Mosfet r/r?

[robertbarr]

You can find 775's on ebay from a seller with the name of (something like...) Powersportsnation. Power sports nation. For one thing, they'll show you the ID on the back end of the unit, unlike a lot of sellers. It'll be either SH775AA or SH775BA. I think one has slightly lower voltage output... not that I've ever tested.

Anyway, their units are usually pretty caked with mud, but I've bought several over the ages and they all work fine. Terrific prices, usually. I just paid $26 for one about two weeks ago.

[Steve]

What IS the difference?

The difference is how the MOSFET transistors are used in the circuit. As I mentioned in post #2, MOSFETs are an improvement over silicon transistors. Most transistor designs are rather efficient when they are fully ON or fully OFF. It is during the transition from ON to OFF where they are less efficient and tend to warm up. MOSFET transistors switch from ON to OFF mode quicker, meaning they spend less time in that transition where they build heat, so, yes, they do run cooler. Just like the ad says. But it's only the R/R that runs cooler.

A series-type R/R (like the SH775) could probably use some heavy-duty silicon transistors to do the job. If you really want to get down to it, you could probably use vacuum tubes, but that would tend to offset the efficiency. However, the SH775 does use MOSFET transistors, but only because they are the most efficient way to accomplish the job at a reasonable price.

Because of the difference in operation, the series-type R/R allows the whole system to run cooler. Some feel that the reduction in stator temperature actuall allows the oil to run cooler, because engine oil is sprayed over the stator to keep it cool. Since the stator is cooler, the oil does not have to remove as much heat, so it stays cooler, too.

.

[gsrick]

Come on Rick. Forget MOSFET. Think SERIES. Series type R/R's protects the stator from shunted current heating damage. Simple decision.

I'm not an electrical engineer. I want to know how they work and what the difference is. It's not about making a decision between the two. Most ads don't mention if it is a series or shunt. I know the standard R/R uses diodes(shunt), then they went to diodes and transistors(MOSFET), which I thought was a series. That doesn't tell me why a SH775 works differently than the MOSFET one that I'm asking about. The ad says different from the traditional shunt type, so that leads me to think it is a series. So is it the same as a SH775 if not why?

[Nessism]

I'm not an electrical engineer. I want to know how they work and what the difference is. It's not about making a decision between the two. Most ads don't mention if it is a series or shunt. I know the standard R/R uses diodes(shunt), then they went to diodes and transistors(MOSFET), which I thought was a series. That doesn't tell me why a SH775 works differently than the MOSFET one that I'm asking about. The ad says different from the traditional shunt type, so that leads me to think it is a series. So is it the same as a SH775 if not why?

It's a scam Rick. Those cheap chinese knockoffs are everywhere. They are NOT series type. Do what you want though. Everyone here has told you the truth but you don't want to listen.

[posplayr]

I'm not an electrical engineer. I want to know how they work and what the difference is. It's not about making a decision between the two. Most ads don't mention if it is a series or shunt. I know the standard R/R uses diodes(shunt), then they went to diodes and transistors(MOSFET), which I thought was a series. That doesn't tell me why a SH775 works differently than the MOSFET one that I'm asking about. The ad says different from the traditional shunt type, so that leads me to think it is a series. So is it the same as a SH775 if not why?

https://www.thegsresources.com/_forum/showthread.php?161397-Compu-Fire-SERIES-R-R-Install

SHUNT_vs_SERIES_RR_Compare_Tutorial

[gsrick]

It's a scam Rick. Those cheap chinese knockoffs are everywhere. They are NOT series type. Do what you want though. Everyone here has told you the truth but you don't want to listen.

What is your problem. I'm not choosing anything. I'm trying to understand what the difference is. If you don't know, stop replying.

[Steve]

... I know the standard R/R uses diodes(shunt), then they went to diodes and transistors(MOSFET), which I thought was a series. That doesn't tell me why a SH775 works differently than the MOSFET one that I'm asking about. The ad says different from the traditional shunt type, so that leads me to think it is a series. So is it the same as a SH775 if not why?

