Is there any way to work out what size alternator is needed to satisfy extra electrics added to a vehicles electrical load.
This is what I have.
LC running a 202 with the following extra stuff:
VK EFI setup (inc. computer, injectors & sensors)
Electric EFI fuel pump
Electric carter carby lift pump
Davis Craig DC31 Thermo fan
Electronic dizzy
At the moment I'm still using the std Bosch 35 amp alternator and not surprisingly the amp meter is always on full charge and the battery still slowly runs flat.
What size should I use and how do I connect it up (as far as regulator etc. goes)??
Cheers
Alternator - what size?
Started by
_whiteLC_
, Jul 18 2006 09:23 PM
17 replies to this topic
#2
TerrA LX
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Posted 18 July 2006 - 09:50 PM
what amps on full is your amp meter reading?
#3
_whiteLC_
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Posted 18 July 2006 - 10:02 PM
30 amps. GTR dash. The needle goes hard over though, it will drop back a little if I stick the headlights on though.
#4
gtrboyy
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Posted 18 July 2006 - 11:17 PM
I would grab a v8 vs alternator as it bolts up to the 6 & 8 brackets,I think it's about 85A but there is the cop one that has 110.There was a thread on this somewhere with the part number.
white wire to + of battery
brown wire to alt light
& power wire of alt stud to + of battery or starter motor stud if battery in boot.
white wire to + of battery
brown wire to alt light
& power wire of alt stud to + of battery or starter motor stud if battery in boot.
#5
Dr Terry
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Posted 19 July 2006 - 08:50 AM
Hi Guys.
whiteLC said " and not surprisingly the amp meter is always on full charge and the battery still slowly runs flat."
This can't be correct. The ammeter is showing that the battery is being charged, if it wasn't then the ammeter would be show a discharge.
The ammeter, if wired correctly, shows the current that is entering (or leaving) the battery itself, while the motor is running.
Either the ammeter is not telling the truth, because it's wired wrongly, there is some other drain when the motor is not running or the battery is cactus.
Having said all of that, a 35 amp alternator is too small for an EFI car. As one of the others said, fit an 85 amp unit off a late model Commodore.
Dr Terry.
whiteLC said " and not surprisingly the amp meter is always on full charge and the battery still slowly runs flat."
This can't be correct. The ammeter is showing that the battery is being charged, if it wasn't then the ammeter would be show a discharge.
The ammeter, if wired correctly, shows the current that is entering (or leaving) the battery itself, while the motor is running.
Either the ammeter is not telling the truth, because it's wired wrongly, there is some other drain when the motor is not running or the battery is cactus.
Having said all of that, a 35 amp alternator is too small for an EFI car. As one of the others said, fit an 85 amp unit off a late model Commodore.
Dr Terry.
#6
_devilsadvocate_
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Posted 19 July 2006 - 09:54 AM
As Dr Terry has pointed out ^, how the ammeter is connected is important, you may have not done anything to it but connected other items in other places.....
The ammeter in the standard setup measures the net current movement through the battery. If the alternator output matches what is needed for all the necessary loads and accessories the needle stays in the middle to indicate that no net current is being demanded of the battery. In fact the needle should sit just to the right to indicate that there is always a small charging current going through the battery....one sees that when the battery is discharged that the needle should move further to the right.
If accessories are added to the +ve of the battery or the starter, such as fans, fuel pumps by relays etc, then the current for them will also need to flow through the ammeter, showing the needle sitting on the right of centre when these accessories are used with the motor running. Using the standard accessories should see the needle move to the left, as you witness when using the headlamps.
To have the ammeter operate as intended, connect all accessories to the the alternator directly rather than the +ve of the battery. One could also overload the ammeter if running a lot of high powered accessories otherwise
Is the 35A alternator enough, possibly not at idle, where its output is only ~18A, if electric fans fuel pump, efi , headlights, heater fan are all in use.
To use your ammeter to work this out, rewire the accessories to the ammeter as ^ and observe where the ammeter sits at idle and indeed at higher rpm when all the loads are in use. This should give you some idea on how much more alternator you will need, but given your battery is already getting run down, perhaps you do need more.
