Wiring a solid state rectifier

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We all use the wrong word, quite frequently!

I would dispute that the Zener can aptly be described as a load on the alternator. Isn’t the reverse impedance of the Zener pretty low, so it’s more like a short than a load? I must admit I’m having difficulty finding facts and figures for Zener impedance, on popular search engines.
 
Triton Thrasher said:
I would dispute that the Zener can aptly be described as a load on the alternator. Isn’t the reverse impedance of the Zener pretty low, so it’s more like a short than a load? I must admit I’m having difficulty finding facts and figures for Zener impedance, on popular search engines.
Click to expand...

At voltages below the zener's breakdown voltage the diode is reverse biased and draws no current. The zener becomes a load, (draws current), when the peaks of the rectified AC waveform exceed the zener voltage. At that point they do become very low impedance and the current is limited by the source impedance of the stator. Designers don't normally consider the "impedance" of the zener itself, only it's power/current rating.

Example, if you have a 15 volt zener and a 20 volt source with 2 ohms of source impedance, the zener current would be (20-15)/2 = 2.5 amps and the zener's power dissipation would be 2.5 x 15 = 37.5 watts. But only during the period of the waveform where the applied voltage is above 15 volts.
 
maylar said:
Example, if you have a 15 volt zener and a 20 volt source with 2 ohms of source impedance, the zener current would be (20-15)/2 = 2.5 amps and the zener's power dissipation would be 2.5 x 15 = 37.5 watts. But only during the period of the waveform where the applied voltage is above 15 volts.
Click to expand...

Ok 2.5 A is going through the Zener. Is the voltage drop across the Zener really as high as 15 V?
 
Triton Thrasher said:
Ok 2.5 A is going through the Zener. Is the voltage drop across the Zener really as high as 15 V?
Click to expand...

Yes. Depending on the application. The zener test in the service manual says 13.5 to 15.5 volts at 2 amps. If I were to pick a zener for a single phase 120 watt system I'd pick 14 volts (+/- 5%). For the MKIII circuit that LAB posted above there's an extra diode voltage drop after the zeners, so I'd pick 15 volt zeners for that.
 
Wiring a solid state rectifier

2 amps @14.8V for a single zener in parallel to the regular charging circuit, this is a regular Lucas zener rated 14.3V
 
maylar said:
Yes. Depending on the application. The zener test in the service manual says 13.5 to 15.5 volts at 2 amps. If I were to pick a zener for a single phase 120 watt system I'd pick 14 volts (+/- 5%). For the MKIII circuit that LAB posted above there's an extra diode voltage drop after the zeners, so I'd pick 15 volt zeners for that.
Click to expand...

So the impedance of the Zener, in breakdown, is several ohm?
 
Triton Thrasher said:
We all use the wrong word, quite frequently!

I would dispute that the Zener can aptly be described as a load on the alternator. Isn’t the reverse impedance of the Zener pretty low, so it’s more like a short than a load? I must admit I’m having difficulty finding facts and figures for Zener impedance, on popular search engines.
Click to expand...
You are correct. As I was dealing with a member who isn't an electrical engineer, I was trying to describe it in a way that I hoped [don't know how well I succeeded] he could easily understand. I used an analogy that most people are familiar with.

Charlie
 
Triton Thrasher said:
Ok 2.5 A is going through the Zener. Is the voltage drop across the Zener really as high as 15 V?
Click to expand...
The voltage "drop" is not 15 volts. You are trying to limit system voltage to about 15 volts. Above 15 volts, a battery, if it's not completely discharged, will heat up. The electrolyte will boil. If the 15+ volt charging event lasts long enough, the battery will overheat to the point that the lead plates will warp and short out. When you see a battery where the side walls bulge outwards, you know that at some point, that battery was a victim of such an event. At or above 16 volts, your light bulbs will start to blow out [if the lights are on].

Grant, I want to thank you for making me aware of the advanced aftermarket products now available for the red, charging "idiot" light for our bikes. Good stuff. Don't stop posting to the forum. You are not preaching in the wilderness.

https://www.improvingclassicmotorcycles.com/products.htm

http://roadstercycle.com/Motorcycle voltage monitor.htm

https://gammatronixltd.com/epages/b...6-4572-89a1-e89006e78fbe/Categories/Category1

Charlie K
 
@chaztuna no intention of stopping posting just yet.

