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DIY Intrument panel voltage regulator mod |
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304-dude 
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Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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 Topic: DIY Intrument panel voltage regulator modPosted: Feb/29/2016 at 8:04pm |
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This will cover most regulators, but I am using a 71 to 74 Javelin regulator in this instruction. I will be adding more for the completion soon... For now here are some disassembly pictures after trimming off the stamped copper contacts from the circuit board. To disassemble, I used diagonal cutters to pry from the corners and scisssor the edge up and away. I just did not have any way to lift the crimp edge on the short sides as the mounting arms and contact legs would get in the way. Note I mounted an insulated tab version of a 7805 TO-220 package 1A 5v regulator, where the adjusting screw that was glued in place after calibration. The adjusting screw was easy to remove and left a near perfect mounting locaton. Having an insulated tab regulator allowed a single sheet metal screw for mounting. As it cuts into the hole just enough to thead it securely. There are TO-220 package mounting kits that consist of a screw and nut with a plastic insulating washer and formica insulator for the body. As long as you mount the IC on the circuit board and it does not touch metal you are fine with just a screw, and if needed a nut as well.  Notice the IC is a used component... one of many that I keep around for various quick and dirty live mods to existing circuits. Thus the legs have been soldering pads to components off and on, so forgive the ugly looking legs. Hehehehehe!  Notice that the cover is being obstructed on the lower right corner. The very corner of the IC is too close to the crimp edge, so I will trim the cover at the corner to allow closure.  Here is how I will wire the IC to the circuit board. Note, that I kept the ground clip that was used for the fine coiled magnet wire, as it is easy to solder to without need of a high wattage iron.  Yep I got these itty bitty AMC striped lables that come in handy. Ha! Now for the IC regulator of choice.... Its a bit over kill but you never know when you'll need reliabliity around 145 degrees C. Hot hot hot... your dash board may melt in your lap, but your gauges will keep on ticking with this one. So it should be safe to say this one can be operated without a heat sink, and installed on the circuit board , that is covered by the metal mounting cover. Ok, I have completed my regulator mod... since I will be modding my low fuel warning relay as well, the standard 7805 regulator will work just fine as it will only be used for temprature gauge use. Thus no more than 500ma max which falls well within operating tolerance. Below at the lower left, shows that I trimmed the corner off of the isolated tab to allow clearance for the cover to close. Yes I did not have any 24awg magnet wire, so I used scrap wire that I thought would handle my 40watt iron. If doing such a thing for resale, I would have gone and bought some and searched for my 25watt iron and capillary tubing in my stored away electronics kit. Half of which had been buried by stuff accumulated through the years. Since I could not keep the wires jacketing from shrinking away, I coated with Goop E6000. I tend to use it on everything.  Notice all I did to close the cover, was to crimp the area that covers the grounding clip. One must be careful not to solder too much on the clip as there is little room to allow the cover to crimp closed. It is best to solder the wire at the end of the clip. When mounted the cover will keep the circuit board secure, so no need to crimp the rest of the tabs.  I have completed my tests, here are my findings... I used a cheap 15 year old digital multi meter so these are ball park figures. No load current is 2.2 ma 1/8 of a tank is 114 ma Full is 200 ma Both fuel and temp gauges DC resistance are between 13 - 14 ohms. So, if your fuel and temp gauges are off by more than 1 ohm there may be some reading errors that can be adjusted by a slight modification. I can cover on if needed. A standard 7805 1 Amp regulator should be good for both temp and fuel gsuge use. If using a ralley pack on a 71 to 74 Javelin, I suggest using the 2.5 amp version listed in the link provided. It will run cooler so no heat sink is required. Since I am using a low fuel warning module, I can use standard 1 Amp regulators in both devices and run a ralley pack without using a heat sink. For those who will perform my mod, I hope you enjoy it as much as I.
Edited by 304-dude - Mar/04/2016 at 8:25am |
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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Rebel Machine
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Joined: Jul/03/2007 Location: Western Il Status: Offline Points: 5122 |
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Posted: Feb/29/2016 at 8:22pm |
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I'd recommend against this. The bi-metallic regulator (which really isn't a regulator) has the ability to disconnect itself quickly, temporarily and repeatedly (via the bi-metallic strip & heater), when there's an excessive current draw. Your 7805 linear regulator will not do this, it will still deliver current which may cause damage to the wiring.
-Steve- |
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304-dude
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Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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Posted: Feb/29/2016 at 8:42pm |
Instrument panel fuse is rsted at 4 amps, which is the smallest fuse on the panel. It is very small and willl pop way before the wiring fails. Though being rated at 1 amp and thst the IC has heat and over current protection, going over one amp will cause the IC to shut down. There is enough room to add a fuse but the new 7805 IC regulators are pretty snazzy, compared to back in the late 70s. I have others that have more features but this one was picked as a test.