The ammeter in the standard setup measures the net current movement through the battery. If the alternator output matches what is needed for all the necessary loads and accessories the needle stays in the middle to indicate that no net current is being demanded of the battery. In fact the needle should sit just to the right to indicate that there is always a small charging current going through the battery....one sees that when the battery is discharged that the needle should move further to the right.
If accessories are added to the +ve of the battery or the starter, such as fans, fuel pumps by relays etc, then the current for them will also need to flow through the ammeter, showing the needle sitting on the right of centre when these accessories are used with the motor running. Using the standard accessories should see the needle move to the left, as you witness when using the headlamps.
To have the ammeter operate as intended, connect all accessories to the the alternator directly rather than the +ve of the battery. One could also overload the ammeter if running a lot of high powered accessories otherwise
Is the 35A alternator enough, possibly not at idle, where its output is only ~18A, if electric fans fuel pump, efi , headlights, heater fan are all in use.
To use your ammeter to work this out, rewire the accessories to the ammeter as ^ and observe where the ammeter sits at idle and indeed at higher rpm when all the loads are in use. This should give you some idea on how much more alternator you will need, but given your battery is already getting run down, perhaps you do need more.
Edited by devilsadvocate, 19 July 2006 - 09:59 AM.
#7
Dr Terry
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Posted 19 July 2006 - 10:01 AM
Hi Guys.
My point precisely, as I said -
"Either the ammeter is not telling the truth, because it's wired wrongly,"
If accessories are not wired correctly, as devils has said, then the ammeter is not telling the truth.
Dr Terry.
My point precisely, as I said -
"Either the ammeter is not telling the truth, because it's wired wrongly,"
If accessories are not wired correctly, as devils has said, then the ammeter is not telling the truth.
Dr Terry.
#8
Dangerous
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Posted 19 July 2006 - 10:49 AM
DA and I have different opinions on the relative usefulness of ammeters and volt meters, but in your case, I really would suggest scrapping the ammeter and its wiring, rerunning a decent power cable from the alternator to the fusebox, and fitting a volt meter to monitor battery voltage. The reason for this is that the original GTR ammeter wiring is marginal in size when lots of load is on the alternator and/or battery, and being 35 years old by now, I wouldn't be trusting it to cope with the larger loads that you're expecting of it. It also has quite small connectors on both the wiring and the ammeter itself. OK if it's in good nick for a stock GTR or XU-1, but not for a car with lots more electrical load. If you rewire it the way DA and DrT have suggested, it will reduce the current flow through the ammeter and part of its wiring (which is a good thing), but if you have lots of load on the battery, eg running thermos etc when the engine's off, this will still give the ammeter and wiring a hard time.
GTR ammeters have to have all of the current flowing through them to measure it, which is a considerable amount of power. Volt meters on the other hand consume almost no power.
Any VN V8 to at least VS if not VT alternator will be at least 85 amps, and bolt straight in with a small wiring addition, and the V6 ones only need the pulley swapped over with your old one.
GTR ammeters have to have all of the current flowing through them to measure it, which is a considerable amount of power. Volt meters on the other hand consume almost no power.
Any VN V8 to at least VS if not VT alternator will be at least 85 amps, and bolt straight in with a small wiring addition, and the V6 ones only need the pulley swapped over with your old one.
#9
_devilsadvocate_
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Posted 19 July 2006 - 11:13 AM
Nothing wrong with doing what Dangerous has suggested above, I did consider this also: "the reverse load of the accessories in your case through the ammeter when the motor is off or when cranking the starter, but since only a 10amp fan didnt think that would be a prob, but for futureproofness what Dangerous has suggested is good.
#10
Dr Terry
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Posted 19 July 2006 - 11:17 AM
Hi Guys.
Agreed !!
Dr Terry.
Agreed !!
Dr Terry.
#11
_whiteLC_
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Posted 19 July 2006 - 07:46 PM
Of course!!!!!! (and the penny drops).
Thanks guy's.
I DO have the power for the EFI and fuel pumps (via relay) hooked up to the starter (idiot!). Will do some rewiring or maybe go for the volt meter idea, thats sounds good... and safer.
The battery is brand new, so I knew that wasn't the problem.
Some how I was thinking that the ammeter showing full charge was the alternator straining to keep the battery charged (brain fart???) makes sense that it should be other way around.
