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 Posted: Sat Feb 12, 2011 8:08 am |
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Joined: Aug 12, 2010
Posts: 190
Trade Rating: 0
Location: Cornwall, UK
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Sure I read somewhere that when alternator is on the way out, they can work in reverse and actually drain current from the battery when the car is parked up. Hence get battery and alternator checked, unless you want to take a chance and get a new battery anyway.
Batteries usually have a code on them. Search online and you can find which of the numbers relate to the battery year code, to see how old yours is.
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Posted: Sat Feb 12, 2011 8:09 am |
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Joined: Feb 07, 2010
Posts: 4455
Trade Rating: +1
Location: Essex
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| V9977 wrote: |
| The disadvantage being that some voltage has to be present in the battery for the alternator to work at all and charge it back up. |
So can you run a car that has an alternator without a battery?
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Posted: Sat Feb 12, 2011 8:11 am |
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Joined: Feb 07, 2010
Posts: 4455
Trade Rating: +1
Location: Essex
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You cry over spilt milk, not cake.
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Posted: Sat Feb 12, 2011 8:14 am |
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Joined: Feb 07, 2010
Posts: 4455
Trade Rating: +1
Location: Essex
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| Werdnal wrote: |
| Sure I read somewhere that when alternator is on the way out, they can work in reverse and actually drain current from the battery when the car is parked up. Hence get battery and alternator checked, unless you want to take a chance and get a new battery anyway. |
Never heard that. I just thought you got both items tested so you replaced the one that wasn't working.
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Posted: Sat Feb 12, 2011 8:18 am |
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Joined: Jan 29, 2011
Posts: 6526
Trade Rating: +10
Location: Westhoughton, Lancashire
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| E5GDM wrote: |
| V9977 wrote: |
| The disadvantage being that some voltage has to be present in the battery for the alternator to work at all and charge it back up. |
So can you run a car that has an alternator without a battery? |
Yes you can. I have known people to change the battery while the engine is running. It saved them having to reset the clock and all the radio stations. Don't know how it would work on a multi-plexed system though.
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Posted: Sat Feb 12, 2011 8:21 am |
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Joined: Aug 12, 2010
Posts: 190
Trade Rating: 0
Location: Cornwall, UK
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| E5GDM wrote: |
| Werdnal wrote: |
| Sure I read somewhere that when alternator is on the way out, they can work in reverse and actually drain current from the battery when the car is parked up. Hence get battery and alternator checked, unless you want to take a chance and get a new battery anyway. |
Never heard that. I just thought you got both items tested so you replaced the one that wasn't working. |
I agree, but I have known people just assume its a duff battery and bung in a new one, only to get the same problem again. Hence always recommended to get both tested and not just assume batt has gone.
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Posted: Sat Feb 12, 2011 8:25 am |
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Joined: Feb 07, 2010
Posts: 4455
Trade Rating: +1
Location: Essex
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| macca1411 wrote: |
| E5GDM wrote: |
| V9977 wrote: |
| The disadvantage being that some voltage has to be present in the battery for the alternator to work at all and charge it back up. |
So can you run a car that has an alternator without a battery? |
Yes you can. I have known people to change the battery while the engine is running. It saved them having to reset the clock and all the radio stations. Don't know how it would work on a multi-plexed system though. |
Thats what i thought, V997's statement don't sound right to me.
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Posted: Sat Feb 12, 2011 8:41 am |
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Joined: Jan 29, 2011
Posts: 6526
Trade Rating: +10
Location: Westhoughton, Lancashire
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| E5GDM wrote: |
| macca1411 wrote: |
| E5GDM wrote: |
| V9977 wrote: |
| The disadvantage being that some voltage has to be present in the battery for the alternator to work at all and charge it back up. |
So can you run a car that has an alternator without a battery? |
Yes you can. I have known people to change the battery while the engine is running. It saved them having to reset the clock and all the radio stations. Don't know how it would work on a multi-plexed system though. |
Thats what i thought, V997's statement don't sound right to me. |
In theory you only require a battery to start the car, but with winter driving where you have the lights, fan, heated rear screen, wipers, radio as well as the normal running of spark plugs and computers, the alternator cannot produce enough current to cope with it all so therefore the battery provides the extra juice and it cannot be replaced. Over time the battery will go flat but 9 out of 10 times it just needs a good overnight charge and everything is OK again. Cold weather can also drain the power stored in the battery as the electrolyte cannot create the chemical reaction required to produce the current.
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Posted: Sat Feb 12, 2011 9:23 am |
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Joined: Mar 09, 2010
Posts: 241
Trade Rating: +1
Location: In a traffic jam
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| E5GDM wrote: |
"There\'s no sense crying over every mistake.\r\nYou just keep on trying \'til you run out of cake".
Don't you mean milk? |
No, cake. Now go play Portal, because you obviously haven't.
(Or just watch this : www.youtube.com/watch?...hZgszykLs)
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| There\'s no sense crying over every mistake.\r\nYou just keep on trying \'til you run out of cake. | |
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Posted: Sat Feb 12, 2011 9:53 am |
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Joined: Feb 07, 2010
Posts: 2949
Trade Rating: +6
Location: Athens, Greece
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| E5GDM wrote: |
| macca1411 wrote: |
| E5GDM wrote: |
| V9977 wrote: |
| The disadvantage being that some voltage has to be present in the battery for the alternator to work at all and charge it back up. |
So can you run a car that has an alternator without a battery? |
Yes you can. I have known people to change the battery while the engine is running. It saved them having to reset the clock and all the radio stations. Don't know how it would work on a multi-plexed system though. |
Thats what i thought, V997's statement don't sound right to me. |
You're right. If the car is already running the exciter coils are driven by the alternator power itself.
So the battery will be charged in that case. My mistake.
It's V9977 though.. 
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| 1.4i, 2001, 3-door, China Blue
Repair safely - Drive safely | |
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