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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Lucas660
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Joined: Apr/16/2012 Location: Vic, Australia Status: Offline Points: 1344 |
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Posted: Feb/29/2016 at 10:33pm |
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Peak current for LM78xx regulators is 2.2A. 304 dude is correct in that the watchdog circuit built into the reg will shut down, not pass current. In my 17 years as a electronics tech I have never seen one fail where input shorts to output (as some mosfets can do). I have seen problems where dual tracking supplies in audio gear can go single sided, but this is usually due to heat. The case of the old reg should be adequate with some heat transfer paste, but it may be worth checking current draw. If you are over 700mA I would add a aluminium heatsink. Any more than 1A a different regulator should be used.
Please also note that the TO-220 case is also ground so thermal paste could be used in this case without a mica washer. I think TomJ also has a write up of this exact project on his wps.com site. |
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304-dude
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Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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Posted: Mar/01/2016 at 6:01am |
I will post various 7805 part numbers and their differences to show not all 7805 regulators are the same. As for thermal paste and a heat sink... there is a better way, but requires the IC package to be mounted inside the cover, using the cover as a heat sink, and for better heat capabilities a 2.5A 7805 is available. Its power to heat range is supior to a standard 7805. Since non coated TO-220 packages have ground on the mounting tab, no need for isolating mounting screw to the cover, and soldering a leg to the ground clip. The center leg csn be clipped off in that case. Mounting the IC to the cover should do well, just is a bit of extra work that may not be needed, once I test further with maxium curent and heat, I may decide to move on to the 2.5A version. Just trying the simplest and cleanest way first. |
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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tony matthews
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Joined: Feb/22/2016 Location: england Status: Offline Points: 64 |
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Posted: Mar/01/2016 at 6:47am |
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Hi I'm looking for one that plugs back into the circuit board. appox 1in wide 2 ins length three lugs/spade connectors one at each end facing each other and one sideways.There is a guy selling electronic cvr on this site ,and some other guy said he had an original one but although Iv asked how do I get it in to the UK So far Iv had no reply can you help me or know someone. thanks ..tony
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304-dude
AMC Addicted
Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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Posted: Mar/01/2016 at 7:11am |
Well, I thought things were in order between the convo going on on your topic. Since us Yanks have 6 hour difference, we may be slower at responding with futher info. I think one of them wanted a clean picture to compare with, for an accurate replacement. Some peeps here have to take some time to sort out whst they have, as storage and shop space requires dugging around. Give them 24 hour repsonce time I don't do middle man transactions without first hand knowlege of who I am to work with. Only a few times I have done so, and they were both with someone local. I hope one of them can help, if not you can ask 401Matcoupe, as he may hsve resources.
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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dkrtgood
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Joined: Jun/27/2011 Location: St Pete, FL Status: Offline Points: 1371 |
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Posted: Mar/01/2016 at 7:38am |
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Did the same thing a few years ago, works perfect and you can pick that part up at any radio shack!
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Dave Goodwin
President of Tampa Bay AMC 70 Mark Donohue BBO 390 5-speed 77 Matador Coupe AKA "The Beave" 70 Javelin 360 / Auto - BBG |
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304-dude
AMC Addicted
Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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Posted: Mar/01/2016 at 7:50am |
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Here is a small list of what 7805 devices are available.
L78S05CV. 2A 5V 150 degrees C Minimum operstional voltsge 8V MC7805CT 1.5A 5V 135 degrees C Minimum operational voltage 7.5V LM7805CT 1A 5V 125 degrees C Minimum operational volatage 7V They all have short circuit and thermal protection. Notice as the max current rating drops so does the max temprature rating. The higher the max current rsting the cooler the package operates at half the power capability. Though here is a small price to pay. The higher the current capabilities the higher the minimum operational voltage. In the case for replacing stock regulator operation, such limitation is mute, as 8V is not a problem.
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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304-dude
AMC Addicted
Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9082 |
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Posted: Mar/01/2016 at 8:01am |
Great to hear... I always knew that the mod would work, from various things I have done in the past and seeing older threads on others doing similar things with other manufacturers instrument panel regulators. Back in the late 60s and mid 70s the cost to make a solid state regulator was high compared to using older tech that has already proven its self. Even in the late 70s and esrly 80s it was cheaper to build basic transistor circuit than to use a 7805 IC. As time moved along better tech allowed the improvment of the 7805 IC to be more robust at low cost. If you were inclined to take it further... surfsce mounting a chip for space limitstion would probably work if you had a dual layer PCB to etch and cut into shape for a custom low profile replacement.
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71 Javelin SST body
390 69 crank, 70 block & heads NASCAR SB2 rods & pistons 78 Jeep TH400 w/ 2.76 Low 50/50 Ford-AMC Suspension 79 F150 rear & 8.8 axles Ford Racing 3.25 gears & 9" /w Detroit locker |
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Rebel Machine wrote: