stillp Posted August 19, 2022 Report Share Posted August 19, 2022 This is rather ironic, since many years ago I was named on a patent for the use of solid-state voltage regulators for car instruments. When the original IVS in my 4A failed I replaced it with a home made one using a 7810 regulator IC and a small capacitor to protect the 7810 from spikes. I've had to replace the IVS occasionally - every few years, so the failures haven't been a problem. However, after my saga with the screen wipers and washers, the IVS failed - I replaced it, and the replacement failed almost immediately. I made and fitted another, and that failed as soon as I went for a test drive. Three failed regulators within a week - can anyone think of a possible cause, or have I just bought a bad batch of 7810 regulator ICs? All the earths are good, and the battery voltage is OK. I still use a dynamo so the charge is a bit spiky, but before the problem with the wipers the IVS had lasted several years. I've now fitted an electromechanical one with a fuse between the output and the instruments, in case there's an intermittent short-circuit after all my messing around behind the dashboard. If the fuse blows it'll be glove box out time! Pete Quote Link to post Share on other sites
RobH Posted August 19, 2022 Report Share Posted August 19, 2022 (edited) I thought the 7810 had plenty of internal protection Pete, including for short circuit so maybe it is a duff batch? I'm surprised you've had to replace them as frequently as every few years though - after all it is not working very hard in that application. Perhaps the supply is spikier than you think - I seem to remember someone had used a 'scope and seen very large ignition spikes, so a small capacitor may not be adequate on its own. Maybe a series inductor is required too, or even a varistor? Edit - just a thought but the stabiliser is used as the pick-off point for supply to the wipers etc so any nasties they are creating will directly affect the input to the stab. Edited August 19, 2022 by RobH Quote Link to post Share on other sites
Lebro Posted August 19, 2022 Report Share Posted August 19, 2022 TVS (transient voltage supressors) are very good at protecting electronics, available in a range of voltages, & power capabilities. Used them a lot when designing electronic devices for marine use, which had to pass some pretty tough EMC tests Bob Quote Link to post Share on other sites
John Morrison Posted August 20, 2022 Report Share Posted August 20, 2022 is A voltage stabaliser unit (original not solid state type) testable on the bench? John. Quote Link to post Share on other sites
Charlie D Posted August 20, 2022 Report Share Posted August 20, 2022 (edited) 10 hours ago, RobH said: Just a thought but the stabiliser is used as the pick-off point for supply to the wipers etc so any nasties they are creating will directly affect the input to the stab. Pete, Every time the unit blew had you been using the wipers and/or the washers previously? If not I guess you could rule them out of the equation. (Just for the record I use a 7810 on my 3A and many other projects over the years and never bothered with capacitors. Never had a failure.) Charlie Edited August 20, 2022 by Charlie D Quote Link to post Share on other sites
Lebro Posted August 20, 2022 Report Share Posted August 20, 2022 2 hours ago, John Morrison said: is A voltage stabaliser unit (original not solid state type) testable on the bench? John. Yes, but not with a digital meter, you could use an old fashioned analogue meter, or an ocsciloscope. Bob Quote Link to post Share on other sites
john.r.davies Posted August 20, 2022 Report Share Posted August 20, 2022 I beg to disagree! The 'oscillation' between zero and battery volts is quite slow, 2-3 Hertz (two or three times a second) which a digital can easily follow. Quote Link to post Share on other sites
stillp Posted August 20, 2022 Author Report Share Posted August 20, 2022 13 hours ago, John Morrison said: is A voltage stabaliser unit (original not solid state type) testable on the bench? John. Yes, but it needs a load so the current in the heater is enough to make it work. Sorry, I don't know how much current the instruments take, but it must be less than 1 Amp. Pete Quote Link to post Share on other sites
stillp Posted August 20, 2022 Author Report Share Posted August 20, 2022 My traditional type (thermal) IVS behaved during three hours or so of driving to Ambergate and back today, and the inline fuse I fitted didn't blow, so there probably isn't a wiring fault and therefore I probably have a faulty batch of 7810 regulator chips. 10 hours ago, Charlie D said: Pete, Every time the unit blew had you been using the wipers and/or the washers previously? If not I guess you could rule them out of the equation. (Just for the record I use a 7810 on my 3A and many other projects over the years and never bothered with capacitors. Never had a failure.) Charlie Thanks Charlie, that might explain the first failure, which occurred after a week changing the wiper rack and wheelboxes, but not the second two. I don't remember using a capacitor when we were developing the one for Ford, but in that case the 7810 was fitted directly to the printed circuit that connected the instruments, so there was probably some transient protection on that board. Pete Quote Link to post Share on other sites
Lebro Posted August 21, 2022 Report Share Posted August 21, 2022 12 hours ago, stillp said: Yes, but it needs a load so the current in the heater is enough to make it work. Sorry, I don't know how much current the instruments take, but it must be less than 1 Amp. Pete Have to disagree there. The heater current is from the units output to earth, not via the load (gauges). Bob Quote Link to post Share on other sites
stillp Posted August 21, 2022 Author Report Share Posted August 21, 2022 Yes, I agree Bob. Pete Quote Link to post Share on other sites
ed_h Posted August 21, 2022 Report Share Posted August 21, 2022 Here is what the output waveforms look like for an original thermal stabilizer. Ed Quote Link to post Share on other sites
stillp Posted August 26, 2022 Author Report Share Posted August 26, 2022 At Ambergate a nice chap in the autojumble section sold me a TR7 IVS, which, instead of the three terminals I'm used to, has four: E, B, T, and L. E and B are presumably Earth and Battery. We thought the latter two might be for Temperature and fueL, but on the TR7 wiring diagrams I've found online, all the instruments are connected to the same source. Does anyone know what the T and L terminals are for? Pete Quote Link to post Share on other sites
RobH Posted August 26, 2022 Report Share Posted August 26, 2022 I think you need to read this old thread Pete. The TR7 has no voltage stabiliser as this shows - what you have bought might be a low fuel delay unit: Quote Link to post Share on other sites
stillp Posted August 26, 2022 Author Report Share Posted August 26, 2022 Interesting thread Rob, thanks. Lucky I didn't pay much for it. Pete Quote Link to post Share on other sites
stillp Posted September 6, 2022 Author Report Share Posted September 6, 2022 On 8/26/2022 at 6:42 PM, stillp said: At Ambergate a nice chap in the autojumble section sold me a TR7 IVS, which, instead of the three terminals I'm used to, has four: E, B, T, and L. E and B are presumably Earth and Battery. We thought the latter two might be for Temperature and fueL, but on the TR7 wiring diagrams I've found online, all the instruments are connected to the same source. Does anyone know what the T and L terminals are for? Pete Well it tested out OK, and the TR7 drivers I know aren't interested, so I put it on ebay. https://www.ebay.co.uk/itm/125499848535 Pete Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.