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

carlb wrote:
That's 6A MAX at 50V MAX.

10A will kill it. The internal Diodes are rated for only 6A each. You need a bridge rectifier rated for a minimum of 10A.

Here's a nice one that will handle everything you can throw at it, has nice terminals for blade connectors and a central hole for bolting it to the bottom of your dash or where ever.

http://www.ebay.com/itm/2-20A-1000V-Metal-Case-Bridge-Rectifier-SEP-KBPC2010-/120768921130?pt=LH_DefaultDomain_0&hash=item1c1e637e2a

JimmyM wrote:
Thats 6 amps at 50 volts or to use a common  unit of measure 300 watts.
A load of 10 amps at 12Volts is only 120watts.

The 6amp 50 volt will easily handle the 10 amps at 12vdc.

and yes as i said larger ones are available for penny's more.

Thanks for the link to the Bridge Rectifiers.  My problems is, that I would have no idea what to do with them. How to hook them up, what wire to run where.
I have very little knowledge of components like that. I know that they will take AC voltage and convert it to DC. But I don't know whether they will also provide
a stable and consistent 12V and Current. Or whether I would need another component to do that.  I have no idea.

The power coming from your charge coil will be ac and it doesn't matter which wire you hook up to where on the AC side.  On the output side which is DC it will be marked + and -.   Your voltage will vary with rpm as the output will increase as the engine speed increases but that is not a concern.  I don't think any small air cooled engine uses a voltage regulator.  Even automotive alternators will normally charge to 14.5VDC. Any DC device you hook up on your snow blower be it a light or hand warmers will not care if the voltage varies some. 

Carl

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.