Why might my alternator/dynamo/thingummy be disconnected? (B7000)

[Deamhain]

Hello all. My first post here. I've looked through a number of posts on the forum around why batteries might not be charging and the like but I think my question is a wee bit different:

First thing - I don't mind a tinker here and there but am not particularly mechanically, or electrically in this case, minded when it comes to vehicles!

I moved to a a wee croft last year and bought an old B7000 for topping the fields and general bits and pieces. It has been grand but, after having to remove and charge the battery a few times I decided to do some reading on the forum. Saw a good post with photos that enabled me to identify the dynamo/alternator/whatever you want to call it. Followed the little bundle of wires that come out of it back to the area of the battery and...

..what I imagine, from it's location and length, to be the wire that would attach to the +ve battery terminal is floating and taped and what looks like a wire of similar physical properties and may well have gone to the -ve terminal has been cut. Not as in accidentally sheared, looks like a very deliberate cut by snips/pliers. There is another very thin blue wire comes out of the wire bundle just behind the switch panel and that has also been left floating.

I haven't stuck a meter across those two thicker wires yet as the battery is out and charging.

Question then: Any ideas why this might have been done? The deliberateness suggests there was a very real reason and makes me wary of just reconnecting - and not knowing what that wee blue wire is strengthens that reluctance. It comes out of the same wiring bundle so must have some relevance. And.. any advice where I go from here - apart from rigging power to the hay shed where the tractor lives and putting it on a maintenance charger!

Thanks for your time folks.
Bob

 

[85Hokie]

Bob

First thing - let see if the dyno is working ......

Should be 2 wires coming from the dyno .... they should have a bullet type connector on the ends that will go to the rectifier. These connectors may be hidden at first glance on the side of the engine somewhere.

Find those two wires - disconnect them - get you multimeter out..... set it TO AC volts (not dc) and start the tractor, warm it up and then place it about 75% throttle.....

take the ends of the multimeter and place them on the two leads - does not matter what color to which one.

DO you get a reading? Should be a number upwards of 25-30 volts AC.

Report back what you come up with!

 

[Deamhain]

Thanks buddy, will do once I get the battery charged. Sounds like a wee job for the weekend!

 

[Old_Paint]

Your hesitance may be prudence.

First of all, getting an electrical diagram and shop manual for your tractor would be the first order of business for troubleshooting. Drawings and shop manuals are the most important tools in your inventory. If the alternator/dynamo is failed, it could present a short circuit to the battery, and light those wires up like a Christmas tree. This is normally bad on anything that runs on any kind of dino-juice. Check the entire length of the insulation of the wiring very closely to make sure it shows no signs of heating anywhere. Insulation will normally blister and bubble if the wire has been too hot.

If you are as novice as you claim, then find someone more qualified that can test the alternator (and rectifier and regulator if they're external) for you. The test described above is a good basic check, IF it truly is an alternator and the external excitation is being applied to the alternator rotor. An alternator's output is regulated by how much current is applied to the rotor which varies the magnetic field produced by the rotor, therefore the voltage output of the alternator. The regulator senses the output (battery terminal voltage) and reduces it if the voltage starts climbing above about 13.8V DC. Raise the voltage above about 14.4 V, and you'll start overcharging the battery, ultimately boiling it dry. This will cause it to be constantly releasing hydrogen as well, so if you smoke, don't do it around a battery. The slightest spark will ignite hydrogen in the tiniest concentrations. Having seen it first hand, I can say that you NEVER want to see or hear a battery explode. It may be indeed that overcharging and failing batteries is the reason yours has been disconnected. If it's a dynamo, it will likely have permanent magnet rotor poles and not need external excitation. They are typically controlled by switching the output on and off with relays as charge is needed by the battery or if the voltage climbs too high. A generator works the same way as a dynamo. The two words actuallly have the same meaning, but are used in different countries. The primary difference is that a generator also usually requires external excitation, but it's output is DC, not AC.

If you can get a Voltmeter on the two wires that are cut, with the engine idling you may answer your own question. If there's no voltage at those wires with the engine idling, it's possible the rectifiers are failed shorted or the windings of the alternator have failed open. If it's AC voltage, that will do nothing to charge a battery, and will in fact discharge it, if it doesn't set the wiring on fire. One failed rectifier (there are usually 3) will discharge the battery. Two normally becomes a short circuit and releases much magical blue smoke. Blue smoke is expensive and hard to find, and extremely hard to put back in when it leaks out. It is the magic of how everything works. I jest with electrical engineering humor, but keep a fire extinguisher VERY handy while troubleshooting electrical problems, and have a way to yank that last wire you connected loose if you smell smoke other than exhaust. The last thing you want to do is set your tractor on fire. When working around the primary battery circuits and charging circuits, they are often unprotected and actually depend on component failure for reliability. Rarely are fuses used in the starting/charging circuits, but on occasion, you will find wiring with fusible links to protect from fires.

More often than not, one of the wires is quite a bit larger than the other(s) and has a much heavier (and usually bolted) connection at the alternator. That would be the charging circuit, or direct connection to V+ at the battery. The much smaller wire is usually the excitation to the rotor (F+). The Common or Earth connection, is normally the housing of the alternator, and usually requires a clean connection through the mounting hardware to make a complete circuit. More often than not, local automotive parts houses will test alternators for free as nearly every car on the planet these days has one, with the possible exceptions of Hybrids and EV's which either run on batteries or a very large alternator that charges very large batteries. They do this because there's normally a regulator, alternator, or battery sale involved, and they're on the clock and might as well have something to do in the eyes of management. It's just good customer relations to provide that service.

If you have a good electrically oriented friend, pick up a couple cartons of your favorite beer, and invite them over for a tinker. Most sparkies love a good beer and an electrical challenge. Better yet, they know exactly what can happen with the wrong wire touching the wrong thing.

 

[Deamhain]

Hi folks,

Couldn't find any in line connections today but it was only a quick look as I needed to be spending time putting fence posts in.

Stuck the multimeter across those two wire ends to see what was afoot. Absolutely nothing is the answer.

Looking like one to be getting in about when there's less other jobs!

Will keep you posted though.

Bob

 

[North Idaho Wolfman]

The 2 connection to the dynamo will be on the front left side.
You need it running and you need the meter to measure AC volts not DC.
You should see 22VAC give or take, if you do the dynamo is working.
Then you'll need to find the rectifier (which by your wording on the wires sounds like it's been cut out).

Pictures of what your working on and what you seeing helps a lot to get to the bottom of these kinds of problems.

 

[GreensvilleJay]

why ? either the dyno is busted,regulator fried, or wires pooched...BUT you need the pulley for the fan belt to work !

Odds are the regulator 'died'
As others have said
1) get a manual or at the very least a wiring diagram(hopefully someone will add a 'link' for you..)
2) confirm 20+ AC volts from the 'dynamo' (alternator....)
3) inspect ALL the wiring ( mice are NOT your friends.....)
4) check the fuse( maybe 10 amps ???)
5) replace the regulator...(B%S style ones will work, bodging the connections)

The circuit is similar to B&S small engine electrical systems....

 

[Russell King]

B&S= Briggs and Stratton =not sure if that engine manufacturer is used in the UK