won't have that problem with this coil. I'm going to run another check to make sure that when I have the battery hooked into the system.  With the engine running full throttle that the voltage stays
some where between 12.5 and 14.5V.  I guess if I see that, that I'm good to go with buying and installing that rectifier on Ebay.  Any other things that I should know?

jrtrebor wrote:
Hang on. If the coil is designed to be connected directly to a battery, then it's not putting out AC, it's just unfiltered DC. Which is fine for light bulbs and for batteries. What do you think the alternator in your car puts out? Unfiltered DC. In fact, the battery IS the filter for the rest of the car's DC systems. Do you have a volt meter? If so, set it to DC and read the voltage off the coil wires. If you get a positive voltage one way and a negative voltage the other way. Skip the rectifier and just connect the battery and light. You're good to go.

Actually, you'll find a lot of articles that say pulsating DC is better than straight DC for charging lead/acid batteries because it reduces sulfation. OF course, the RMS voltage should still remain in the recommended 12.5 (low float) to 14.5V (absorption phase) range.

jrtrebor wrote:
It does look a little odd, but there could be a couple of reasons.
1. Combining the outputs of a standard "dual output" coil for greater current.
2. Each of the wires going into a single wire may be a diode output so the combined output is fully rectified DC instead of just the upper or lower halves of a half-wave rectified AC wave.

But, for sure, if the wires connected directly to the solenoid (starter solenoid) the you do NOT need a rectifier and the coil is designed to connect directly to a battery since the battery would be connected to the solenoid and ground.

Silly question. Was the meter set to DC or AC?