amp gauge Question!

[BQS4]

I have changed out the amp gauge on a Sportwagon for just a voltmeter. I'm not removing the large gauge wires that went to the amp gauge, but, my question is, do these two wire still need to be "connected?" The wiring diagram shows that one attaches to the starter via a fuseable link and the other is at the alt. Would not having these two wires connected prevent the car from starting? Attached is a scan from the FSM with the points indicated.

[wrench459]

yes they need to be hooked together or no charging
the amp gauge is a shunt
or you can run a wire from the B+ termail on back of the alt. to the starter
with a fuse link

[tekenaar]

Originally Posted by BQS4 I have changed out the amp gauge on a Sportwagon for just a voltmeter. I'm not removing the large gauge wires that went to the amp gauge, but, my question is, do these two wire still need to be "connected?" The wiring diagram shows that one attaches to the starter via a fuseable link and the other is at the alt. Would not having these two wires connected prevent the car from starting? Attached is a scan from the FSM with the points indicated.

Easiest just to connect those two wires (red/white and red) together on either post of the ammeter, Gene. Safe and takes ammeter out of circuit.

[timemachine]

Gene,

The car will start but it won't charge unless you connect those wires or run a separate circuit. Since it is the charge route from the alternator to battery, I'd connect the terminals with a brass bolt and nut and carefully seal the whole thing in some heat-shrink tubing so it can't accidently ground and spark. You might want to pick up the +12 from somewhere outside this circuit, since it would tell you if your ignition switch or something else is going bad, which is kind of why it's better to have a VM than ammeter. Using the ammeter circuit only checks voltage on that circuit.

Jim

[namba209]

If I read your post right Gene, you've relplaced the ammeter with a voltmeter. If so, then what Otto suggested will work, but you'd have to connect both the wires (Red-Red/White) to the positive connection on the voltmeter and use a separate wire to ground from the negative connection on the voltmeter. It was kinda hard reading the schematic sideways, so I couldn't tell if the voltmeter would be switched or not. If it's like the wiring on the GT the voltmeter would be "on" all the time regardless of key switch position. But it shouldn't drain the battery if it is "on" all the time. HTH.

[2 Fast 4 U]

But if you don't trust it, put a relay in the line that is connected to a switched 12 V circuit

[BQS4]

LOL, just to clarifiy, I didn't replace the amp gauge IN THE CIRCUIT, I just replaced the amp gauge in the rally pod under the dash with a voltmeter. I know that the voltmeter just requires a power source and a ground. It's just that I went to start the car and it wouuldn't. I then checked the wiring diagram and noticed that the amp gauge is connected to the starter. I'll connect the two heavy gauge wires together and seal them up good. Thank you all for your inputs. Proof of the pudding that even though I have been into Opels for 30+ years, I'm still learning.

[tekenaar]

Originally Posted by BQS4 LOL, just to clarifiy, I didn't replace the amp gauge IN THE CIRCUIT, I just replaced the amp gauge in the rally pod under the dash with a voltmeter. I know that the voltmeter just requires a power source and a ground. It's just that I went to start the car and it wouuldn't. I then checked the wiring diagram and noticed that the amp gauge is connected to the starter. I'll connect the two heavy gauge wires together and seal them up good. Thank you all for your inputs. Proof of the pudding that even though I have been into Opels for 30+ years, I'm still learning.

For any ammeter to 'read' correctly, ALL of the load (power using) circuits (red wire) s/b on one side (L) with a single source 12V wire (red/white) direct from the battery to the 'feed' side (+ terminal and actually connected to the + battery cable on the starter solenoid, electrically the same). Any power using wire not connected to the load side will not register its 'draw' (power useage) on the ammeter . . . it effectively bypasses it.

[BQS4]

Just as an update, I found a small brass screw and nut, fastened the two amp wires together, then used a bit of shrink tubing and securely fastened it off under the dash. The car now starts with no problem, thanks all.

[opelspyder]

Understand that full voltage will be running through to your dash and back out, just to run in again. If you are not running an ammeter, remove the wiring and do as suggested to run from alt to starter with wire and fusable link. The reason people remove the ammeters is because to many have fried up or the wiring has melted and grounded out. Its just something that could bite you back in the end
Keith

[timemachine]

Otto,
I'm not sure if I am reading your note correctly but it seems by your terms, the Opel ammeter does not read "correctly" because it only measures the current flow from the alternator to the battery. I think the Opel circuit makes sense because it indicates the viability of the charging system, not the variable load on the alternator caused by lights, ignition, etc. It effectively says that the alternator is meeting the demands of all electrical circuits and keeping the battery charged. If the ammeter remains below zero, the battery is discharging and will eventually go dead (like it does with the engine off and the lights on).

