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blackrose

2 amp fuse blowing

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I've got a manrose 12v extractor fan with a small light inside which draws less than 1 amp. On the same circuit are a couple of led lights so the total draw is about 1.2 amps.

 

The circuit is fitted with a 2 amp fuse and for some reason it keeps blowing fuses when I switch the fan on. It's never happened before in 15 years so is the fan motor getting old and drawing more current or something? 

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8 minutes ago, blackrose said:

I've got a manrose 12v extractor fan with a small light inside which draws less than 1 amp. On the same circuit are a couple of led lights so the total draw is about 1.2 amps.

 

The circuit is fitted with a 2 amp fuse and for some reason it keeps blowing fuses when I switch the fan on. It's never happened before in 15 years so is the fan motor getting old and drawing more current or something? 

Or is the battery getting flatter than normal - that will cause most motors to draw more current.  We had extractor fans on some hire boats and in time they tended to gum up with fat, hair & fluff.

 

I think that you are pushing your luck. Most motors will draw a large starting surge that needs adding to the running current for cable sizing etc. Could you have replaced slow blow fuses with normal ones?

Edited by Tony Brooks

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Bearings in the motor may be wearing resulting in more friction or blades rubbing on the duct, both causing higher amp draw, or as Tony says, a build up of gunk which would increase the load.

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40 minutes ago, Tony Brooks said:

Or is the battery getting flatter than normal - that will cause most motors to draw more current.  We had extractor fans on some hire boats and in time they tended to gum up with fat, hair & fluff.

 

I think that you are pushing your luck. Most motors will draw a large starting surge that needs adding to the running current for cable sizing etc. Could you have replaced slow blow fuses with normal ones?

 

The batteries are fine and the charger is on anyway. It might be getting gummed up with crap. I do hoover it out but that doesn't stop it getting greasy and then the dust sticks to it.

 

Pushing my luck in what way? I don't understand what you mean? With such a small fuse you mean? The circuit is about 10m in total and I think it's about 4mm2 cable. It's a very small load. Should I put a 5 amp fuse in? 

3 minutes ago, PeterF said:

Bearings in the motor may be wearing resulting in more friction or blades rubbing on the duct, both causing higher amp draw, or as Tony says, a build up of gunk which would increase the load.

Could be time for a new fan then.

 

 

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49 minutes ago, Tony Brooks said:

Could you have replaced slow blow fuses with normal ones?

That there is the question I was gonna ask. 

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7 minutes ago, blackrose said:

Should I put a 5 amp fuse in? 

As the fuse is in place to protect the cable (not the piece of equipment) you could put a 30amp fuse in 4mm2 cable and it would still do its job properly.

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5 minutes ago, blackrose said:

 

The batteries are fine and the charger is on anyway. It might be getting gummed up with crap. I do hoover it out but that doesn't stop it getting greasy and then the dust sticks to it.

 

Pushing my luck in what way? I don't understand what you mean? With such a small fuse you mean? The circuit is about 10m in total and I think it's about 4mm2 cable. It's a very small load. Should I put a 5 amp fuse in? 

Could be time for a new fan then.

 

I think what Tony means is that the fuse rating is rather close to the continuous draw of the circuit, and evidently less than the peak/startup current. Yes why not try a 5A fuse, sounds like the wiring can easily take it.

 

If that one blows then yes I’d say time for a new fan, or at least a very thorough cleaning out of it.

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If you can get at the fan blades just give them a nudge and check the fan is still spinning freely. The bearings may have got sticky through drying lubrication, water damage or gunk.

And as others have stated, you could put a heavier fuse and not overload the cable.

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9 hours ago, nicknorman said:

I think what Tony means is that the fuse rating is rather close to the continuous draw of the circuit, and evidently less than the peak/startup current. Yes why not try a 5A fuse, sounds like the wiring can easily take it.

 

If that one blows then yes I’d say time for a new fan, or at least a very thorough cleaning out of it.

Exactly but until we were told the cable seize it would be irresponsible to suggest it.

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1 hour ago, Tony Brooks said:

Exactly but until we were told the cable seize it would be irresponsible to suggest it.

See post 4 for a fairly vague answer.

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31 minutes ago, Slim said:

See post 4 for a fairly vague answer.

Yes, but that was posted after my first reply. I had no idea about cable size when I made my first reply so until the OP later told us  the cable size I had no idea what it was - as I said in my response that you replied to.

  • Greenie 1

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12 hours ago, blackrose said:

I've got a manrose 12v extractor fan with a small light inside which draws less than 1 amp. On the same circuit are a couple of led lights so the total draw is about 1.2 amps.

 

The circuit is fitted with a 2 amp fuse and for some reason it keeps blowing fuses when I switch the fan on. It's never happened before in 15 years so is the fan motor getting old and drawing more current or something? 

Are you sure about the current draw of the light bulb ? I've got a 12v Manrose extractor and it came with a 5w halogen bulb in it.

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51 minutes ago, Tony Brooks said:

Yes, but that was posted after my first reply. I had no idea about cable size when I made my first reply so until the OP later told us  the cable size I had no idea what it was - as I said in my response that you replied to.

Got my tenses wrong , read were as are.😃

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2 hours ago, Flyboy said:

Are you sure about the current draw of the light bulb ? I've got a 12v Manrose extractor and it came with a 5w halogen bulb in it.

5W halogen bulb = 0.4A. Add the motor current and “less than 1 A” is reasonable.

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As a follow up to this, I just put a 5amp fuse in (which in hindsight was the wrong thing to do given that a 2amp fuse was already over-specified); I switched the fan on and it started smoking!

 

Looks like a new fan is in order. Would I have damaged the wiring anywhere?

 

 

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1 minute ago, blackrose said:

As a follow up to this, I just put a 5amp fuse in (which in hindsight was the wrong thing to do given that a 2amp fuse was already over-specified); I switched the fan on and it started smoking!

 

Looks like a new fan is in order. Would I have damaged the wiring anywhere?

 

 

Can't be 100% sure but probably unlikely. I seem to recall the wire is plenty thick enough to be protected by a 5 amp fuse.

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19 minutes ago, blackrose said:

Ok, thanks.

You did say the cable was 4mm2 that's MORE than big enough to carry 5 amps safely without damage.

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I'm looking to buy a couple of these as replacements for the Manrose 12v extractor fans in my galley and bathroom as manrose no longer make them.

 

https://www.ebay.co.uk/itm/12v-24v-Extractor-Fan-Light-DC-Caravans-Motorhomes-Marine-Boat-Ventilation-4/264787240069?hash=item3da68ca485:g:DCkAAOSwbOBfA0ID

 

In the ad it says: 

Please Note: If fan is used while battery is charging please make sure the voltage doesn't increase above 12v or 24v, if the increase is to high the fan will burn out, 

You can use the 24v fan for 12v battery so if you are using while charging and have this issue mentioned above go with the 24v instead of 12v as this will give you the extra voltage needed when attached to the battery

 

Is this advice correct? Wouldn't a 24v fan run at half the speed if connected to a 12v system?

 

 

Edited by blackrose

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That does sound a bit fragile for boat, or motorhome use, if they can't cope with battery charging voltages. Yes a 24V fan would run roughly half speed on 12V. If the 12V fans really are that sensitive, then a 12V to 12V stabiliser like those sometimes used to run sensitive things like televisions might be the thing to get from a 12 to 15V variable supply, with assorted voltage spikes to a stable 12V.

An example, not a recommendation!

Jen

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2 minutes ago, Jen-in-Wellies said:

That does sound a bit fragile for boat, or motorhome use, if they can't cope with battery charging voltages. Yes a 24V fan would run roughly half speed on 12V. If the 12V fans really are that sensitive, then a 12V to 12V stabiliser like those sometimes used to run sensitive things like televisions might be the thing to get from a 12 to 15V variable supply, with assorted voltage spikes to a stable 12V.

An example, not a recommendation!

Jen

 

Thanks. That voltage stabiliser is 4A max, is that correct? Whatever amperage goes in will be what comes out up to a maximum of 4A?

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1 minute ago, blackrose said:

 

Thanks. That voltage stabiliser is 4A max, is that correct? Whatever amperage goes in will be what comes out up to a maximum of 4A?

That is so. I'm not recommending it, just linking to the first example from a search of the Big River Companies on-line emporium to show the sort of thing.

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It would add a lot to the cost of replacing the fans, so I'd look for fans that are not so electrically fragile if it was me.

Jen

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