Kyle2
Well-Known Member
The engine in my boat has a Motorola alternator, model no. 9RC 7054. Can anyone tell me if a tachometer can be attached to this, and if so, to what terminal? Thanks for your help.
Can I fit a tacho to Motorola alternator?
- Thread starter Kyle2
- Start date
William_H
Well-Known Member
I don't know specific models of Motorola. However tachos AFIK use an auxilliary terminal a small screw connection on the end opposite the pullley which in your case should be unused. (or it could be another kind of terminal in a plug and socket.
The terminal is actually the centre of the star 3 phase connection which when the alternator is generating produces pulses of about 6 volts 6 to the one turn of the alternator. You need then to calibrate the tacho to the number of pulses you get per engine revolution.
But probably knew all that. Good luck olewill
The terminal is actually the centre of the star 3 phase connection which when the alternator is generating produces pulses of about 6 volts 6 to the one turn of the alternator. You need then to calibrate the tacho to the number of pulses you get per engine revolution.
But probably knew all that. Good luck olewill
VicS
Well-Known Member
[ QUOTE ]
the centre of the star 3 phase connection
[/ QUOTE ] I thought it was from one of the pase coils or a tapping on one coil. But you probabaly know best!
The terminal might be maked W or AC but there is no universal convention on marking alternators.
If there are diffrent ways of providing the output then it will be necessary to use a tacho that is suitable for that particular alternator
BTW I think it is a W on Motorolas
the centre of the star 3 phase connection
[/ QUOTE ] I thought it was from one of the pase coils or a tapping on one coil. But you probabaly know best!
The terminal might be maked W or AC but there is no universal convention on marking alternators.
If there are diffrent ways of providing the output then it will be necessary to use a tacho that is suitable for that particular alternator
BTW I think it is a W on Motorolas
halcyon
Well-Known Member
[ QUOTE ]
I thought it was from one of the pase coils or a tapping on one coil.
[/ QUOTE ]
Yes tapping of one coil. You then need to tie pulses to rev counter, this bit can be fun. We have just had to design a control unit to move the exhaust on a motor yacht from above to below the water at 800 rpm, using a taco pulse from the alternator. This means finding the pulley ratio of the alternator to engine, then you have 8 poles on the rotor, thus engine rpm x pulley ratio x 8 (in our case ) gives pulses per minute, then you convert this.
Isn't life fun.
Brian
I thought it was from one of the pase coils or a tapping on one coil.
[/ QUOTE ]
Yes tapping of one coil. You then need to tie pulses to rev counter, this bit can be fun. We have just had to design a control unit to move the exhaust on a motor yacht from above to below the water at 800 rpm, using a taco pulse from the alternator. This means finding the pulley ratio of the alternator to engine, then you have 8 poles on the rotor, thus engine rpm x pulley ratio x 8 (in our case ) gives pulses per minute, then you convert this.
Isn't life fun.
Brian
William_H
Well-Known Member
Hi Vic well I can't be sure. I had an old 82 Ford (Australian) which had an automatic choke. The choke had a heating element which was driven from the Aux terminal of the alternator.
I might also have recounted the story of an aircaft engineer who fitted a replacement alternator which unlike the original had this extra terminal. He had a spare earth lead so connected that to the spare terminal. When the alternator was switched on (engine running)( for some reason they have an extra alternator on switch in the field circuit) The whole centre of the alternator ie the outer 3 phase coils tried to rotate between the end plates until the wires were torn off the rectifiers. I got involved because he claimed initially that the alternator was badly overhauled. (All these broken wires)
Good luck Vic and Happy Christmas olewill
I might also have recounted the story of an aircaft engineer who fitted a replacement alternator which unlike the original had this extra terminal. He had a spare earth lead so connected that to the spare terminal. When the alternator was switched on (engine running)( for some reason they have an extra alternator on switch in the field circuit) The whole centre of the alternator ie the outer 3 phase coils tried to rotate between the end plates until the wires were torn off the rectifiers. I got involved because he claimed initially that the alternator was badly overhauled. (All these broken wires)
Good luck Vic and Happy Christmas olewill
pvb
Well-Known Member
If it has a W terminal, you connect the tacho to that. If it doesn't have a W terminal, you'll need to connect a wire to the rectifier inside. Take the back off, and you should see a rectifier looking something like this...
Connect the wire to the arrowed terminal. You'll need to find a way of calibrating the tacho so it shows the correct engine speed (there's usually an adjustment screw on the back of the tacho). Sorry it's a lousy picture, but it was the best I could find on t'interweb.
Connect the wire to the arrowed terminal. You'll need to find a way of calibrating the tacho so it shows the correct engine speed (there's usually an adjustment screw on the back of the tacho). Sorry it's a lousy picture, but it was the best I could find on t'interweb.
Kyle2
Well-Known Member
Thanks for your responses. The alternator doesn't have a W terminal, so I will try taking the back off (very, very carefully!!).
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