Motor start capacitor - value ?
robert
British Houston Thompson single phase 1/4hp motor
marked KF TD3205 type BS 2408
The motor start capacitor needs replacing but it has no visible markings
on it due to several paint coatings !
With capacitor removed the motor will run with a hand start and I can
hear what I assume is a centrifugal switch clicking on spin up and spin
down.
Any advice on what size capacitor to buy and try ?
The Natural Philosopher
IIRC about 2.2uF 450V DC or 250v AC is the approved sort of size. For
a sport of one horsepower motor thing.
Rob G
wrote:
Go to a company that does motor rewinding as a supplier (Yellow Pages)
- and of course they will be able to tell you anyway.
Rob
John Rumm
There seems to be quit a variation. The one on my 1hp dust collector was
100uF:
http://www.internode.co.uk/SIP/DSCN5328.JPG
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
The Natural Philosopher
> The Natural Philosopher wrote:
>> robert wrote:
>>> Have acquired an old pedestal drill with a
>>> British Houston Thompson single phase 1/4hp motor
>>> marked KF TD3205 type BS 2408
>>>
>>> The motor start capacitor needs replacing but it has no visible
>>> markings on it due to several paint coatings !
>>>
>>> With capacitor removed the motor will run with a hand start and I can
>>> hear what I assume is a centrifugal switch clicking on spin up and
>>> spin down.
>>>
>>> Any advice on what size capacitor to buy and try ?
>>
>>
>> IIRC about 2.2uF 450V DC or 250v AC is the approved sort of size. For
>> a sport of one horsepower motor thing.
>
> There seems to be quit a variation. The one on my 1hp dust collector was
> 100uF:
>
> http://www.internode.co.uk/SIP/DSCN5328.JPG
>
but it got 'tidied up'.
It isn't that critical., Its just to 'nudge' the motor in the right
direction. Too small and the motor wont start or may start
backwards..that's all.
http://www.remco.co.uk/products/capacitors/Motor_Run_Capacitors_stud_mount.htm
i'll be buggered everything from 1 to 100uF seems to be available.
cynic
A 70 watt burner motor takes a 4 microfarad. Multiplying up a 1/4 hp
should be about 187 watts so try as a beginning 11 or 12 microfarad.
Make sure any cap you try is rated for mains ac. if it helps you could
use 3 of the burner motor caps in parallel. I got mine from Farnell
Components a few years ago
NT
IIRC motor caps need to be rated to higher than mains voltage, typ
600v.
NT
Fredxx
"The Natural Philosopher" <t...@invalid.invalid> wrote in message
news:h8blte$eiq$1...@news.albasani.net...
I would suggest to the OP, that he probably won't go far wrong in choosing a
replacement cap of the same size or volume, assuming that the voltage rating
is the same of course.
It depends on the capacitor construction, it's age, but generally for motor
start capacitors, the value and voltage rating determine the size/volume.
Rob G
> "The Natural Philosopher" <t...@invalid.invalid> wrote in messagenews:h8blte$eiq$1...@news.albasani.net...
>
>
>
> > John Rumm wrote:
> >> The Natural Philosopher wrote:
> >>> robert wrote:
> >>>> Have acquired an old pedestal drill with a
> >>>> British Houston Thompson single phase 1/4hp motor
> >>>> marked KF TD3205 type BS 2408
>
> >>>> The motor start capacitor needs replacing but it has no visible
> >>>> markings on it due to several paint coatings !
>
> >>>> With capacitor removed the motor will run with a hand start and I can
> >>>> hear what I assume is a centrifugal switch clicking on spin up and spin
> >>>> down.
>
> >>>> Any advice on what size capacitor to buy and try ?
>
> >>> IIRC about 2.2uF 450V DC or 250v AC is the approved sort of size. For a
> >>> sport of one horsepower motor thing.
>
> >> There seems to be quit a variation. The one on my 1hp dust collector was
> >> 100uF:
>
> >>http://www.internode.co.uk/SIP/DSCN5328.JPG
>
> > bloody eck. Thats biog that is. I did have one lying round on me desk, but
> > it got 'tidied up'.
>
> > It isn't that critical., Its just to 'nudge' the motor in the right
> > direction. Too small and the motor wont start or may start
> > backwards..that's all.
>
>
> > i'll be buggered everything from 1 to 100uF seems to be available.
>
> I would suggest to the OP, that he probably won't go far wrong in choosing a
> replacement cap of the same size or volume, assuming that the voltage rating
> is the same of course.
>
> It depends on the capacitor construction, it's age, but generally for motor
> start capacitors, the value and voltage rating determine the size/volume.
Same physical size/volume doesn't apply as modern capacitors are very
much smaller for the same capacitance and voltage rating.
YAPH
> robert wrote:
>> Any advice on what size capacitor to buy and try ?
>
>
> IIRC about 2.2uF 450V DC or 250v AC is the approved sort of size. For
> a sport of one horsepower motor thing.
You'll find these in pre-loved (skip grade) central heating circulators
(pumps)
--
John Stumbles -- http://yaph.co.uk
What do you mean, talking about it isn't oral sex?
geoff
<use...@yaph.co.uk> writes
>On Thu, 10 Sep 2009 14:44:09 +0100, The Natural Philosopher wrote:
>
>> robert wrote:
>
>>> Any advice on what size capacitor to buy and try ?
