article written by Jean Des Rosiers
I am rebuilding my café racer and adding an Alton electric starter, since space is at a premium, I opted for a Ballistic lithium battery.
These batteries require a slightly higher voltage than standard or AGM lead-acid batteries.
I read that some got on quite well using the lithium batteries with a “standard” Podtronics or similar combined regulator/rectifier and while the battery was not 100% charged, it was OK to get the bike going.
I ordered a Chinese replacement regulator/rectifier and when I got it, I tried it on a 12 volt AC transformer to see how it would perform.
I wanted to know if it was stable, would heat up…
As soon as I connected it to my transformer and powered it up, my test leads just melted, so I figured it was defective.
I measured it and it was not shorted, yet just touching the input wires to the transformer just produced sparks!
What was going on with that thing?
I borrowed a genuine Podtronics from my friend and did the same test… same thing?
So I started to investigate and this is what I found.
This is the basic circuit for these regulator/rectifiers:
The GREEN rectifiers (this is a 3 phase model) take the AC from the alternator and turn it to pulsating DC, the battery smooths it out.
As the battery voltage rises, the control circuit turns on the RED SCRs to effectively short out the input or to put it another way, short out the alternator.
I have worked all my life in computers and electronics and this does not make sense to me.
My test setup consists of a pair of transformers hooked up to give me 3 different AC voltages, about 13.5 V, 16.5V and 19.5V.
Look at the waveforms at the transformer output with a Podtronics type of regulator/rectifier.
My transformers are 250 VA so more than a good 3 phase alternator.
This first picture is with the first tap (13.5 V)
AC current is 28A, AC volts is 9.6 and DC volts at the battery is 14.34 with no load.
Second tap (16.5 V)
AC current is 25A, AC volts is 8.1 and DC volts at the battery is 14.4 with no load.
Third tap (19.5 V)
AC current is 19A, AC volts is 7.2 and DC volts at the battery is 14.4 with no load.
I added a load consisting a 6 ohm resistor in parallel with a 2 ohm resistor, this in theory would be a 8 amp load, but my wires are somewhat undersized.
Now watch what happens…
First tap (13.5 V)
AC current is 5A, AC volts is 12.8 and DC volts at the battery is 11.8.
Second tap (16.5 V)
AC current is 6.8A, AC volts is 14.1 and DC volts at the battery is 12.1.
Third tap (19.5 V)
AC current is 7.3A, AC volts is 14.6 and DC volts at the battery is 12.2.
As can be seen, as long as the voltage is below threshold, the rectifier acts as a basic bridge.
Now watch what happens when I reduce the load to only a 6 ohm resistor or about 2 amps…
My conclusions with this type of regulator/rectifier are:
- NEVER use them without a battery
- NEVER run them without a load
They work, but they are not kind to alternators and as far as using them with lithium-based batteries, this is asking for disaster, the voltage of lithium-based batteries being higher, they will short the alternator more than with a lead-acid battery, a shorted alternator will heat up and some day burn up.
The less load there is, the bigger the hit on the alternator.
Now the old Zener diode that many shun for obscure reasons… there are some reasons to use something else, the main one is the Zener is made for positive ground systems and the other is that a separate rectifier is required.
This is the alternator waveshape at 13.5 volts with only a rectifier and a capacitor, connected straight to the battery.
I did not test it at higher voltages because the DC voltage of the battery would have gone too high.
On the first tap of the transformer (13.5V) my readings were:
AC current 0.6A AC volts 13.5 and DC volts at the battery 16.0 with no load.
Now I connected the Zener and here are the readings.
First tap 13.5 volts from the transformer:
AC current 1.7A AC volts 13.2 and DC volts at the battery 15.0 with no load.
Second tap 16.5 volts from the transformer:
AC current 4.2A AC volts 15 and DC volts at the battery 15.9 with no load.
Third tap 19.5 volts from the transformer:
AC current 5.2A AC volts 16.2 and DC volts at the battery 16.4 with no load.
