regulator/rectifier blown fuse

Hello all ... my mity max died last week so I replaced it with a Podtronics unit rated for 200w. I have a Boyer Bransden MK4 ignition and a high out put single phase Wassel alternator and wired up new reg/rec the same as the mity ( positive earth ). My problem is after a mile or so of normal performance the fuse in Neg. wire burns ( 15 watt blade type ). Luckily so far I have not been stranded but sooner than later I will run out of spares. Tonight I put in different plugs BPR7ES previous plugs were BP7ES to see if that helps, it idled fine but didn't road test, that will be tomorrow. Any thoughts or suggestions would be welcome
Craig

The rated fuse according to the manual is 35amp but that is in British ratings.
The US rating is half that. So 17.5 amps would be US ratnig. I Put in a 15 spade type and it blew.
I put in a 20amp and all is fine.
I think the electronic ign, lights and gauges draw more than normal but I can't be sure.

Sorry I left out what power I'm using ... halogen head light , horn and brake light that's it ... no markers,no idiot lights just the minimum ... I'm wary of going to a 20w fuse without knowing why , when 15w worked for 9 years with same setup
Craig

Craig said:

...I'm wary of going to a 20w fuse without knowing why , when 15w worked for 9 years with same setup
Craig

Click to expand...

I've had to use a 20-amp (US) fuse forever in my '74, and that was with the stock system.
Now, if your battery was failing, it could be sinking too much current, thus blowing the fuse, especially with the increased capacity of the 200w system. If you're not blowing any bulbs, then the voltage isn't too high, pointing again to the battery.

Nathan

I increased capacity 9 years ago with 180w alternator that's when I put mity max on ... battery is new and good ... if it's considered reasonable and there is no possible damage I will try 20a fuse ... just wish to know why I should need it now given the facts above
Craig

I have hi-jacked this from a different website, but it explains why the specified US fuse rating difers from a UK specified fuse................

"British and American standards for rating electrical fuses are different. Both provide an “Amp Rating” for very similar looking fuses, but the two ratings mean very different things. The US system rates the fuse based on the continuous load it can handle for a specified period of time w/o blowing, whilst the British system expresses the load at which the fuse will immediately blow.

That’s a significant difference! As an example, the 35 Amp fuse called out for many 1960’s/ 70’s bikes is roughly equivalent to a US-spec BUSS AGC 17 Amp fuse. Install a US 35 Amp fuse into your fuse box and the wiring harness will melt down before the fuse blows.
The complete rating for the specified 35 amp Lucas fuse is…

“17 AMPS CONTINUOUS / 35 AMP SURGE”

Early British fuses were simply marked with the quick-blow rating, but later fuses are given two ratings in an effort to minimize the confusion. For instance, the 35 Amp fuse is often marked as “17 continuous/ 35 blow”, or simply 17/35. In that case, use the lower “continuous” rating as the one to which you try to match an American BUSS fuse rating".

Do you think I would fry my ignition or other component by going to 20a fuse based on this info ?
Craig

Craig said:

Do you think I would fry my ignition or other component by going to 20a fuse based on this info ?

Click to expand...

It's excess Volts that destroys electronic ignitions, not Amps. Excess Amps destroys wiring. A 15Amp (continuous rated) fuse should blow at around 30 Amps, and the typical average current (Amps) drawn by your bike's electrical system shouldn't be more than about 10 Amps maximum, although it may increase temporarily if the horn is used, so you need to find out what's causing the additional 20+Amp load (equal to running another 4 or 5 extra headlamps) or intermittent or partial short circuit that's causing the '15A' fuse to blow.