I have a Hitachi alternator from a 6 cyl VK EFI, pretty sure they are 60 - 70 amp, I'll give that a go (have heard that they're not the best though).
Can anyone help me with the connections on the back.
There is the obvious battery stud.
But there is also a two pin socket plug (any wires that may have been connected have long since gone). I guess one of these gets connected to the +ve battery (as a reference) and one to the alt light.
BUT WHICH ONE IS WHICH, can't see any markings.
Is this correct?? and which one is which??
Cheers
Thanks guy's.
I DO have the power for the EFI and fuel pumps (via relay) hooked up to the starter (idiot!). Will do some rewiring or maybe go for the volt meter idea, thats sounds good... and safer.
The battery is brand new, so I knew that wasn't the problem.
Some how I was thinking that the ammeter showing full charge was the alternator straining to keep the battery charged (brain fart???) makes sense that it should be other way around.
I have a Hitachi alternator from a 6 cyl VK EFI, pretty sure they are 60 - 70 amp, I'll give that a go (have heard that they're not the best though).
Can anyone help me with the connections on the back.
There is the obvious battery stud.
But there is also a two pin socket plug (any wires that may have been connected have long since gone). I guess one of these gets connected to the +ve battery (as a reference) and one to the alt light.
BUT WHICH ONE IS WHICH, can't see any markings.
Is this correct?? and which one is which??
Cheers
#12
_devilsadvocate_
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Posted 19 July 2006 - 09:48 PM
Thanks guy's.
I DO have the power for the EFI and fuel pumps (via relay) hooked up to the starter (idiot!).
Idiot?, think you are being a bit harsh on yourself .........Im sure you weren't robinson crusoe there re the cause of the ammeter readings.
Re the Hitachi alternator: Your guess sounds good, but I dont know for sure!
#13
_Hotrodder_
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Posted 20 July 2006 - 01:24 AM
The VW was widely known to catch fire due to crappy ammeters, and if you keep pushing the GTR one you'll end up with the same severe problem.
As devil and Dr has mentioned, there are good reasons for connectiing the additional accessories off the back of the alternator.
As for the two pin plug on the alternator, they should be labelled with something? maybe just an L?
As devil and Dr has mentioned, there are good reasons for connectiing the additional accessories off the back of the alternator.
As for the two pin plug on the alternator, they should be labelled with something? maybe just an L?
#14
Dangerous
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Posted 20 July 2006 - 11:07 AM
I don't have a very high opinion of the Hitachi units, and I think it's a majority opinion amongst auto electricians as well. I do have a VK service manual somewhere - I'll see if it mentions which alternator connections are which. I don't think the Hitachi alternators have a separate battery reference connection though.I have a Hitachi alternator from a 6 cyl VK EFI, pretty sure they are 60 - 70 amp, I'll give that a go (have heard that they're not the best though).
Can anyone help me with the connections on the back.
Cheers
If you can score a VN onwards Bosch unit, it will be less heartache in the long run than using the Hitachi unit you've already got.
#15
gtrboyy
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Posted 20 July 2006 - 05:29 PM
The hitachi is a 70A alternator,if you already have it & the brackets then use it until it stuffs up,then use the late model v8 unit(vn-vs).
I had a look in the gregory vk manual but it wasn't much help with the wiring so try justcommodores or the streetcommodores sites.
I had a look in the gregory vk manual but it wasn't much help with the wiring so try justcommodores or the streetcommodores sites.
#16
_whiteLC_
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Posted 20 July 2006 - 06:25 PM
Thanks again guys,
Think I'll probably get a VN Bosch one like Dangerous says.
Dangerous:
So is the Commodore Bosch alternator just connected up like gtrboyy said earlier in this post?
Think I'll probably get a VN Bosch one like Dangerous says.
Dangerous:
So is the Commodore Bosch alternator just connected up like gtrboyy said earlier in this post?
And are these alternators marked on the back, in case there are no wires on it?white wire to + of battery
brown wire to alt light
& power wire of alt stud to + of battery or starter motor stud if battery in boot.
#17
gtrboyy
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Posted 20 July 2006 - 07:32 PM
Go to the wreckers & take off a plug with wiring off one of the old vn v6's.Then get your v8 efi alternator,bolt in & enjoy.If your unsure the write or take a pic of where the wires go.
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