IVR

gwryder wrote: The IVR circuit is fused at 4 amps, so the power dissapated across the 7805 at that current is 14.2- 5 volts or 9.2 volts x 4 amps =37 watts. Too much for the 7805 even with a good heat sink.

It won't be anywhere near 37 Watts, because 78xx regs are internal limited to 1 A (or 1,5 A for the CV version) and both gauges (fuel and temp) don't even draw half of that. Power dissipation will be in the region of a few Watts. Standard 78xx regs are very, very reliable and for this purpose there is no need to go for 3 A types at all. For gauge panel sanity that 3 A capacity is not such a good idea in case of a short circuit. The reg can dump 3 A over the gauge panels copper traces into the problem and no fuse will blow. Besides.. even if the circuit would draw up to let's say 2 or 3 A in normal circumstances, the more sturdy regulator has to get rid of 2-3 times more heat than a standard 1 A reg would.
I don't remember the current drawn by the gauges (it was 10 years ago), but i do remember it was nicely below the capacity of one standard reg with a small heatsink and bench test showed the regs (I used one for each gauge to spread the heat dissipation) got warm, not hot without heatsink. I have done this conversion on 4 cars ('70 AMX, '73 Javelin, '69 AMX and '71 Hornet) and it has worked perfect ever since. I can't think of any reason why replacing an IVR with a standard 78xx regulator could pose a problem. Worst case scenario would be an internal short to ground in the regulator itself, but the 4 A fuse will take care of that. I have used many thousands (yes really) of those 78xx and 79xx regulators in all packages and capacities and apart from a few that just stopped working for whatever reason, never one single unit shorted.
Calculated, measured, bench tested, proven over the years in a few cars... I say it's a good alternative for IVR's.


Edited by Peter Jan - Jan/03/2013 at 6:34pm

"It won't be anywhere near 37 Watts, because 78xx regs are internal limited to 1 A (or 1,5 A for the CV version) and both gauges (fuel and temp) don't even draw half of that. Power dissipation will be in the region of a few Watts. Standard 78xx regs are very, very reliable and for this purpose there is no need to go for 3 A types at all. For gauge panel sanity that 3 A capacity is not such a good idea in case of a short circuit. The reg can dump 3 A over the gauge panels copper traces into the problem and no fuse will blow. Besides.. even if the circuit would draw up to let's say 2 or 3 A in normal circumstances, the more sturdy regulator has to get rid of 2-3 times more heat than a standard 1 A reg would."

John

RTE makes a plug in solid state IVR(CVR) that fits the 68-70 dash cluster. Check out the IVR4

http://rt-eng.com/rte/index.php/RTE_limiter




Edited by pit crew - Jan/04/2013 at 9:26am

bigbad69 wrote: For most of us, this isn't an issue, but there are a few who have daily drivers and may be out in freezing temperatures.

Good point, though I never saw erratic behaviour down to about -15° C (~5° F). Can't say for lower than that, because that happens here maybe once every 30 years or so.

Thanks Motorhead. I purchased. one from RTE. Works just fine, too...and it has a FLASHING LIGHT!