TC-33 electrical nightmare ENDS ! HAPPILY !

[guyw]

In an automotive circuit, fuel injectors work exactly like that: Computer senses amount of fuel required and cycles on/off the injector to meter the amount of fuel as required. The cycling uses a specific on/off ratio (amount of time on vs off) to establish the dwell. In use, injectors consume the most current when they are injecting the most fuel (max on). Using the cycling of the lamp filament as an analogy, the circuit should consume more current when maximum on as compared to cycling such as in a simple bell circuit. I would venture to guess that the windings of an injector would have a greater tendency to arc due to the windings compared to the filament of a lamp. If arcing were to occur due to the cycling function, these computers wouldn't be very reliable because the oscillating circuits are solid state as opposed to relay operated which wouldn't work fast or reliably enough.

Sorry, but I'm still not buying the corroded connection causing blown fuse syndrome. Perhaps someone here would like to take that theory to the test? An experiment of some sort like quickly switching lamps on/off in rapid succession in an attempt to disintegrate a fuse?

But the injector circuit is designed to work that way and the normal operation of the circuit is already designed for with the fuse sizing. In the case of the motor start or the light bulb initial turn on from a cold start, I can assure you that that is the maximum current condition. The on state of the light bulb or the motor up to speed is a lower current condition.

Guy.

 

[Superduper]

The most likely low resistance path(s) back to the negative terminal would probably not be through the fuse.

Guy (Electrical Engineer, ASIC and system design, 27 years ;-) ).

I agree.

In my experience, a bad ground sometimes causes circuits to take weird circuitous routes to find a good ground. A perfect example would be a dual filament tail lamp with a poor ground causing the dash mounted turn signal indicator to light when parking lamps are operated. This occurs because the low beam (parking) filament loses it's ground causing the circuit to continue through the high beam (brake-turn) filament (which shares common but currently bad ground, through the dash indicator bulb filament (that normally operates in turn signal operation) to new ground.

In other words, in the course of finding a new ground, additional resistance is generally added to a series circuit hence lower total current consumption.

 

[Superduper]

Interestingly, going back to the original post, it should be noted that the positive terminal was the bad one and not the negative. Somewhere along the way, bad ground was introduced and a lot has been discussed about bad grounds and it's affect. Anyone care to comment on how or whether this has any affect on the discussion in any way?

 

[RickB]

Interestingly, going back to the original post, it should be noted that the positive terminal was the bad one and not the negative. Somewhere along the way, bad ground was introduced and a lot has been discussed about bad grounds and it's affect. Anyone care to comment on how or whether this has any affect on the discussion in any way?

Yes, there's more typing than reading or thinking going on here...........

 

[guyw]

Interestingly, going back to the original post, it should be noted that the positive terminal was the bad one and not the negative. Somewhere along the way, bad ground was introduced and a lot has been discussed about bad grounds and it's affect. Anyone care to comment on how or whether this has any affect on the discussion in any way?

As far as a starter blowing the fuse due to lower initial voltage causing a longer initial current draw, a bad (higher resistance) positive battery terminal connection should have the same affect as a bad (higher resistance) negative battery terminal connection.

Guy.

 

[RickB]

As far as a starter blowing the fuse due to lower initial voltage causing a longer initial current draw, a bad (higher resistance) positive battery terminal connection should have the same affect as a bad (higher resistance) negative battery terminal connection.

Guy.

The fuse in question is totally unrelated to the starting circuit.

 

[guyw]

The fuse in question is totally unrelated to the starting circuit.

Went back and re-read original post. You are correct. It was the fuse for the lights that was blowing. Should have been more careful with my response. However, same thing applies for light bulb inrush current as motor start up (or motor stall for that matter). When the lights are cold and just starting to light up, they will have their lowest resistance and therefore largest current draw. If the initial voltage is too low for them to heat up to normal operating temperature and normal operating resistance in a timely matter, the fuse could blow. To answer Superduper's question, either a bad negative connection or a bad positive connection resulting in a lower initial voltage would give similar results.

Guy.

 

[Keoke]

Yes, or the solenoid is being repeatedly energized and de-energized at a very high rate due to a dirty contact making intermittent contact within the switch or relay. Think of it like a light bulb in a room. Is that bulb going to last long if you stand at the switch and rapidly switch it on and off? Chattering relays and dirty switches with contact bounce can cause problems, especially in circuits where the protection (fuse) is not rated much higher than the maximum normal load.

I suspect that when the engineer(s) designed the TC33 ignition, he (they) did not expect contact failure or degradation to be a problem. In hindsight, they did not design the circuit properly to account for degradation. That's just my opinion because I would have to do extensive testing of lots of tractors to prove my theory. Sometimes it's easier to come up with a stable workaround solution than to figure exactly all the relay timing and the static and dynamic loads within a circuit. Not only that, but what if a relay has sticking contacts that don't release as they should to switch from normally-closed to energized-open? The mind boggles at the possibilities...

Folks, the starter solenoid has two windings, the pull in winding (hi amps) and the holding winding (low amps). They go on at the same time but the pull in winding is B plus-ed at both ends when the heavy solenoid contacts are bridged and thus pulls no current when the starter starts to rotate.
The starter, as was said, pulls hi initial current that drops off when its armature starts to pick up speed and generate CEMF (an opposing voltage).
It takes hsp (746 watts=1hsp) to turn a starter. A slightly weak battery (low voltage) will cause starter to possibly draw a little more amps then a strong one because the missing voltage will be made up with more amps. EG. a 6 volt starter will draw more amps then a 12 volt starter on the same engine (IXE= P) so if the same hsp is needed and the voltage is less then amps must be used to make up the needed watts. We are talking motors here not restive loads (light bulbs). This is why 6 volt battery cables are fatter then 12 volt cables.
Also, a common fault when when trouble shooting blown fuses is doing the current measuring (or fuse choice) with the engine off. When doing this all loads are operating at battery voltage (12.6) or lower and the current draw may look to be within the range of the fuse. However, when the vehicle starts the voltage goes up (13.8 to 14.8) and consequently the current flow may now go up to a level that exceeds the chosen fuse. Bottom line, all load measurements should done at dynamic voltage (engine running).
As far as an intermittent ground blowing fuses, only if there is a coil winding (relay, solenoid, motor, etc.) in the circuit affected, it is possible that the intermittent (sudden complete off/on) can cause a spike voltage from the coil into the circuit and thus a surge current which could then blow the fuse. This, however, would be rare event and a long-shot at best.

take care,

 

[RickB]

A slightly weak battery (low voltage) will cause starter to possibly draw a little more amps then a strong one because the missing voltage will be made up with more amps.



However, when the vehicle starts the voltage goes up (13.8 to 14.8) and consequently the current flow may now go up to a level that exceeds the chosen fuse.

That reads like you want to have it both ways. The first statement is true; the second is not.

 

[Keoke]

That reads like you want to have it both ways. The first statement is true; the second is not.

Rick, both statements are correct. In a circuit with a fixed resistance load (lighting) if the voltage is increased from 12.6 to 14.6 the current will increase proportionally when all the conductors, including bulb filaments, have reached a stabilized operating temperature.
EG. 12E/2R= 6 amps vs 14E/2R= 7 amps.
Hooking up a 110v light bulb to a 220v circuit will roughly double the amp flow through the circuitry giving you toast as a result.

Jinman, relay chattering is very seldom the fault of the relay itself and is usually caused by fluctuating operating voltage drop across the relay. If we had 5 cents for every relay that was replaced because of this chattering we would both be very rich. I will try to explain. When you hit the start button current flows through relay winding pulling the contractor down. This then causes current to flow to the load (starter). At this point the relay has to share the available voltage with the load (starter) this causes the voltage across the relay to drop to the point where the magnetic field or pull down current is not strong enough to hold contacts down. This in turn causes the relay spring to open contacts and take starter draw out which then brings on a rise in voltage across the relay allowing it to close again. This cycle is repeated very rapidly causing this chatter.
The usual causes of low operating voltage across relays/starter solenoids are:
1. Low battery voltage under load
2. Excessive resistance on hot side of circuit under load
3. Excessive resistance on gnd side of circuit under load

Hey guys, I hope the above makes some sense, but if it doesn't I understand.

cheers,