MF-135 alternator

[Farmwithjunk]

That's plain bunk... DC current is DC current... doesn't matter to the gauge whether it comes from a battery, an alternator, a generator, or a battery charger.... electrons are electrons....

Biggest difference in the output of an alternator and a dc genset is that most modern alts kick out 37+amps.. and most dc gens kick out 25 or < amps.

An ammeter is a 0 center gauge.. it is used to measure net charge to the battery.. NOT the amperage out of the generator or alternator.

When the electrical system is in a state of discharge, the needle deflects to the negative side of the gauge.. denoting reverse current flow in that wire.. which means the storage battery is providing current to run the electrical load due to a load situation that exceeds the charging systems capability.. or in the case of a non functional chargeing system. A net charge shows up as a positive needle deflection denoting current moving toward the battery, thus charging it.

An Amperage gauge is generall a gauge reading from 0 to? ( 30 or 60 ).. and that is generally used to show total amperage output of a generator or alternator. While both an ammeter and an amperage gauge measure current flow.. thier use is dictated by application.. an ammeter can be use din place of an amperage gauge providing there is sufficient gauge range as to make it usefull.. however am amperage gauge is not a suitable replacement for an ammeter as it cannot show a negative deflection.

A voltmeter can be usefull in conjunction with an ammeter.. but if I could only choose 1.. i'd take the ammeter... tellms me about the state of the battery by looking at the charge rate... a voltmeter can't tell you that as easilly.

My advice to the poster with the odd gauge reading is to check wireing and then replace the ammeter.. they cost about 9$ for a cheapy sunpro. Then.. look for a positive needle deflection on the gauge, and if needed.. the charge voltage on the battery with your vom, or auxilary voltmeter gauge.. etc..


Soundguy

Why is it everyone seems to want a voltmeter? I mentioned in an earlier post that it was the "prefered gauge with most folks". The counter guy at my friendly neighborhood NAPA store was utterly dismayed when I ordered an new ammeter.(Top of the line AutoMeter gauge was only $21) He wanted to know why I wasn't replacing it with a voltmeter "like everyone else does". I can't see why an ammeter is looked down upon by so many. It tells you "CHARGE, NO CHARGE, or DISCHARGE" with one quick look. Almost as simple as an idiot light, but far more informative. From all I can understand, ammeters are all an electrical expert would need in most cases, and all a complete novice would need in most cases.

 

[Soundguy]

Why is it everyone seems to want a voltmeter? I .

I agree...I'm not sure either. I think it is for people that don't know anything about electronics.. I.e. an 'idiot gauge'. The average person (mostly) knows their car/truck/tractor has a 12v battery.. and as long as they see the needle at 12v or above.. they think they are safe.

But they can be wrong. I've seen PLENTY of batteries with 1-2 dieing cells. With the alternator going, the system voltage stayed at charge voltage.. 14.x .. etc.. though the alternator was pumping out extra amps to keep it that way.. as soon as the vehicle turned off.. the bat's would drop to 8v.. and be flat overnight. An ammeter would have told them what was going on... like.. "hey you" your charging at 20A.. even though you have been running for 5 hours... CHECK OUT WHY...

That's why i prefer an ammeter... charge current will tell you lots of things about your battery.. ( as you point out as well ).

Soundguy

 

[jimmysisson]

I second the motion to check all the wiring as if it were suspect. My 135 had a similar intermittent open wire to the alternator - it would charge if you jiggled the wire just so - bad connection to a wireless terminal someone put on. Start from scratch with a wiring diagram. 1974 135 with oe alternator and ammeter - worked fine.
Jim

 

[Farmwithjunk]

I second the motion to check all the wiring as if it were suspect. My 135 had a similar intermittent open wire to the alternator - it would charge if you jiggled the wire just so - bad connection to a wireless terminal someone put on. Start from scratch with a wiring diagram. 1974 135 with oe alternator and ammeter - worked fine.
Jim

One wire..... a 14 ga. wire from the field lug on the regulator to the field terminal on the alternator..... Liked to drove me stark raving mad.

I would take the side panel off, exposing the regulator and wiring, pull the cluster of wires down where I could check everything, and all was well. Shove it back in place to install the cover, and I'd loose field voltage to alternator. No charge. Wire ohmed out when tested. I THOUGHT there was a problem with the regulatorS I was getting. Went through 3 of them. Fortunately, I have a friend in the auto electric business who would let me return the regs for another. I FINALLY gave up and started replacing wires. I replaced the green wire and everything started working. AMEN! When I found the broken stranded copper wire, it seems so simple, yet it never really made itself obvious.

36 year old wire that's spent its life in a harsh environment, surrounded by heat, diesel fuel, dirt, dust, vibration, cow manure, and a half#$$ mechanic doesn't stand a chance. When in doubt, replace.