Your donations help keep this valuable resource free and growing. Thank you.
|
IVR |
Post Reply | Page <12 |
Author | |
gwryder
Supporter of TheAMCForum Joined: Jun/30/2009 Location: Michigan Status: Offline Points: 710 |
Post Options
Thanks(0)
|
Considering the current needed by the gauges, sending unit and the circuit fused at 4 amps, the 7805 is way too small for this application. Consider the specifications state that .5 amps is max and with proper heat sink, only 1.5 amps are max.
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.
I looked through my old Linear Data book and found another 5v regulator (LM323) that's rated at 3 amps and is packaged like the 7805. I'm not sure what the current of the gauge circuits is, but 3 amps might just do it. From the link below, figure 6 looks like the one. I wish I had the time to breadboard this, but if the circuit draw is less than 3 amps it will work. If its more, the application notes says it's bullet proof.
Below is a link to the chips datasheet. This chip appears to be a better solution.
John Edited by gwryder - Jan/03/2013 at 4:56pm |
|
John
70 AMX |
|
Peter Jan
Supporter of TheAMCForum Joined: Nov/10/2010 Location: Belgium -Europe Status: Offline Points: 50 |
Post Options
Thanks(0)
|
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 |
|
Mr AMX
AMC Apprentice Joined: Oct/02/2009 Location: CA Status: Offline Points: 32 |
Post Options
Thanks(0)
|
THANKS ALL!! Yes. Turns out to be a stuck IVR. No 323 in stock, so made a 7805 "tester". Temp gauge worked flawlessly. Hmmmm, should I purchase a solid state $$?? Now, on to dropping the gas tank and see what's up with the fuel sender
|
|
gwryder
Supporter of TheAMCForum Joined: Jun/30/2009 Location: Michigan Status: Offline Points: 710 |
Post Options
Thanks(0)
|
"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."
Peter Jan, you're correct, the 7805 is internally current limited and that limits the power dissipation. However, the 1.5 amps is only with a really good heat sink. If I ever need to replace the IVR, I'll go with the LM323, just because it's far more capable and robust.
John |
|
John
70 AMX |
|
Peter Jan
Supporter of TheAMCForum Joined: Nov/10/2010 Location: Belgium -Europe Status: Offline Points: 50 |
Post Options
Thanks(0)
|
It's more capable and robust, but also capable of dumping more current into a problem that might occur. That's why I would advice not to use higher current types. There's plenty space to mount a TO-220 housing with decent heatsink on the gauges board. TO-3 housing 1A types exist too, they have more "meat" so to speak, they're just not so easy to mount on the gauges board, due to size and how connections are made on that housing.
A few other suggestions to make it "bullet proof" : The choke in series on the board is best left in place, it has current limiting ability when warmed up, especially in case of a short. And to top it off, a well chosen PTC resistor in series, also takes a part of heat dissipation away from the regulator. In my opinion overkill, but it won't hurt a thing. |
|
pit crew
Supporter of TheAMCForum Joined: Jul/08/2007 Location: delete Status: Offline Points: 5341 |
Post Options
Thanks(1)
|
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 |
|
73 Hornet - 401EFI - THM400 - Twin Grip 20 |
|
bigbad69
Supporter of TheAMCForum Joined: Jul/02/2007 Location: Ottawa, Ont. Status: Offline Points: 6686 |
Post Options
Thanks(0)
|
Those RTE units are pretty slick and address a lot of the issues of short circuit protection and input voltage problems. One thing I don't see mentioned on their site is the temperature spec. Common commercial grade components are good from 0-70C. So if you're planning any winter driving, this IVR may not work. (This would also be an issue with the Radio Shack sourced 7805 linear regulator).
Industrial grade parts typically operate -40 to +85C Automotive spec parts are typically -40 to +125C 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. I should also note that the components don't automatically stop working once taken beyond their temperature range. It just means the manufacturer won't guarantee correct operation. The part may continue working just fine, you just don't know if it will or not. |
|
69 Javelin SST BBO 390 T10
|
|
Peter Jan
Supporter of TheAMCForum Joined: Nov/10/2010 Location: Belgium -Europe Status: Offline Points: 50 |
Post Options
Thanks(0)
|
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. |
|
motorheaddad
AMC Apprentice Joined: Jun/21/2012 Location: San Diego Status: Offline Points: 42 |
Post Options
Thanks(0)
|
I bought a solid state IVR from ic237. Worked great and looked professionally made. Good product, good guy
|
|
Mr AMX
AMC Apprentice Joined: Oct/02/2009 Location: CA Status: Offline Points: 32 |
Post Options
Thanks(0)
|
Thanks Motorhead. I purchased. one from RTE. Works just fine, too...and it has a FLASHING LIGHT!
|
|
Post Reply | Page <12 |
Tweet
|
Forum Jump | Forum Permissions You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum |