Forums

Motor capacitor value

Started by Jeff Layman June 5, 2016
Maybe SOT, but I think I've seen discussions here before on motors and 
capacitors. Basically, how critical is the capacitance to an electric 
motor (probably start rather than run)?

Background... I have a lawnmower with a 1600w motor. A couple of years 
ago it failed to start, just producing a loud hum and getting  very hot. 
The repair (fortunately still within the guarantee period) stated 
"capacitor replaced".

Last week the same fault appeared - no rotation, just a loud hum. As it 
was out-of-guarantee, I took it apart and found the capacitor - 30uF 
450v. I ordered a new one and fitted it. Unfortunately the motor still 
just hummed. I dismantled the motor and cleaned it, and replaced it and 
the old capacitor. It now works, but I found some mechanical damage on 
dismantling. I might have to replace the motor some time.

On the motor itself I found a label which, amongst rotation speed, 
power, and other things, had "25uF 450v" on it.  So was the original 
repair replacement capacitor at 30uF slightly too high? I see these 
capacitors have a 5% tolerance. Unfortunately I can't find a spec page 
for the motor, but the current replacement (GJC-1600) at 
<http://www.chinahujiang.com/lawn_mower_serial_motors_04.htm> refers to 
a 16ufF capacitor!

-- 

Jeff
I'd say within 10%.  Don't think there's any particular reason for it to be 
more accurate than that.

Does it still run if you give it a spin, then plug it in?  (It needs to 
coast down long enough for you to get your hand out of there, obviously.. do 
this carefully..)

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: http://seventransistorlabs.com

"Jeff Layman" <JMLayman@invalid.invalid> wrote in message 
news:nj0m0i$79e$1@news.albasani.net...
> Maybe SOT, but I think I've seen discussions here before on motors and > capacitors. Basically, how critical is the capacitance to an electric > motor (probably start rather than run)? > > Background... I have a lawnmower with a 1600w motor. A couple of years ago > it failed to start, just producing a loud hum and getting very hot. The > repair (fortunately still within the guarantee period) stated "capacitor > replaced". > > Last week the same fault appeared - no rotation, just a loud hum. As it > was out-of-guarantee, I took it apart and found the capacitor - 30uF 450v. > I ordered a new one and fitted it. Unfortunately the motor still just > hummed. I dismantled the motor and cleaned it, and replaced it and the old > capacitor. It now works, but I found some mechanical damage on > dismantling. I might have to replace the motor some time. > > On the motor itself I found a label which, amongst rotation speed, power, > and other things, had "25uF 450v" on it. So was the original repair > replacement capacitor at 30uF slightly too high? I see these capacitors > have a 5% tolerance. Unfortunately I can't find a spec page for the motor, > but the current replacement (GJC-1600) at > <http://www.chinahujiang.com/lawn_mower_serial_motors_04.htm> refers to a > 16ufF capacitor! > > -- > > Jeff
On Sunday, 5 June 2016 08:59:24 UTC+1, Tim Williams  wrote:
> I'd say within 10%. Don't think there's any particular reason for it to be > more accurate than that. > > Does it still run if you give it a spin, then plug it in? (It needs to > coast down long enough for you to get your hand out of there, obviously.. do > this carefully..) > > Tim
use a flimsy stick not your hand. Plug in and poke it. NT
On 05/06/16 10:20, tabbypurr@gmail.com wrote:
> On Sunday, 5 June 2016 08:59:24 UTC+1, Tim Williams wrote: >> I'd say within 10%. Don't think there's any particular reason for it to be >> more accurate than that. >> >> Does it still run if you give it a spin, then plug it in? (It needs to >> coast down long enough for you to get your hand out of there, obviously.. do >> this carefully..) >> >> Tim > > use a flimsy stick not your hand. Plug in and poke it.
Yes. Before I dismantled the motor I pushed the blade around with a long stick. It soon picked up and rotated at full speed. Now it works without "assistance", but there are some clonking noises coming from the motor when it starts. -- Jeff
On Sun, 05 Jun 2016 08:57:05 +0100, Jeff Layman wrote:

> Maybe SOT, but I think I've seen discussions here before on motors and > capacitors. Basically, how critical is the capacitance to an electric > motor (probably start rather than run)? > > Background... I have a lawnmower with a 1600w motor. A couple of years > ago it failed to start, just producing a loud hum and getting very hot. > The repair (fortunately still within the guarantee period) stated > "capacitor replaced". > > Last week the same fault appeared - no rotation, just a loud hum. As it > was out-of-guarantee, I took it apart and found the capacitor - 30uF > 450v. I ordered a new one and fitted it. Unfortunately the motor still > just hummed. I dismantled the motor and cleaned it, and replaced it and > the old capacitor. It now works, but I found some mechanical damage on > dismantling. I might have to replace the motor some time. > > On the motor itself I found a label which, amongst rotation speed, > power, and other things, had "25uF 450v" on it. So was the original > repair replacement capacitor at 30uF slightly too high? I see these > capacitors have a 5% tolerance. Unfortunately I can't find a spec page > for the motor, but the current replacement (GJC-1600) at > <http://www.chinahujiang.com/lawn_mower_serial_motors_04.htm> refers to > a 16ufF capacitor!
They're not hugely critical, and there's no guarantee that as the manufacturer optimized the thing for price and profit that they may have inadvertently optimized it for longevity, efficiency, an good performance as well. If it's a run cap it might be more critical -- and I could see how a lawnmower might want a run cap and not just a start cap. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!
On 05/06/16 16:43, Tim Wescott wrote:
> On Sun, 05 Jun 2016 08:57:05 +0100, Jeff Layman wrote: > >> Maybe SOT, but I think I've seen discussions here before on motors and >> capacitors. Basically, how critical is the capacitance to an electric >> motor (probably start rather than run)? >> >> Background... I have a lawnmower with a 1600w motor. A couple of years >> ago it failed to start, just producing a loud hum and getting very hot. >> The repair (fortunately still within the guarantee period) stated >> "capacitor replaced". >> >> Last week the same fault appeared - no rotation, just a loud hum. As it >> was out-of-guarantee, I took it apart and found the capacitor - 30uF >> 450v. I ordered a new one and fitted it. Unfortunately the motor still >> just hummed. I dismantled the motor and cleaned it, and replaced it and >> the old capacitor. It now works, but I found some mechanical damage on >> dismantling. I might have to replace the motor some time. >> >> On the motor itself I found a label which, amongst rotation speed, >> power, and other things, had "25uF 450v" on it. So was the original >> repair replacement capacitor at 30uF slightly too high? I see these >> capacitors have a 5% tolerance. Unfortunately I can't find a spec page >> for the motor, but the current replacement (GJC-1600) at >> <http://www.chinahujiang.com/lawn_mower_serial_motors_04.htm> refers to >> a 16ufF capacitor! > > They're not hugely critical, and there's no guarantee that as the > manufacturer optimized the thing for price and profit that they may have > inadvertently optimized it for longevity, efficiency, an good performance > as well. > > If it's a run cap it might be more critical -- and I could see how a > lawnmower might want a run cap and not just a start cap.
I'm sure you are right that it's a run cap. I couldn't see anything externally or internally which would disconnect it after the motor started. FYI, the motor label shows: Ningbo Racing/Hujiang Electric 1116000 230v/50Hz IP00 SI I:c:F 25uF 450v 7.65A P1=1600W 2800 r/min cos &#981;: 0.95 The capacitor is only a couple of cm from the motor and gets very hot after an hour of mowing. It is rated at 85 deg C. It needs to be! -- Jeff
On 5.6.16 20:44, Jeff Layman wrote:
> On 05/06/16 16:43, Tim Wescott wrote: >> On Sun, 05 Jun 2016 08:57:05 +0100, Jeff Layman wrote: >> >>> Maybe SOT, but I think I've seen discussions here before on motors and >>> capacitors. Basically, how critical is the capacitance to an electric >>> motor (probably start rather than run)? >>> >>> Background... I have a lawnmower with a 1600w motor. A couple of years >>> ago it failed to start, just producing a loud hum and getting very hot. >>> The repair (fortunately still within the guarantee period) stated >>> "capacitor replaced". >>> >>> Last week the same fault appeared - no rotation, just a loud hum. As it >>> was out-of-guarantee, I took it apart and found the capacitor - 30uF >>> 450v. I ordered a new one and fitted it. Unfortunately the motor still >>> just hummed. I dismantled the motor and cleaned it, and replaced it and >>> the old capacitor. It now works, but I found some mechanical damage on >>> dismantling. I might have to replace the motor some time. >>> >>> On the motor itself I found a label which, amongst rotation speed, >>> power, and other things, had "25uF 450v" on it. So was the original >>> repair replacement capacitor at 30uF slightly too high? I see these >>> capacitors have a 5% tolerance. Unfortunately I can't find a spec page >>> for the motor, but the current replacement (GJC-1600) at >>> <http://www.chinahujiang.com/lawn_mower_serial_motors_04.htm> refers to >>> a 16ufF capacitor! >> >> They're not hugely critical, and there's no guarantee that as the >> manufacturer optimized the thing for price and profit that they may have >> inadvertently optimized it for longevity, efficiency, an good performance >> as well. >> >> If it's a run cap it might be more critical -- and I could see how a >> lawnmower might want a run cap and not just a start cap. > > I'm sure you are right that it's a run cap. I couldn't see anything > externally or internally which would disconnect it after the motor > started. FYI, the motor label shows: > Ningbo Racing/Hujiang Electric > 1116000 > 230v/50Hz IP00 SI I:c:F 25uF 450v > 7.65A P1=1600W 2800 r/min cos &#981;: 0.95 > > The capacitor is only a couple of cm from the motor and gets very hot > after an hour of mowing. It is rated at 85 deg C. It needs to be!
This has the smell of insufficient AC current rating for the capacitor. Using a starter capacitor for run cap? -- -TV
On 6/06/2016 2:46 AM, Tauno Voipio wrote:
> On 5.6.16 20:44, Jeff Layman wrote: >> On 05/06/16 16:43, Tim Wescott wrote: >>> On Sun, 05 Jun 2016 08:57:05 +0100, Jeff Layman wrote: >>> >>>> Maybe SOT, but I think I've seen discussions here before on motors and >>>> capacitors. Basically, how critical is the capacitance to an electric >>>> motor (probably start rather than run)? >>>> >>>> Background... I have a lawnmower with a 1600w motor. A couple of years >>>> ago it failed to start, just producing a loud hum and getting very >>>> hot. >>>> The repair (fortunately still within the guarantee period) stated >>>> "capacitor replaced". >>>> >>>> Last week the same fault appeared - no rotation, just a loud hum. As it >>>> was out-of-guarantee, I took it apart and found the capacitor - 30uF >>>> 450v. I ordered a new one and fitted it. Unfortunately the motor still >>>> just hummed. I dismantled the motor and cleaned it, and replaced it and >>>> the old capacitor. It now works, but I found some mechanical damage on >>>> dismantling. I might have to replace the motor some time. >>>> >>>> On the motor itself I found a label which, amongst rotation speed, >>>> power, and other things, had "25uF 450v" on it. So was the original >>>> repair replacement capacitor at 30uF slightly too high? I see these >>>> capacitors have a 5% tolerance. Unfortunately I can't find a spec page >>>> for the motor, but the current replacement (GJC-1600) at >>>> <http://www.chinahujiang.com/lawn_mower_serial_motors_04.htm> refers to >>>> a 16ufF capacitor! >>> >>> They're not hugely critical, and there's no guarantee that as the >>> manufacturer optimized the thing for price and profit that they may have >>> inadvertently optimized it for longevity, efficiency, an good >>> performance >>> as well. >>> >>> If it's a run cap it might be more critical -- and I could see how a >>> lawnmower might want a run cap and not just a start cap. >> >> I'm sure you are right that it's a run cap. I couldn't see anything >> externally or internally which would disconnect it after the motor >> started. FYI, the motor label shows: >> Ningbo Racing/Hujiang Electric >> 1116000 >> 230v/50Hz IP00 SI I:c:F 25uF 450v >> 7.65A P1=1600W 2800 r/min cos &#981;: 0.95 >> >> The capacitor is only a couple of cm from the motor and gets very hot >> after an hour of mowing. It is rated at 85 deg C. It needs to be! > > > This has the smell of insufficient AC current rating for the capacitor. > > Using a starter capacitor for run cap? >
Usually start caps have a high uF and lower voltage rating due to the fact they are switched out of circuit after speed has been achieved. From the voltage rating alone that is a run cap and as stated there is no switching gear in the motor.
On Sunday, June 5, 2016 at 12:57:11 AM UTC-7, Jeff Layman wrote:
> Maybe SOT, but I think I've seen discussions here before on motors and > capacitors. Basically, how critical is the capacitance to an electric > motor (probably start rather than run)? > > Background... I have a lawnmower with a 1600w motor. A couple of years > ago it failed to start, just producing a loud hum and getting very hot. > The repair (fortunately still within the guarantee period) stated > "capacitor replaced". > > Last week the same fault appeared - no rotation, just a loud hum. As it > was out-of-guarantee, I took it apart and found the capacitor - 30uF > 450v. I ordered a new one and fitted it. Unfortunately the motor still > just hummed. I dismantled the motor and cleaned it, and replaced it and > the old capacitor. It now works, but I found some mechanical damage on > dismantling. I might have to replace the motor some time. > > On the motor itself I found a label which, amongst rotation speed, > power, and other things, had "25uF 450v" on it. So was the original > repair replacement capacitor at 30uF slightly too high? I see these > capacitors have a 5% tolerance. Unfortunately I can't find a spec page > for the motor, but the current replacement (GJC-1600) at > <http://www.chinahujiang.com/lawn_mower_serial_motors_04.htm> refers to > a 16ufF capacitor! > > -- > > Jeff
Does the motor bearing need lubrication? I found out, *after* I had junked an oscillating fan (but kept the motor pieces!) that all it had needed was some lube on the bearings. Michael
On Sun, 05 Jun 2016 18:44:20 +0100, Jeff Layman wrote:

> On 05/06/16 16:43, Tim Wescott wrote: >> On Sun, 05 Jun 2016 08:57:05 +0100, Jeff Layman wrote: >> >>> Maybe SOT, but I think I've seen discussions here before on motors and >>> capacitors. Basically, how critical is the capacitance to an electric >>> motor (probably start rather than run)? >>> >>> Background... I have a lawnmower with a 1600w motor. A couple of years >>> ago it failed to start, just producing a loud hum and getting very >>> hot. >>> The repair (fortunately still within the guarantee period) stated >>> "capacitor replaced". >>> >>> Last week the same fault appeared - no rotation, just a loud hum. As >>> it was out-of-guarantee, I took it apart and found the capacitor - >>> 30uF 450v. I ordered a new one and fitted it. Unfortunately the motor >>> still just hummed. I dismantled the motor and cleaned it, and replaced >>> it and the old capacitor. It now works, but I found some mechanical >>> damage on dismantling. I might have to replace the motor some time. >>> >>> On the motor itself I found a label which, amongst rotation speed, >>> power, and other things, had "25uF 450v" on it. So was the original >>> repair replacement capacitor at 30uF slightly too high? I see these >>> capacitors have a 5% tolerance. Unfortunately I can't find a spec page >>> for the motor, but the current replacement (GJC-1600) at >>> <http://www.chinahujiang.com/lawn_mower_serial_motors_04.htm> refers >>> to a 16ufF capacitor! >> >> They're not hugely critical, and there's no guarantee that as the >> manufacturer optimized the thing for price and profit that they may >> have inadvertently optimized it for longevity, efficiency, an good >> performance as well. >> >> If it's a run cap it might be more critical -- and I could see how a >> lawnmower might want a run cap and not just a start cap. > > I'm sure you are right that it's a run cap. I couldn't see anything > externally or internally which would disconnect it after the motor > started. FYI, the motor label shows: > Ningbo Racing/Hujiang Electric > 1116000 > 230v/50Hz IP00 SI I:c:F 25uF 450v 7.65A P1=1600W 2800 r/min cos &#981;: > 0.95 > > The capacitor is only a couple of cm from the motor and gets very hot > after an hour of mowing. It is rated at 85 deg C. It needs to be!
It may not have been designed for being used that long -- if you have room, get some air circulation in there, or at least mount the cap away from the motor. That'll keep things cooler and make things live longer. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com I'm looking for work -- see my website!