There are lots of nuances to this, and some good reasons to use a voltmeter instead as Gene is doing. We covered a lot of this in an earlier thread:

http://www.opelgt.com/forums/group-1...-ammeter.html?

Also, remember that "full voltage" is always around 14 volts if the regulator is set right, it's the current that varies. A dead or shorted battery will ask for more current and that's what fries the wire in the absense of a fusible link. Separately, cracked insulation or connectors touching ground pulls a lot of current that can start a fire.

Jim

[namba209]

Jim, I'm not sure what the schematics are on Gene's car. If they're anywhere near the GT, full load dishcarge and charge is indicated by the ammeter. Alternator current flow is to the studs in the fuse panel as is the battery's current flow, the ammeter connects the two together, as well as powering all the circuits, either from the battery or the alternator, showing a charge or discharge depending on whether the engine is running or not. As Otto stated and Gene found out, with the ammeter taken out of the circuit,as in disconnecting one or both wires and not connecting them together, nothing will work.

[timemachine]

Ron,

I stand corrected in that the circuit through the ammeter goes through the starter switch to the solenoid that in turn trips the starter circuit (which is separately "hardwired" through the thick + battery cable). So, yes, the car can't start without this shorted.

I can't argue with any of your statements on GTs, I don't have a diagram for that. But here's the Manta Rallye circuit from the factory service manual, hope it shows up well enough. (After you open the thumbnail below, move your mouse from off to onto the image in your IE browser, wait a second and then click on the lower right enlarge icon.)

rallye.jpg

You can see (I hope) that from the alternator (lower left) the output splits, one circuit through the ammeter to the solenoid (and battery +), the other circuit goes to lights and everything else. Since the load returns to the battery through the ammeter and ground, it shows discharge when the engine is off. But, with the engine running, the ammeter by itself tells us only that overall current demands are being met and that the battery is not discharging. It does not tell us how many amps the ammeter is putting out overall, or how much reserve alternator capacity remains. It only tells us what the battery is asking for from the alternator. That's what it was designed for and why I included the thread in my last post on why voltmeters seem to make more sense.

The ammeter circuit when shorted properly could be used to power the voltmeter.

-------red/white-----{bolted together]-----red-------- l
----------------------------l
l
[voltmeter]
l
[ground]

If you do it this way, you'd need to use #10 wire for the connection to the + on the voltmeter as well because of the potential of that circuit. It would be safer and easier to grab the +12 off a lower potential circuit on the fuse bus (or right off the cigarette lighter). But, you can also see in the picture that the fusible link precedes and protects the output of all ammeter current.

Jim

[tekenaar]

Originally Posted by timemachine Ron, I stand corrected in that the circuit through the ammeter goes through the starter switch to the solenoid that in turn trips the starter circuit (which is separately "hardwired" through the thick + battery cable). So, yes, the car can't start without this shorted. I can't argue with any of your statements on GTs, I don't have a diagram for that. But here's the Manta Rallye circuit from the factory service manual, hope it shows up well enough. (After you open the thumbnail below, move your mouse from off to onto the image in your IE browser, wait a second and then click on the lower right enlarge icon.) Attachment 10596 You can see (I hope) that from the alternator (lower left) the output splits, one circuit through the ammeter to the solenoid (and battery +), the other circuit goes to lights and everything else. Since the load returns to the battery through the ammeter and ground, it shows discharge when the engine is off. But, with the engine running, the ammeter by itself tells us only that overall current demands are being met and that the battery is not discharging. It does not tell us how many amps the ammeter is putting out overall, or how much reserve alternator capacity remains. It only tells us what the battery is asking for from the alternator. That's what it was designed for and why I included the thread in my last post on why voltmeters seem to make more sense. The ammeter circuit when shorted properly could be used to power the voltmeter. -------red/white-----{bolted together]-----red-------- l ----------------------------l l [voltmeter] l [ground] If you do it this way, you'd need to use #10 wire for the connection to the + on the voltmeter as well because of the potential of that circuit. It would be safer and easier to grab the +12 off a lower potential circuit on the fuse bus (or right off the cigarette lighter). But, you can also see in the picture that the fusible link precedes and protects the output of all ammeter current. Jim

Electrically, voltmeters are parallel circuits, not series like ammeters, so no worries about wire gauge size. Unlike ammeters, where the entire load (read current) must pass through the device for accurate "reading" on gauge, voltmeters are typically connected to any switched +12V source as they just represent another very small parallel load to the overall electrical circuit. That's why they only require small diameter wires to connect to (not into) the electric circuit. HTH

