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TR4/4A Question on Voltage Stablizer

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Zimmycobra

Zimmycobra

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Folks:

I have a question for you experienced ones. I have a recently restored 1966 TR4A and I replaced the entire electrical harness with the one from Advance Auto-Wire. It is a great product and everything works well as advertised. Steve's support is fantastic. (But I digress!) The car is negative ground with a new GM alternator as designed into the harness system.

In order to correctly run the original water temp gauge and the fuel tank gauge, I still need to maintain the voltage stabilizer in order to provide the required 10 V to the gauges. I have been using the new electronic versions sourced through Moss Motors. I have had 2 of them totally fail within less than a year. They go to zero output. When I am running, I see about high 14 to 15 V on the volt meter. Is this voltage too high for this stabilizer? Has anyone else had problems with the Moss Motors stabilizers? Nisonger Instruments who is rebuilding my water temp gauge has stabilizers that are a different version, but they are more expensive. Since I trust Nisonger completely (I have a long and very satisfying relationship with Peter Bayer - bought a Contemporary Cobra from him when he owned that company), I may just go with one of theirs next time.

Just hoping to get some opinions/suggestions/comments about this situation. I don't want to keep changing these out every few months.

Thanks.

Zimmy
 
I'm surprised the Moss unit failed, 14-15V should be OK. However, like the homemade ones I typically use, I don't think the Moss units have any input protection for the chip on their circuit board. I can think of two possible causes for the failures you have experienced. My first thought is a transient spike in voltage hitting the stabilizer. You are seeing 14-15V but there could be much higher spikes that you cannot detect on the volt meter. The second possibility is that there may be a periodic dead short on one of the sending unit wires. With a dead short the stabilizer would be called on to deliver at or above its maximum current rating for prolonged times which in turn would result in a failure. The chip would fail long before any damage could/would happen to the sending unit wire.

I am not familiar with Nisonger's product so I cannot comnent if it is better. However, there are a couple of things you can try. I suggest starting with a cheap test. Install on each gauge a 1/2 amp fuse (preferably "slow blow") between a gauge terminal and the sending unit wire. The guages should only draw about 1/3 Amp each when indicating full/hot. If either fuse blows, it indicates a short in one of the sending unit wires. If the fuses do not fail but the replacement stabilizer does fail, that points at either a defective stabilizer or a voltage spike.

For voltage spikes you may want to consider installing a Transient Voltage Suppressor on the power wire going into the stabilizer. I don't know the art to selecting these components but I know they are intended to protect against voltage spikes. They are available from Mouser Electronics (online). Mouser sells to anyone with a credit card and has no minimum purchase amount for orders. You could also buy a handful of 7810 fixed 10V regulator chips from Mouser at the same time. Adding a couple of input capacitors to them would give you your own homemade voltage stabilizer for a fraction of the cost of the Moss or Nisonger units. They are so inexpensive that you could put one 7810 chip on each gauge (which is what I have done on our Spitfire).
 
Doug:

Thanks for the very detailed and in depth response. Some very good suggestions. I will retrace the gauge wires to be sure that there isn't either a short or the potential for one due to wire movement. I do live off a dirt road that has some fairly bumpy sections to get out. Perhaps I have a wire that with the correct jostle hits and shorts somewhere. Can't hurt to look closely again to be sure. Any thoughts on where a transient spike might be coming from if that is the problem?

I like the idea of the 1/2 Amp fuses. I may try that just to protect the stabilizer if it is one of these other issues. Thanks.

Regards:

Zimmy
 
As a side note, the NTE1953 IC regulator I used for my own electronic conversion is internally protected against output short circuit, reverse input voltage, and input transients to 60v. I also added a small tantalum capacitor to the input, which will further help to reduce transients. Dropout voltage is typically only 0.5 volts, so the temperature gauge is still working even when the original generator isn't.

Mouser has the NTE1953 listed for $2.53; I think I paid $3.50 at a local electronics shop.

I don't know what chip the Moss unit uses, but the LM7810 is also protected against output shorts and should tolerate input to 30v.
 
I second the 7810 voltage chip. I put one in for the gauges in my Herald and it is still working about 5 or so years later. I just stuck it in the can from the old regulator. I didn't bother with capacitors or anything else.The chip only has 3 terminals input , output and ground. From the data sheet it looks like they are all safe for inputs of up to about 30 volts and 1.5 amp capacity, way more than you need for two gauges.
 
I have 7810 chips (plural) on the Spitfire gauges. I opened up the hole on the mounting tab so it would fit on the gauge mounting studs. I used one on the temperature and one on the fuel gauge. At less than $1 each it was an inexpensive change. Like 70Herald, I did not use the input our output capacitors and mine have been working for years (10 on the Mini, 4 on the Spitfire). Over the years I have been contacted by several electrical engineers who criticized my article about voltage stabilizers since I did not tell readers to use the capacitors with the chip. For those wanting to use the 7810 chip or the one Randall mentioned, Mouser is a great source for them. If you want to use capacitors to protect the chips, the capacitor ratings needed are listed on the 7810 datasheets and links to the datasheets are available through the Mouser web site.

My article on the voltage stabilizer can be found in the list of files in the link below.
https://sites.google.com/site/purlawson/home/files
 
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