Thank you guys, I will start the search ... although no changes to wires for some time ... any suggestions for usual places that fail or easy way to check ... strikes me as odd that once I replaced MM I started burning the fuse ... and Lab is probably correct in suggesting intermittent short , which are really difficult to locate ... after a quick look nothing is obvious ... oh well
Craig

A 200 watt alternator divided by 14.7 volts ( typical charging voltage) is 13.6 amps ( maximum amps)

The usual engineering practice is to multiply max amps by a factor of 1.25 to obtain the fuse rating. 13.6 x 1.25 = 17

From this calculation, a 15 amp fuse is inadequate....the next rating is 20 amp....go with that

Slick

Start the slow laborious search for chafed wirings.

Just back from shed after tracing wires , not that many as very basic layout ... all I can find is good wire and good connections ... only oddity was intermittent front brake light switch ( brembo master cylinder micro switch that I fiddled with and got working )... For clarity I should mention the battery has tender on at all times when not in use ... I suspect the Mity Max has been dead for some time ... longest run this year was 45 minutes each way with lunch in between blast over mountain ... I could have made it without charge being delivered to battery I think ... So what kind of damage do I risk by going to 20A fuse ? Thanks to all respondents !!!
Craig

Craig said:

..... So what kind of damage do I risk by going to 20A fuse ? Thanks to all respondents !!!
Craig

Click to expand...

In my previous post, I gave you the usual engineering methodology to determine fuse rating (17A). It is also usual engineering practice to use the next higher standard rated fuse (20A). I would not lose any sleep over it.

as to your obvious question....Why did a 15A work with my previous regulator? I cannot answer that with any specificity, only conjecture....perhaps the new Podtronics has advanced circuitry that responds to load changes faster than your old unit....that would cause amp spikes that might not have been present with the old unit.

Slick

Thanks Slick , I will try 20A and go for a ride and report in later ... Happy Canada Day !
Craig

Yes, Happy Canada Day ! Driving Crazy Combat over to Woodbine for Tribute Bands then Beaches Fireworks. Had a charging issue myself 2 days back until put new connectors to Alt. output joins under airfilter. Sloppy. Electrical gremlins so fun.

I've been using the 20A USA fuse for since when I can remember. I've only got the 130W alternator.

Dave
69S

Had bike out for test tonight with 20A fuse installed ... got about 1 mile and a bit and puff blown fuse ... replaced with another 20A and turned around made it about 400 yards and puff blown again ... replaced with 15A as that was what was left and continued on home ... sat in lane to shed with bike still running and pulled and pushed on all wires I could get at ... had headlight on both brakes and horn and ran like a champ ... ran it at idle a couple of minutes and then at 2500rpm and all good ... shut it off put it in shed and checked all wires and connections all good only fly was a loose and frayed wire in left hand switch cluster which is my headlight ... I re-soldered it and made sure horn button was clean and releasing properly ... I'll have to wait now till Thursday to try it again ... anyone have any other suggestions ... thanks in advance
Craig

When you replaced the reg/ rectifier unit with the Podtronics, are you sure you got the ground (earth) polarity right?

On the Podtronics unit, the red wire is positive, the black wire is negative. If you are running negative ground, the black wire should be grounded; red wire grounded with positive ground.

Does the Podtronics get warm without the engine running? If so...that would indicate reversed polarity. A charged battery and a patent fuse must be in the circuit for this test.

According to your first post, the only thing you did was install the Podtronics....then the fuses started blowing. That would seem to point to the Podtronics installation.

Slick

I hear you and the install is good ,,, positive ground same as before ... the unit does not get warm ... guess I'll keep digging
Craig

I use the "divide and conquer" technique to find shorts. Try to isolate (divide) a portion of the circuit from the rest, i.e. take it out of the circuit, then see if fuse blows. If not, then fault is in part so isolated... if fuse still blows, divide again.
It helps to have a wiring diagram for this, or simply disconnect bullet terminals to take a part out of the circuit.

Another technique is to remove the battery, and install a VOM (on ohm scale) across the main terminals. Then do the tugging, wiggling, while watching the meter....if you get a flicker, you are getting close. Connect positive meter terminal to ground with pos ground system.

Good luck!

Slick