[namba209]

Jim, you are quite correct, the ammeter on both the GT and Manta schematics show ony what is going in and coming out of the battery, not the total amp draw on the alternator. I had to look real close on my DESTEC schematic to figure that out. I would have scanned the fuse block and let you see how it's wired, but don't want to step on copyright toes (I did talk to JJ Wheatley about this a while back). Both schematics are real close in how they are wired as far as the charging circuit is shown and the power distribution is close too. In order to get a total amp draw indication from the alternator you'd have to wire the ammeter between the alternator and the first junction of the output wire. But then you'd lose the battery amp indication. It's a doggone trade-off. Maybe for optimum system indication, 2 ammeters and a voltmeter could be used.

[timemachine]

Otto,
You are correct to say that the load through the voltmeter is virtually nothing, but if you look at the back of a rallye three gauge console, you'll see that the ammeter circuit 12V+ is also used to power the clock. For the little jumper from the ammeter to the clock+, Opel used the same heavy #10 wire they used for the ammeter circuit itself. That's because a short in that jumper wire would have the same bad effect as a short anywhere in the ammeter circuit. The fusible link would blow much slower than a 5 or 8 amp fuse in the bus and allow a lot of energy, plenty enough to melt a thinner wire and start a fire, through the circuit. That circuit stays on even when nobody is in the car. (Using a light gauge wire off that circuit is the equivalent of plugging a lamp directly into the 200 amp service coming into your house versus through the breaker box. It works, but raises the risk of a meltdown. In house wiring, gauges are related to potential, you use #14 wire for a 15 amp circuit breaker, #12 for a 20 amp circuit breaker etc. You always want the breaker to trip before the wires fail.)

Ron, you're right, an ammeter or two and voltmeter would be a good solution, but I'd be accused of going boy-racer crazy!

Jim

[tekenaar]

Originally Posted by timemachine Otto, You are correct, the load through the voltmeter is virtually nothing, but if you look at the back of a rallye three gauge console, you'll see that the ammeter circuit 12V+ is also used to power the clock. For the little jumper from the ammeter to the clock+, Opel used the same heavy #10 wire they used for the ammeter circuit itself. That's because a short in that jumper wire would have the same bad effect as a short anywhere in the ammeter circuit. The fusible link would blow much slower than a 5 or 8 amp fuse in the bus and allow a lot of energy, plenty enough to start a fire, through the circuit. That circuit stays on even when nobody is in the car. (Using a light gauge wire off that circuit is the equivalent of plugging a lamp directly into the 200 amp service coming into your house versus through the breaker box. It works, but raises the risk of a meltdown. In house wiring, gauges are related to potential, you use #14 wire for a 15 amp circuit breaker, #12 for a 20 amp circuit breaker etc.) Ron, you're right, an ammeter or two and voltmeter would be a good solution, but I'd be accused of going boy-racer crazy! Jim

Correct . . . but those breaker circuits are designed for maximum load (current draw). In your example, it makes no difference if a single light bulb is the only load connected to either the 15 amp or 20 amp cuircuit. With the same 115VAC voltage, current draw (load, resistance) of the light bulb is the same regardless. The amount of current any circuit draws is load (resistance) dependent, not dependent on the maximum rated current available (fused for).

The reason you wouldn't " . . . plug (ging) a lamp directly into the 200 amp versus through the breaker box" has nothing to do with the "200 amp service coming into your house", but everything to do with the 220VAC single phase at that point and the bulb's 110VAC operating voltage. The 220VAC is split into two 110VAC buses at the breaker box, incidently, and that's why there's two rows of breakers there, one for each 110VAC bus bar.

Ohms law: E = IR . . . if voltage (E) and load (R) are constant, the current draw of the circuit also remains constant no matter how much current is actually available to that circuit.

Case in point, when coming to a stop with headlights on, headlights may dim at idle and your ammeter indicates a slight discharge. Headlight load (resistance) is the same, but there is less current available. This will cause less current to flow through the headlight filament (same load, resistance) and result in less voltage (E↓ = I↓R) across the headlight, dimming it.

[namba209]

Originally Posted by timemachine Ron, you're right, an ammeter or two and voltmeter would be a good solution, but I'd be accused of going boy-racer crazy! Jim

Yeah, Jim, I hear that. Must be my USAF mentality coming out. There are so many gages in an aircraft cockpit, that if something went wrong in a system, a "Master Caution" or "Warning" lite would come on, you could then check the annunciator lite panel for which lite was on, then check that gage or gages to see what's whoopin' with that system, then take corrective action, if possible. Maybe a little bit of overkill, but if ignored, could put a big hole in the ground.

[timemachine]

Otto,

I'm not trying to argue and don't want to get into the nuances about house wiring, but I think this is common sense. Everything you say is absolutely correct when things are connected as intended. But, when resistance on the other side of that skinny wire decreases for some reason, (a spade lug slips off and gets near a ground, whatever), that skinny wire draws more current than it is rated for, gets hot, melts, glows or sparks, and the circuit breaker isn't instructed to shut down. It's not just Ohm's Law, it's about the resistance of different gage wires and fuse ratings. Take the metal spring out of a ball point pen, stretch it across the terminals of a dry cell battery and you'll have yourself a nice cigarette lighter.

My rule of thumb under the dash is to never tap into a wire with a lighter gage wire, even for a low-current/high resistance purpose, exactly because of the above.

Jim

[greenopelgt]

Proof that there are no simple answers. WOW!!!!

[timemachine]

Originally Posted by namba209 Yeah, Jim, I hear that. Must be my USAF mentality coming out. There are so many gages in an aircraft cockpit, that if something went wrong in a system, a "Master Caution" or "Warning" lite would come on, you could then check the annunciator lite panel for which lite was on, then check that gage or gages to see what's whoopin' with that system, then take corrective action, if possible. Maybe a little bit of overkill, but if ignored, could put a big hole in the ground.

Ron,

You've just given me a whole new respect for "idiot lights."

Jim

[tekenaar]

Originally Posted by timemachine Otto, I'm not trying to argue and don't want to get into the nuances about house wiring, but I think this is common sense. Everything you say is absolutely correct when things are connected as intended. But, when resistance on the other side of that skinny wire decreases for some reason, (a spade lug slips off and gets near a ground, whatever), that skinny wire draws more current than it is rated for, gets hot, melts, glows or sparks, and the circuit breaker isn't instructed to shut down. It's not just Ohm's Law, it's about the resistance of different gage wires and fuse ratings. Take the metal spring out of a ball point pen, stretch it across the terminals of a dry cell battery and you'll have yourself a nice cigarette lighter. My rule of thumb under the dash is to never tap into a wire with a lighter gage wire, even for a low-current/high resistance purpose, exactly because of the above. Jim

Understand. All good points above, particularly with old, "unknown history" wiring!

[timemachine]

Originally Posted by tekenaar Understand. All good points above, particularly with old, "unknown history" wiring!

A good chat all the way around I think. Glad to see some people still know their Ohm's Law like you do, it's a dying art!

Jim

[namba209]

Originally Posted by timemachine Take the metal spring out of a ball point pen, stretch it across the terminals of a dry cell battery and you'll have yourself a nice cigarette lighter. Jim

Neat trick Jim, I'll have to remember that. I made a similar thing for discharging the surplus military Ni-Cad wet cell batteries I use in my model boat racing stuff. I just hooked up a piece of .032" Ni-Chrome safety wire, through my VOM to both terminals on a battery, slid the VOM lead down the wire until I had a 1 amp draw across the wire and cut it at that point. Then I coiled the wire around a screwdriver shank and put alligator clips on each end and voila, a 1 amp draw across each cell to drain the batteries so they could be recharged correctly. Of course I had to make up 20 of these to drain the batteriy cells individually between race events. One thing I should say, Ni-Cads will get a memory set and need to be discharged totally to erase the memory, then recharged to 140% of total capacity, after they have been charged to 2.0 volts per cell initially. Lotsa work to get a good battery pack, but they will put out 108% of total rated capacity until they are totally discharged, unlike lead acid batteries that will taper off to discharge. Oh yeah, one more thing, you can't use them in cars, they'll go into thermal runaway, which is not a good thing. What happens in that scenario, is the batteries get hot, resistance to current flow drops, they get hotter, resistance goes down more, etc., until they burn up. I should make the point they are used in military applications as an emergency source of power only and are replaced every 120 days and taken to the shop for a battery cell capacity check, bad cells are replaced and made into new batteries packs. Whew, long winded isn't it.

[timemachine]

Ron,

You are way over my head with the ni-cads. I'll leave that to you but take your advice. I discovered the dry-cell trick by complete accident when I was about 10, a typical kid winding toy motor kits, taking his pen apart and coming to the inevitable result. Burned a nice hole in my thumb before I noticed the spring was glowing orange or realized that a 1.5 volt battery could do anything like that. A modern 9-volt battery will probably do the same thing.

Jim