Did you get a chance to read my post #17?
That tells why one is better than the other, but not necessarily how they work. Back to basics:

ALL R/R models, regardless of type use diodes. They are the devices that help convert the alternating current (AC) from the stator to direct current (DC) that is needed by the bike. It's actually a pulsed waveform, but it's all on the same side of zero, so it does not change direction. It changes intensity, but not direction. There are three phases in the stator, which allows overlapped waveforms, which evens out the "ripple", so the voltage remains a bit more constant.

ALL R/R models, regardless of type use transistor. What the transistors do will determine whether it is a shunt-type or series-type.
As you have likely heard over and over, when the voltage reaches the setpoint, the OEM shunt-type R/R will SHUNT the excess away from the bike, back through the stator. It now sees the voltage is too low, so it switches the current back to the bike. When it sees that it's too high, it shunts back through the stator and the process repeats. It does this hundreds, maybe thousands of times per second, so the voltage looks rather constant. The problem with this is that the stator is ALWAYS putting out the maximum amount of current that it can. Sometimes it's going to use on the bike, the rest of the time it is being fed back to itself.
A series-type R/R also uses transistors to control the current, but instead of routing it back through the stator, they simply open the circuit to stop current flow. When the voltage drops enough, they close again to allow current flow to the bike. Like the shunt-style R/R, this happens hundreds or thousands of times per second. NO current is re-routed back through the stator. Because the stator actually gets a chance to rest every once in a while, even if it is ever so briefly, it runs cooler.

Both of these R/R styles can use MOSFET transistors. As mentioned in post #17, that will make the R/R run cooler, but it is what those transistors do to the stator current that determines whether the stator can run cooler, too.

Yes, the MOSFET shunt-style R/R can be considered "different from tradtional shunt-type". How? The "traditional" R/R used silicon transistors. The MOSFETs are better than silicon, but that does not make it a series-type R/R.

.

[gsrick]

Yes I did. That reply wasn't towards you, Steve. Thank you for explaining some of what I want to know.

So how does one know which are shunt or series? Is the SH775 the only one or are there others?

I have bought used SH775 R/R before,. but it is a difficult sell to customers. They want something new, so when I saw the R/R ad and it comes with the adapter parts, I wanted to know if it was a viable option.

[Steve]

There are a couple other series-type R/Rs. One that has been discussed many times here is one model of Compufire. I got one of them back before the SH775 was "discovered". I shopped around and got one for a wonderful deal of only about $165 or so. It has been so long ago, I don't really remember. A couple of months later, the SH775 was mentioned and I looked into it. Since I had just spent so much on the Compufire, I was not interested in spending any more money for the new R/R. Back then, the SH775 was available new, from Polaris, for about $80, so it was a considerable saving. Now that everyone has discovered how much better it is, Polaris has raised the price considerably, making the used units from eBay more attractive. If the new ones were still under $100, I would likely spend the extra money for a new one, but I have purchased several used ones on eBay, and have had no problems.

One thing that might help your customers is to present options.
1. A new Suzuki R/R. The actual cost will depend on year and model, of course, but as an example, Parts Outlaw has one for my '80 850 for $243.11.
2. A new Compufire R/R (model 55402) is $213.25.
3. A new Polaris 4012941 (which is a Shindengen SH775) retails for $179.99, but can be had as low as $135 from the link here at Procaliber. Others I checked ranged from $141 to $175.
4. A used SH775 from a Polaris that is available on eBay with prices ranging from $30-50.
5. A new MOSFET R/R from China, purchased on eBay for about $20, but it is a shunt-style, just like the OEM.

If it might help ease your customer's fears, offer a 6-month warranty on the used SH775. The replacement would be another used SH775, or they could pay the difference for the new one of their choice.

.

[Steve]

Since I was doing some research for my reply, I went ahead and updated my post from a few years ago that did the comparison shopping for a new Polaris R/R.

Click HERE to see that thread.

.

[gsrick]

Since I was doing some research for my reply, I went ahead and updated my post from a few years ago that did the comparison shopping for a new Polaris R/R.

Click HERE to see that thread.

.

