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Discussion Starter · #1 ·
I just bought the parts to build a 7 volt regulator using the instructions that

Blindstich has at the new site(Thanks again, Stitch) ,I think they came from Reg in Bristol originally.



I was going to attempt to manufacture the unit,, but thought I would read some more on the subject, so I searched the old forum and was reading that you can get a 7807 regulator

that puts out 7 volts without using the LED.



Wouldn't the 7807 be a better and easier fix? Is there a reason that it is not used?

I did not know about the 7807 until after I got back from buying the 7805 so I did not ask if they had one in stock where I bought the one that I got,,maybe they are harder to come by?

Blindstitch, if there is no good reason not to use the 7 volt one, maybe you could edit the thread to include that option. The place where I bought the LED's did not have single 5mm green LED's so I ended up buying a packet of 20 assorted ones @ $6.99.



Also is the heat transfer compound that Reg mentions necessary?
 

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I made one using a zener diode and a pass transistor. I also added a current limit to it so it wouldn't smoke if a wire got shorted. It works fine even though the voltage is 7.2 V. Accuracy is not a problem as there is more variation in the temp sensor as far as absolute resistance at any temp. Using the 5V regulator and the green LED is a cheap way to get the 7V needed. It will vary 0.1 V or more depending on the LED type and over temp. The reason for the 5V over the 7V is the 5V parts are really available and much cheaper. Also the parts self limit if they get too hot or short circuit.



Good luck and don't sweat the small stuff.
 

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I was going to attempt to manufacture the unit,, but thought I would read some more on the subject, so I searched the old forum and was reading that you can get a 7807 regulator

that puts out 7 volts without using the LED.



Also is the heat transfer compound that Reg mentions necessary?


Only thing is you have to order the 7V regulator IC, the one built with the 5V one you can usually find the parts at Radio Shack.



And yes, I'd put a little heat sink compound between the regulator IC and whatever you mount it to, even common silicone grease will do.
 

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Wouldn't the 7807 be a better and easier fix? Is there a reason that it is not used?



Without doubt.

Way back I used a 7805 and green led because I had and have, lots of em knocking about

and in the UK the 7807 was hard to get hold of.

I know a source now but found it would cost me £12 in postage to buy just one

probably the same if I bought10 mind you, but I dont need 10 so Sod that.



7807 is easier and you dont need to insulate the tab fron ground

If you grounded the 7805 with leds tab to ground you'd get 5V



Heatsink?

Deffo !

Luckily most of these IC's have protection circuitry but if you dont heatsink it

you may well find it stops working after while until you recycle the power

Thats what happened when I tried it without.



As for smoothing caps I have never bothered for this curcuit and

havent had one malfunction yet.

All its doing is warming a peice of wire, thats all.

Minor fluctuations or ripple will go unnoticed.
 

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I'm running one of Reg's El cheapo ones in my Main CX.Not hard to make and it works a treat




Remember to get a 5mm Green LED and not a 3MM one otherwise it's not right




PS

Because on UK CXs the regulator is a PITA to get to I just left it in,snipped the yellow wire to use to the IC and taped up the Original Regulator end and the wired it in and stuck it inside my Head light nacelle with some double sided tape making sure that the heat-sink and IC could never ground.
 

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As for heatsinks

I'm currently using a peice of 1/8th ally about half an inch wide

and an inch long

the gauge hasnt shut down due to the IC overheating since and I've probably ridden for

about 2 hours non stop on occaisions so I'd say you dont need to clamp it

to anything too big.

Mind you it is fixed on the outside of my non standard microwave egg cooker

temp gauge holder so I reckon that would help keep it cool

I've also used HSinks that fitted into the original case with the same result

but I drilled a few small holes in the case after potting up to help get a bit of circulation going
 

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Discussion Starter · #11 ·
O.K. Thanks guys,

I would not wanted to have waited to order the 7 volt one in. I used the 7805 and the LED and it works perfectly, it is putting out 7.13 volts or so. I was able to reuse the original regulator case.



Great idea Reg,,although I do not understand how the LED bumps the voltage output by 2 volts,,but then again I don't understand much about electronics
 

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O.K. Thanks guys,

I would not wanted to have waited to order the 7 volt one in. I used the 2805 and the LED and it works perfectly, it is putting out 7.13 volts or so. I was able to reuse the original regulator case.