>>
>>
>> IIRC about 2.2uF 450V DC or 250v AC is the approved sort of size. For
>> a sport of one horsepower motor thing.
>
>You'll find these in pre-loved (skip grade) central heating circulators
>(pumps)
>
skip ...
--
geoff
YAPH
> Although the capacitor might well be the reason why the pump is in the
> skip ...
But not likely - most pumps I come across (or put in!) skips are either
surplus to requirements following a boiler swap or have mechanically
siezed up.
--
John Stumbles -- http://yaph.co.uk
I am neither for nor against apathy
geoff
<use...@yaph.co.uk> writes
>On Fri, 11 Sep 2009 20:44:46 +0100, geoff wrote:
>
>> Although the capacitor might well be the reason why the pump is in the
>> skip ...
>
>But not likely - most pumps I come across (or put in!) skips are either
>surplus to requirements following a boiler swap or have mechanically
>siezed up.
>
I used to descale pumps (dozens of the buggers) for a couple of service
companies - about 20% were fine other than that the 2.2u cap had died
so , as I said
--
geoff
John Rumm
You were only seeing the non "I just want of get shot of this unrequired
pump" collection though - i.e. ones people wanted but thought needed
fixing.
geoff
Rumm <see.my.s...@nowhere.null> writes
>geoff wrote:
>> In message <7h036qF...@mid.individual.net>, YAPH
>><use...@yaph.co.uk> writes
>>> On Fri, 11 Sep 2009 20:44:46 +0100, geoff wrote:
>>>
>>>> Although the capacitor might well be the reason why the pump is in the
>>>> skip ...
>>>
>>> But not likely - most pumps I come across (or put in!) skips are either
>>> surplus to requirements following a boiler swap or have mechanically
>>> siezed up.
>>>
>> One might well have thought so except that ...
>> I used to descale pumps (dozens of the buggers) for a couple of
>>service companies - about 20% were fine other than that the 2.2u cap
>>had died
>
>You were only seeing the non "I just want of get shot of this
>unrequired pump" collection though - i.e. ones people wanted but
>thought needed fixing.
>
I doubt they got any further than ringing up and saying that the heating
had stopped working - t'would be the incompetent fitter from the service
company who would take it out
--
geoff
Donwill
third HP) the label says -380W, Cap 75-94 Micro Farad.
The actual capacitor label says 75 micro Farad, 275V
Hope this helps.
Cheers
Don
robert
>>
> On the motor on my Myford ML7, (I would think that it's a quarter or
> third HP) the label says -380W, Cap 75-94 Micro Farad.
> The actual capacitor label says 75 micro Farad, 275V
> Hope this helps.
> Cheers
> Don
starting performance.
nikk...@tiscali.co.uk
start up is the capacitor internally mounted?
The Natural Philosopher
rating or 600V if you can get it.
for 1/4bhp you might get away with even less.
Dozens on ebay.
--
Ineptocracy
(in-ep-toc’-ra-cy) – a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.
harryagain
<nikk...@tiscali.co.uk> wrote in message
news:fedc44dd-079e-4caa...@googlegroups.com...
Induction motors inherently have poor starting torque.
The ones with a capacitor are marginally better and hence will start against
a amall load/run up to speed quicker.
Andrew Gabriel
motor, rather than a capacitor-run motor? The second also gives
a higher running torque, but uses higher grade capacitors.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
The Natural Philosopher
alone..
Tim Lamb
<t...@invalid.invalid> writes
motor: where the LR ratio of a secondary winding gives a small phase
change and does not require a capacitor.
Long while since I actually anything about this:-)
>
>
--
Tim Lamb
Tim Lamb
<t...@marfordfarm.demon.co.uk> writes
>>> motor, rather than a capacitor-run motor? The second also gives
>>> a higher running torque, but uses higher grade capacitors.
>>>
>>He did say something about a centrifugal switch, which suggests start
>>alone..
>
>Umm.. A centrifugal switch could also indicate a simple split phase
>motor: where the LR ratio of a secondary winding gives a small phase
>change and does not require a capacitor.
>
>Long while since I actually anything about this:-)
--
Tim Lamb
koos.b...@gmail.com
Bob Minchin
> I have an ancient table saw with a British Houston Thompson single phase 1.0 hp motor V200-220V. Amp 6.9, RPM 1425, BS170 APPD - the cap is gone and I cant read any values. Any ideas on the cap size??
>
copper windings were cheap. The capacitors were so called ac-
electrolytics and a bit specialised for the application and rarely
marked with a value.
I would not use values from a modern motor as copper is now expensive
and capacitors cheap so the ratios are very different.
Use continuously rated motor run types as these will last longer
If there is any way you can experiment with values, build up from say
10mfd in steps until you get adequate on load starting torque. Be aware
that almost anything will start an unloaded motor. The belts speeding up
from 1425 to respectable saw speeds will impose quite a starting load
If you have pick a value to purchase then maybe 15-20mfd would be a good
guess.
A good source of suitable capacitors to experiment with are the power
factor correction types in old fluorescent lamps which are gradually
being outlawed for the more efficient electric ballast units and so
often found in the scrap.
The other thing to check is if the capacitor has really failed. Other
culprits can be a the centrifugal switches and those early motors are
not usually sealed and dust/dirt can prevent the contacts closing.
Good luck
Bob