I appreciate the info Steve. Just so you can update the info, Bike Bandit gives free shipping on anything over $99.

Reading the Roadstercycle.com home page shows there is a SH847 that is a series R/R that was designed with Suzuki for the VStrom 1000 #32800-31J00 . I think it is also with the Polaris #4012941I have found out they are larger and handle more current.

[Steve]

There might not be any advantage with the SH847. The SH775 is already capable of handling about 30% more than a GS can produce.

.

[posplayr]

Did you get a chance to read my post #17?
That tells why one is better than the other, but not necessarily how they work. Back to basics:

ALL R/R models, regardless of type use diodes. They are the devices that help convert the alternating current (AC) from the stator to direct current (DC) that is needed by the bike. It's actually a pulsed waveform, but it's all on the same side of zero, so it does not change direction. It changes intensity, but not direction. There are three phases in the stator, which allows overlapped waveforms, which evens out the "ripple", so the voltage remains a bit more constant.

ALL R/R models, regardless of type use transistor. What the transistors do will determine whether it is a shunt-type or series-type.
As you have likely heard over and over, when the voltage reaches the setpoint, the OEM shunt-type R/R will SHUNT the excess away from the bike, back through the stator. It now sees the voltage is too low, so it switches the current back to the bike. When it sees that it's too high, it shunts back through the stator and the process repeats. It does this hundreds, maybe thousands of times per second, so the voltage looks rather constant. The problem with this is that the stator is ALWAYS putting out the maximum amount of current that it can. Sometimes it's going to use on the bike, the rest of the time it is being fed back to itself.
A series-type R/R also uses transistors to control the current, but instead of routing it back through the stator, they simply open the circuit to stop current flow. When the voltage drops enough, they close again to allow current flow to the bike. Like the shunt-style R/R, this happens hundreds or thousands of times per second. NO current is re-routed back through the stator. Because the stator actually gets a chance to rest every once in a while, even if it is ever so briefly, it runs cooler.

Both of these R/R styles can use MOSFET transistors. As mentioned in post #17, that will make the R/R run cooler, but it is what those transistors do to the stator current that determines whether the stator can run cooler, too.

Yes, the MOSFET shunt-style R/R can be considered "different from tradtional shunt-type". How? The "traditional" R/R used silicon transistors. The MOSFETs are better than silicon, but that does not make it a series-type R/R.

.

Steve, at the risk of complicating your nice "simplified" explanation, I would caveat your first treatment on all r/r s having diodes. I suspect the compufire does not have any diodes and a shunt mosfet and Sh775 only have 1/2 the 6 diodes you would expect for a full bridge rectifier. This is because rectification can be achived by proper On/off control of the Mosfets. So generally when using a mosfet design, "dynamic rectification" or smart on off timing is used. Iirc early designs seem to retain some diodes in what appears to de a design decision for added safety from shorts.

[Steve]

I appreciate the info Steve. Just so you can update the info, Bike Bandit gives free shipping on anything over $99.

Thanks for the update, I have ammended the list.

Steve, at the risk of complicating your nice "simplified" explanation, I would caveat your first treatment on all r/r s having diodes. I suspect the compufire does not have any diodes and a shunt mosfet and Sh775 only have 1/2 the 6 diodes you would expect for a full bridge rectifier. This is because rectification can be achived by proper On/off control of the Mosfets. So generally when using a mosfet design, "dynamic rectification" or smart on off timing is used. Iirc early designs seem to retain some diodes in what appears to de a design decision for added safety from shorts.

OK. I learn something new every day, can I go home now?

I have more of a "technician" training than "engineer" training, so was unaware of the inner workings. With my background, I was trying to keep it in layman's terms and was building on Rick's understanding: "I know the standard R/R uses diodes(shunt), then they went to diodes and transistors(MOSFET), ..." by saying that they have always had diodes and have always had transistors. Evidently with the newer technology things are changing a bit, but there is still rectification and control, there are just different bits and pieces that are doing the job.

.

[gsrick]

I just thought I'd share the optional series r/r choice especially since it was designed with Suzuki's input.