Boost output voltage on a 7805 regulator
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Re: Boost output voltage on a 7805 regulator
The resistance has to be very very low to reduce the Voltage drops and power dissipation on the meter.
If it is really 0.1 Ohm (did you zero out the meter probes resistance) and you have 30A flowing, the Vdrops will be (E = I x R) = to 30A x 0.1 Ohm = 3V! so with 12V system, the load will only see about 9~10Vdc, and the power dissipation (P = I x E) on the meter will be = to 30A x 3V = 90 Watts! 20A will be 40W.
http://www.sengpielaudio.com/calculator-ohm.htm
Did you verify that the needle is not stuck?Last edited by budm; 06-30-2016, 03:56 PM.Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809Comment
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Re: Boost output voltage on a 7805 regulator
The resistance has to be very very low to reduce the Voltage drops and power dissipation on the meter.
If it is really 0.1 Ohm (did you zero out the meter probes resistance) and you have 30A flowing, the Vdrops will be (E = I x R) = to 30A x 0.1 Ohm = 3V! so with 12V system, the load will only see about 9~10Vdc, and the power dissipation (P = I x E) on the meter will be = to 30A x 3V = 90 Watts! 20A will be 40W.
http://www.sengpielaudio.com/calculator-ohm.htm
Did you verify that the needle is not stuck?
Here's a wiring diagram from cluster to engine harness
Circuit A1-20RD and B1-20BK are for the ammeter.Last edited by Mad_Professor; 07-01-2016, 03:18 AM.Comment
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Re: Boost output voltage on a 7805 regulator
Looks like you should be fine to use a DMM (should still used a fused one) to measure the current. That meter is not taking all of the current (looks like it's only 22? 24? gauge wire winding?), there's another shunt in the schematic that will take the brunt of the current and reduce the total voltage drop. Looks like R6 is the shunt, and it's a piece of 10 or 6 gauge wire depending on what alternator you have. The shunt is fine if you're not getting anything at the meter, likely one of the wires to the meter is bad. You could test your meter with a current limited PSU...Comment
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Re: Boost output voltage on a 7805 regulator
Looks like you should be fine to use a DMM (should still used a fused one) to measure the current. That meter is not taking all of the current (looks like it's only 22? 24? gauge wire winding?), there's another shunt in the schematic that will take the brunt of the current and reduce the total voltage drop. Looks like R6 is the shunt, and it's a piece of 10 or 6 gauge wire depending on what alternator you have. The shunt is fine if you're not getting anything at the meter, likely one of the wires to the meter is bad. You could test your meter with a current limited PSU...Never stop learning
Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956
Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999
Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl
Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/
TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809Comment
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Re: Boost output voltage on a 7805 regulator
stick a 9v battery across it - NOT a lithium one!
btw, with the car battery disconnected, you should meter a very low resistance between the 2 wires in the dash.
if it's not then you have a break in the loom.Comment
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Re: Boost output voltage on a 7805 regulator
Here is an interesting discussion with some actual measurements:
http://webcache.googleusercontent.co...ic.php?t=24551
So I set up a bench power supply for 12V, connected a headlight to it, then cranked the power supply current limit down to 0. I then added the car ammeter in series, and put a clamp-on ammeter on the circuit. I slowly increased the current - and the car ammeter reads full-scale at 0.2 amps. Due to the limited precision of my clamp-on ammeter, this could be anywhere from 0.1A to 0.3A, but at least it gets me in the ballpark.Comment
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Re: Boost output voltage on a 7805 regulator
How about a test?
With the engine off and meter disconnected, turn on the headlamps.
Measure the battery voltage (Vbat) and the voltage between the meter terminals (Vshunt).
Calculate the headlamp current using Plamp x 2 = Vbat x Ilamps, where Plamp is the rated power of one headlamp.
Now Vshunt = Rshunt x Ilamps, so this should allow us to calculate Rshunt.
If the meter goes to fsd at 30A, then Vfsd = Rshunt x 30A.
If fsd occurs at a meter current of 0.2A, then the resistance of the meter should be ...
Rmeter = Rshunt x (30A / 0.2A) = 150 x RshuntLast edited by fzabkar; 07-01-2016, 06:30 PM.Comment
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Re: Boost output voltage on a 7805 regulator
So we took the wrap on the wiring harness off on the engine side of firewall, and found the welded splices and I think a diode of some sort. Not sure what it's for yet, but we hooked up the ammeter to two places where the welded splices were and we were able to see changes on ammeter, with the A/C blower and head lamps on. Our guess is there is a fault between the firewall.
My dad and I are thinking of modding a volt meter inplace of the ammeter.Comment
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Re: Boost output voltage on a 7805 regulator
It's not beyond either of you to figure out- someone put this in, someone can fix it.
Ammeters are more useful too. "At a glance," you get a "picture" of what's going on. A voltmeter either tells you you're not charging, or the regulator ran away...
Ideally, you'd use both.
But no "fireworks," OK? They'd be the wrong kind for the 4th!"pokemon go... to hell!"
EOL it...
Originally posted by shango066All style and no substance.Originally posted by smashstuff30guilty,guilty,guilty,guilty!
guilty of being cheap-made!Comment
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Re: Boost output voltage on a 7805 regulator
*if* the ebay ameters are bidirectional and support the "-" sign, you could use one.
they use an inductive loop.
so you bypass the original shunt resistor, and put the inductive loop over the battery cable.Comment
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Re: Boost output voltage on a 7805 regulator
Which will break the ckt- ammeters go in series and are low impedance. Put a voltmeter there and its high impedance opens the ckt.
It's not beyond either of you to figure out- someone put this in, someone can fix it.
Ammeters are more useful too. "At a glance," you get a "picture" of what's going on. A voltmeter either tells you you're not charging, or the regulator ran away...
Ideally, you'd use both.
But no "fireworks," OK? They'd be the wrong kind for the 4th!
As far as I can see everything is working without the ammeter.
No fireworks, awww you're no fun. What's 4th of july without an electrical fire?
Hmmm interesting, this is really up to my dad, whatever he decides, I'll do it.Comment
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Re: Boost output voltage on a 7805 regulator
Just FYI, here is a kit for a "Compact 0-80A Automotive Ammeter":
http://archive.siliconchip.com.au/cm...1/article.html
http://archive.siliconchip.com.au/st...30551_12mg.jpg
The eBay device would probably be much easier and cheaper to implement.Comment
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