The old Zener is kinder to the alternator since it only clips the TOP of the AC waveshape, it’s regulation however is very approximate erring on the high side.
There are ways to use it on negative ground systems by using stud mount rectifier mounting hardware which electrically insulates the stud from the heat sink, but most people won’t bother and will use a Podtronics or similar not knowing what I have shown previously.
Out of the two so far, I would rather use a Zener than a Podtronics or other similar product.
On each test, the Zener is “wasting” more and more energy, even without a load, going from 23 watts to 63 watts to 85 watts.
Obviously with a load, some of that wasted energy would go to the load and the rest out in heat.
Another interesting bit of information:
With a battery sitting at 13 volts, here is the current draw with the regulator connected
- Zener 0
- Podtronics type 0.416 mA
This means the Podtronics type will drain the battery over time.
The Zener has zero draw since that is below its design voltage.
I ordered a Shindengen SH775 from eBay – this is a series-type regulator/rectifier also known by some as open-type (because it better describes the way it behaves with the AC supply from the Alternator stator).
It IS more expensive than the short-type, but it performs way above the others.
So as before, first tap of my transformer:
AC Amps 1.2 A AC volts 13.5 DC volts at the battery with no load 14.4
This waveshape is on the AC side, the red line is current and the green line is voltage.
As can be seen, the regulator turns ON to pulse the battery with a current spike.
And this wave shape is what the battery sees with a 2 ohm load (6 amps)
The average voltage is a bit below 13 volts.
Going to the second tap:
AC Amps 1.7 A AC volts 16.1 DC volts at the battery with no load 14.5.
With a higher voltage, the regulator does not need to turn on as often.
This is what the battery sees with a 2 ohm load.
And finally, the third tap.
AC Amps 2.0 A AC volts 19.0 DC volts at the battery with no load 14.58.
Again, with higher voltage, the regulator turns on even less.
And again showing what the battery sees with the same 2 ohm load.
This regulator/rectifier is very “kind” to the alternator, it does NOT short out the stator windings so this means less stress on the alternator, the wires and all the connectors leading to the alternator.
It is more expensive, but if it saves an alternator, it is worth every penny.
My analogy of the Podtronics short-type regulator/rectifier is a vehicle without a throttle whose speed is controlled only by applying the brakes.
The short-type of regulator/rectifier is not new, it is very widely used on many bikes, but any imbalance such as adding or removing loads, changing bulbs to LEDs, running with a blown bulb may result in failure of the alternator, the regulator/rectifier or both.
What is most puzzling is that similar components are used in the construction of both the short-type regulator/rectifier (like the Podtronics) and the much superior series-type (also referred to by some manufacturers as open-type), so cost of components is not an issue.
It is only the fact that short-type regulator/rectifiers have been the normal for so many years, meaning that the production numbers are much higher so the cost is therefore lower.
There are many people who have found the same things that I have and they are replacing the regulator/rectifier in their bikes with a series-type (open-type) one for better reliability, many manufacturers have also switched and gone to a series-type (open-type) mainly because they are offering longer warranty periods.
My Suzuki V-Strom 1000 has a series-type regulator/rectifier as standard equipment, since it is used very often as a touring bike onto which people add things like heated grips, heated vests, lights etc…
Plus, it has a 5 year warranty, the chances of the alternator burning up was not something they really wanted to have and neither did the riders asking for absolute reliability.
Series-Type Part Numbers
The Shindengen numbers are SH775 for the 35A model and SH847 for the 50A one.
The SH775 is used on certain Polaris models like the Ranger and the part number is 4012941.
The 50A model is the SH847AA – OEM Suzuki Part Number 32800-31J00.
Beware of copies sold on eBay, the real ones have a stainless steel plate on the back, the fake ones are potted.
There is a great video from Jack at Roadster Cycle – Jack is a great source to buy these units from over in the USA!
In the video, Jack points out how to spot a fake unit.
My rough rule of thumb is that if the units are less than $100, they are probably fake!
The real ones can be connected to an AC supply 12-20 volts and will not blow any fuse or burn wires, the fake ones WILL.