Source for charging system diodes?

[Bill Allert 68]

I just checked the 2 charging system diodes on my Lawn Ranger L-157, and they are bad. These are the ones that plug in like a bus fuse. Does anybody know if replacements are available, or do I have to go to an electrical supply house & get one rated for >6amps & solder them in ?? Thanks! Bill

[Jake Kuhn 1,555]

Bill,

send a pm to wheelhorse656 on here. I got a set from him before and he sold many tecumseh parts. Not sure if he still does but it is  worth the try to ask him about them.

 

Jake

[Bill Allert 68]

I found what I'm looking for; look at the attachment and you will see the diodes soldered in. Under $1.00 vs $29.00 for the NOS rectifier I found on Ebay!!!

[KATO 115]

I saw that one on E-BAY also 29.00         

[Lane Ranger 10,974]

^{The  posting Bill made above is the avenue I took with my Lawn Ranger Tecumseh motors.   I rebuilt three rectifier boards with the 3 amp diodes from Radio Shack and the other parts that Ed Stoller mentioned.   They work and do the same thing the original diodes did and they will produce the same electrical output!}

 

^{Ed Stoller did three articles in the Lawn and Garden Tractor Magazine a couple years ago that highlighted this issue.   The bigger HH 100 Tecumseh 10 HP electronic coils are also an issue that many Tecumseh motor owners have dealt with.  Ed Stoller came up with a solution for that one too!}

[305 380]

i actually "fixed" the diodes on my lawn ranger instead of soldering in new diodes. if you pry the old diodes apart you will see that it's just a shell with a diode inside it. i replaced the insides with diodes from radio shack part # 275-1143 . then just snapped them back in

[wheeledhorseman 574]

You beat me to it - I have one duff diode and was wondering if this could be done but hadn't got round to it so now I know.

 

I only became interested in these as a result of picking up an A-800 Ranger earlier in the year. The charging system is described by Tecumseh as a 3 amp but they qualified this by saying the combined output of the two diodes. They were essentially 'bigging it up'.

The original diodes in mine were 1N1084, a common diode in the 1960s, not specific to Tecumseh, but long obsolete now. Looking up original data on these they were in fact only rated 0.5 amps and 400 volts but could withstand higher current on a non-continuous basis. 

 

The only reason for trying to replace diodes 'like for like' has been to preserve authenticity though 305 has discovered you can hide a replacement didode inside. Having seen the litlle stator coils under the flywheel I think they'd be hard pressed to deliver 1.5 amps but its on my list to check out when the tractors together and running again. The charging system was only needed to replace energy taken from the battery by the starter motor. It has no regulation but according to Tecumseh data doesn't begin to charge at all until about 2500 rpm is reached, full charge at 14 volts requires at least 3000 rpm or more.

 

The low output from the alternator together with the fact that these old 1N1084 diodes dropped up to 1.5 volts (compared with about 0.6 volts by a modern diode) meant it was hard to end up with an over charged battery. However, Tecumseh recognised that it could happen and suggested if the battery is noticeably bubbling then remove one of the diodes to halve the charge.

 

Replacing the originals with a modern diode should actually improve the charge rate but increases the chances of overcharging if the tractor is operarated at full revs for long periods. All of which I intend to investigate once my little ranger is back together and running again.

 

Interesting thread.

 

Andy

[305 380]

the diodes i used say 3 amp  ,  but i figured with two of them i'd give it a try.   i just checked them and they are still good after using them all last year to mow my lawn

[305 380]

i have to add that it was kinda of a pain to do since you are working with real small parts

[Save Old Iron 1,566]

Justin, the original 1N1084 were rated for 400 volts but only 1/2 amp - yes, 0.5amp.

 

I'm not sure about why the designers used a 400 rating but the diodes in HH would not see a reverse voltage higher then the battery voltage plus the peak value of the negative sine wave coming from the stator windings. In other words, when the diode is blocking half the AC wave from the stator, it blocks that peak voltage PLUS the voltage from the battery.

 

Let's guesstimate the peak voltage from the stator is 17 RMS AC which translates into about 50 volts peak which the diode must block from the stator alone. Add to that peak value the DC value of the battery (15 ish). The total voltage the diode must block is 50 + 15 or 65 volts total.

 

If you calculate a safety margin by doubling the 65 volt requirement, a 200 PIV or (P)eak (I)nverse (V)oltage diode should be fine. Correction. I guess I'm showing my age saying PIV, modern term appears to be Vdc or maximum DC blocking voltage.

 

A 3 amp rating should be more than sufficient.

 

So we need a 200 PIV 3 amp diode.  That would be the 1N5402

 

To answer your question on if additional diodes can be mounted to the HH board. Yes, you could solder a few diodes in series and place them into the holders on the existing pc board. The arrangement may be a little messy, but electrically it is no problem. I might start with 3 diodes in series in each leg of the HH board. The 2 additional diodes would knock off about 1.3 volts of charge voltage. You could easily monitor the battery voltage after a long session with the tractor. Target about 14.5 volts on the battery while the engine is running at full speed. If you run the engine at lower than full speed, 2 diodes may be more appropriate. If you do a bit of work with the tractor in colder weather, one diode in each leg would be good. Remember, colder weather requires a higher charge voltage to maintain good battery health and promote longer battery life. Higher charge voltage which could overcharge a battery in the summer is just about right in the winter.

[tombones49 3]

I have a Tecumseh V7 engine. The rectifier assemby is exactly what you have shown in your diagram. Thanks ever so much for posting the fix. Just for fun, I altered your image for clarity and added a bit of information. Aside from that, can I check the existing rectifiers with a multimeter? How?

 

tombones49

[Bill Allert 68]

Yes, checking them is easy; using your ohm meter, you should have continuity one way but none when the leads are reversed. No reading either way means they are bad. The direction of flow is towards the band.

I took up repairing tube radios while I was laid up with a broken hip last year, & learned that when rectifiers ( they convert ac voltage to dc) went bad the fix for those old radios was to put in a $1.95 diode in its place!!! 

[Save Old Iron 1,566]

this may be of interest if you need additional help with diode testing

 

http://saveoldiron.47.forumer.com/testing-diodes-t2224316.html

[WHX?? 48,853]

Digging this one of the cellar & @305 might be my hero today.  Diodes toast but they indeed do come apart for replace the diode inside. Found two on

flea bay for chump change so pulled the trigger. PN is 276-1143 or 1N5402 as SOI mentioned above. 

Found them HERE as well.....  talk about highway robbery!

 

[WHX?? 48,853]

Since SOI's old reference is gone another good tutorial on diodes. 

https://www.fluke.com/en-us/learn/blog/electrical/what-is-a-diode

[WHX?? 48,853]

The replacement diodes fit perfect in the bodies. The leads are thicker thatn the originals so I just bent them over at a sharp ninety and filed flater with an ignition file for good contact with the ends.

[WHX?? 48,853]

Did a  couple for @Pullstart

 

Forward bias reading. 

[Pullstart 62,950]

Do you just wedge them in, or soldier them @WHX???

[WHX?? 48,853]

Just clip them in. Because of the groove they should only be able to go in one way or with the groove nearest the fuse. Run a wire from the post by the fuse direct to B+ and check charging with a DMM. 

 

There is no regulator on these so they will most likely over charge with extended running. Manual says to remove one diode if it happens. 

Edited April 23 by WHX??