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Alternator or motor?
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Hairyloon



Joined: 20 Nov 2008
Posts: 14983
Location: Today I are mostly being in Yorkshire.
PostPosted: Sat Feb 07, 15 4:59 pm    Post subject:  Reply with quote    

crofter wrote:
Hairyloon wrote:
The Startomatic is a DC system, so it'll be a dynamo, not an alternator.
It has a box full of windings for regulatiion and control, but I can't imagine what would be needed on the dynamo itself.


Lister also made Startomatics producing AC, we used to have one...

In that case, I'd guess that the extra windings you mentioned were to make it a DC motor as well as an AC alternator. I don't think inverter technology was up to much in those days.

RichardW



Joined: 24 Aug 2006
Posts: 8423
Location: Llyn Peninsular North Wales
PostPosted: Sat Feb 07, 15 9:19 pm    Post subject: Reply with quote    

Check the winding wire size in an average starter & compare it to the windings in an alternator.

Hairyloon



Joined: 20 Nov 2008
Posts: 14983
Location: Today I are mostly being in Yorkshire.
PostPosted: Sat Feb 07, 15 11:49 pm    Post subject: Reply with quote    

At a higher voltage you need less current, so don't need such a fat wire.

RichardW



Joined: 24 Aug 2006
Posts: 8423
Location: Llyn Peninsular North Wales
PostPosted: Sun Feb 08, 15 7:21 am    Post subject: Reply with quote    

I would assume that at the lower speed it will be spinning at (unless you are going to gear it down & poss use a slip clutch) it will quickly a, over heat & b, act as a direct short due to the slow speed & burn out the cable just like a stalled / seized motor will.

Ask your self this.

In the ever advancing process of reduction in costs to seek more profits why has no modern manufacture gone down this road?

Hairyloon



Joined: 20 Nov 2008
Posts: 14983
Location: Today I are mostly being in Yorkshire.
PostPosted: Sun Feb 08, 15 7:09 pm    Post subject: Reply with quote    

RichardW wrote:
I would assume that at the lower speed it will be spinning at (unless you are going to gear it down & poss use a slip clutch) it will quickly a, over heat & b, act as a direct short due to the slow speed & burn out the cable just like a stalled / seized motor will.

Why do you suggest it would be spinning slowly? It would be a whacking great big motor compared to the engine.

Quote:
In the ever advancing process of reduction in costs to seek more profits why has no modern manufacture gone down this road?

I can think of a number of possibilities. The first, as already mentioned is that most times, generators tend to be used when there is no mains power available.

RichardW



Joined: 24 Aug 2006
Posts: 8423
Location: Llyn Peninsular North Wales
PostPosted: Mon Feb 09, 15 12:54 am    Post subject: Reply with quote    

Engines tend to be started at slow speeds. IE tick over or less.

vegplot



Joined: 19 Apr 2007
Posts: 21297
Location: Ynys Môn
PostPosted: Mon Feb 09, 15 9:37 am    Post subject: Reply with quote    

What benefits would there be in a universal DC starter motor / generator alternator? It would have to be complex both mechanically and electrically which would impact on cost and long term reliability and well as over efficiency. It probably explains why it's not been done before on a commercial scale.

As I said before torque is going to the major issue. Alternators are high speed low torque devices and therefore it would be impractical (but not impossible but at what cost?) to convert it to a high torque motor.

Dee J



Joined: 22 May 2005
Posts: 337
Location: West Devon
PostPosted: Tue Feb 10, 15 11:56 am    Post subject: Reply with quote    

Dynamos can be made to motor and vica-versa quite easily. The Siba dynastart is not uncommon in the marine engine world and have featured on some older motorcycles and light cars. The advantage of a dc motor or dynamo is that the commutator changes the magnetic fields at the correct times. To achieve the same with an alternator is either to run an open loop system where you drive the alternator with a fixed frequency AC, and hope it picks up and synchronises with it... but you won't get a lot of starting torque... Or set up a closed loop system where the shaft position is detected (rotary encoder) and the drive voltage is sequenced/alternated synchronously... producing better starting torque and control. There are various commercial solutions available http://www.industrial-scientific.com/special_products_division/alternator_drive_technology_kit.htm
amongst others...

vegplot



Joined: 19 Apr 2007
Posts: 21297
Location: Ynys Môn
PostPosted: Tue Feb 10, 15 1:03 pm    Post subject: Reply with quote    

He's probably lost interest now.

dpack



Joined: 02 Jul 2005
Posts: 33990
Location: yes
PostPosted: Tue Feb 10, 15 1:39 pm    Post subject: Reply with quote    

im still watching and learning

if i understand correctly it can be done but it isnt worth the bother as 2 units will each do their job well and a single unit will be awkward doing each as required .

is that right ?

vegplot



Joined: 19 Apr 2007
Posts: 21297
Location: Ynys Môn
PostPosted: Tue Feb 10, 15 1:53 pm    Post subject: Reply with quote    

dpack wrote:
im still watching and learning

if i understand correctly it can be done but it isnt worth the bother as 2 units will each do their job well and a single unit will be awkward doing each as required .

is that right ?


That's my understanding.

dpack



Joined: 02 Jul 2005
Posts: 33990
Location: yes
PostPosted: Tue Feb 10, 15 3:12 pm    Post subject: Reply with quote    

good ,thanks .

Nick



Joined: 02 Nov 2004
Posts: 33825
Location: Hereford
PostPosted: Tue Feb 10, 15 6:50 pm    Post subject: Reply with quote    

vegplot wrote:
He's probably lost interest now.


A+, good work!

onemanband



Joined: 26 Dec 2010
Posts: 1473
Location: NCA90
PostPosted: Tue Feb 10, 15 7:20 pm    Post subject: Reply with quote    

Honda ACG alternator/starter

Hairyloon



Joined: 20 Nov 2008
Posts: 14983
Location: Today I are mostly being in Yorkshire.
PostPosted: Tue Feb 10, 15 10:02 pm    Post subject: Reply with quote    

dpack wrote:
if i understand correctly it can be done but it isnt worth the bother as 2 units will each do their job well and a single unit will be awkward doing each as required .

is that right ?

Possibly, but I think it may be easier to persuade the alternator to run as a motor than it is to fit a motor to an engine that was never designed to have one.

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