I just step out of a thread when I have said my piece and the vultures descend with their knit picking, condescending comments and negativity.

I pay more for a VIP membership here than I do to run my own website, as I feel it is a great resource and on the whole a great community.
In places like this, there will always be personality clashes but the bottom line is that we are all in the same boat together, we all have the same love for Norton Commandos but I for one don’t log in here for the snidey comments and bullshit.
It ruins it for me and I assume for everyone else.

...anyway we digress - this thread has gone wildly off track, and poor old Ellis is probably running for the hills.
He only wanted to wire up his new rectifier.
 
gtiller

I would like to thank everyone for their posts even if i don't fully understand it all. This is a great Forum and if people only take in 5% of the information posted then its doing what its intended to do. I still have a few things yet to checkout so will keep you all informed on my progress. If i need to replace one or both Zenners does anybody know of a supplier in the UK, and do you know the part No as my usual suppliers AN and RGM both say they are out of stock.

Cheers ELLIS
 
@ELLIS the Lucas part number is LU49345A

The best you can hope for is that someone will have a spare in their garage having fitted an aftermarket reg/rec to their bike.
They do show up on eBay from time to time.

Wiring a solid state rectifier

Lucas/Wassell did start making them again, and a few places began stocking them, but reliability was not good and failure rate was high.
So that would not be my recommendation.


Some of the guys on here were talking about an aftermarket option from a reputable manufacturer, so it is worth keeping an eye on that thread.
The required unit 1N3313RB is not usually stocked (we are now living in a negative earth world), so it would be a special order.
 
Triton Thrasher said:
In that case, the power dissipated as heat would surely not be Mr maylar’s 37.5 W, in that example?
Click to expand...

Apologies if my numbers are misleading, as they represent peak values not continuous. My graphics drawing is limited to MS Paint, so the below is rather crude, but it demonstrates what the zener is actually doing on a full wave rectified single phase system:

Wiring a solid state rectifier
 
gtiller said:
Some of the guys on here were talking about an aftermarket option from a reputable manufacturer, so it is worth keeping an eye on that thread.
The required unit 1N3313RB is not usually stocked (we are now living in a negative earth world), so it would be a special order.
Click to expand...

The standard connections on stud mounted diodes is that the anode is connected to the case (stud). The anode of a zener needs to be negative, so the standard configuration works as-is for negative earth. They could be made to work on positive earth if the diode was electrically isolated from ground. A mica washer with heatsink compound, an insulating sleeve around the stud, and a phenolic washer on the nut side would insulate the diode electrically but not thermally from the z-plate.
 
maylar said:
Apologies if my numbers are misleading, as they represent peak values not continuous. My graphics drawing is limited to MS Paint, so the below is rather crude, but it demonstrates what the zener is actually doing on a full wave rectified single phase system:

View attachment 18924
Click to expand...
Nit picking ? Or is it telling the truth? The graphs do "generally" show what is going on.
AC volts is for open circuit (nothing connected to alternator) and assume 20v is OK
Zener volts clipping starts @ 14.3v per my graph and would actually have a slight bowing on top, not flat as the current was being shunted to ground.
Zener current pretty much correct. zero current at 14.3V and 2.5A @15.1V
voltage and current are both sinusoidal in nature and pulsed . This is not DC so voltages and current are not continuous.
 
@maylar my apologies - did I quote the wrong part number or something?

I thought 1N3313RB was correct for positive earth machines?
The 'R' being "Reverse" polarity where the cathode is attached to the z-plate.

I personally don't feel it is a good option to even consider switching a zener round the other way - heat conductivity is really important, especially for a bike with LEDs on it.
 
gtiller said:
I thought 1N3313RB was correct for positive earth machines?
The 'R' being "Reverse" polarity where the cathode is attached to the z-plate.
Click to expand...
You are correct on both counts. Unfortunately nobody stocks the reverse polarity and people have reported some bogus replacement zeners in the current market. Diode mounting hardware is standard electronics stuff, Google "D0-5 Diode Mounting Kit". A bit of Dow Corning 340 on the insulator and Bob's your uncle.

Or... convert to negative earth.
 
All I seem to be doing is annoying people, but what I’m interested in is the impedance of a Zener in a typical Britbike installation, when it is conducting at or over its Zener voltage or breakdown voltage.
 
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