Great idea Reg,,although I do not understand how the LED bumps the voltage output by 2 volts,,but then again I don't understand much about electronics


I love little cheap stuff like this.I've thanked Reg a few times.Considering the silly prices asked for the real units and if you can get them it's a great little project to make




BTW I think you meant 7805?
 

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Discussion Starter · #13 ·

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Great idea Reg,,although I do not understand how the LED bumps the voltage output by 2 volts,,but then again I don't understand much about electronics


Diodes have long been used as current/voltage regulators and or part of a voltage/current regulation circuit.I've just help fix a M8's 1976 T140v Triumph Bonneville with charging problems.They use a very old system which is a small regulator and a separate Voltage limiting Zener Diode whereas modern machines,ours included,use a combined Regulator/Rectifier.



http://en.wikipedia.org/wiki/Zener_diode
 

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Is there any we can just outright buy at a good price?


Wasn't really used anywhere else, kind of a Honda oddity. How they came up with 7V is a mystery as well.



While the true 7807 is cheap here (call Mouser and ask for a total if sent via USPS) chances are there's bound to be a supplier in other counties that also have them.



Incidentally, a 7805 regulates the input down to 5V above the reference voltage. The ground (center_ pin and the metal tab are considered the reference input. Since you normally ground these it regulates to 5 V above 0 V (GND)



Adding an LED with about a 2.1V drop just raiss that reference level to 2.1V and the IC regulates to 5V + that reference.



This method isn't as stable or accurate as a true 7807 but it's a lot easier for most to find the parts for.
 

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Discussion Starter · #17 ·
I spoke too soon when I said it was working perfectly




The next time I drove the bike the temp gauge was not working.



The strange thing was if I turned the key off and on with the engine hot, the gauge would work,,but when I restarted the engine the needle would drop down again. Turn the key off and on again and back up it would come, until the engine started.



It did work once in a while, maybe 1 out of 5 or 6 tries when the engine was running.



It always worked with the key on/engine off.



I tested the output with the yellow wire unplugged and it always read 7.13V,,but when it was plugged in and the gauge not working there was only 1.5V or so.



When it was plugged in and the gauge was working, it had 7.13V.



I tested the gauge(swapped with a spare I have),,it was the same.

Then I tried another 7 volt regulator from my GL, and the gauge works correctly every time.



I don't know if maybe I got the 7805 too hot when I was soldering it together or if it may have been faulty to start with. The only thing that would be different when the bike was running would be 14 volt input instead of 12 or so when not running. I don't think it was a bad connection because when it worked,it worked fine, not intermittently.



I am going to use the one off the GL for now but when I need one for it I will try to build another and see if I have better luck.
 

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Sounds like you may not have enough heat sink on the regulator IC and it's going into thermal protection. Just remember that if you built the one that uses the LED you can't ground the metal tab of the regulator directly to anything, you have to use an isolation kit for a TO-220 package. Radio Shack should have one of these, it's simply called a TO-220 mounting kit and may even come with a tiny bit of thermal grease although common silicone grease will work. Alternately you can mount the metal tab to a heat sink then make darn sure the heat sink itself never touches anything that's grounded.



The purpose of any heat sink grease (thermal transfer compound) is to greatly improve the heat transfer from the component to the heat sink it's mounted to - even if it's got an insulating washer inbetween. Surfaces that appear flat really aren't, the microscopic roughness of the surfaces is enough to reduce thermal contact to as low as 30% - the thermal grease helps to fill in the voids.



If you can find a 7807 regulator at one of your big electronics supply houses up there it makes things a lot easier. With a true 7807 (less than $1) you can mount the metal tab directly to any metal surface since it's at ground potential instead of being raised by 2.1V due to the green LED.
 

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Discussion Starter · #19 ·
I don't think it is a heat problem,,,it would not work yesterday morning when I first started it. Then once when it was working I drove for about 35 minutes and it was fine.



The heatsink I used was a piece of aluminum just small enough to fit into the original regulator case. It is mounted in the original rubber so there is no way it should be grounding out,,from what I understand if it was grounding the heatsink, it would be putting out 5 volts not 1.5.
 

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I'd try making another one. Did you use a gun or pencil iron while soldering?

I've been using the 7805 with green led for 2 seasons now and no problems. It powers the temperature AND gas gauge on my 500T. It's a nice reliable solution.

I dug out the original potting compound and just attached it inside the original metal case with heat sink compound. Used the original wires and connectors and then finished it off by filling the case with hot glue. Luckily it attaches to fiberglass so I didn't need the isolation kit.
 
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