This is a mid range petrol engine, diesels, larger/smaller, higher performance, etc. all have a bearing, but it gives you an idea of the profile.
Hi guys,
Hows it going?
Ive been searching for a while but cant really get a definative answer or solution, so thought I would post this!
I really want to have my battery completely fused, Just as my starter motor terminal is quite close to my exhaust. 10mm or so. The starter came off of
a sierra 2.0DOHC and is turning a zetec 1.8. So does anyone have any Idea what sort of current that would draw? Also, Is there any reason not to put
it on the earth side of the battery?
Cheers Jas
Maximum current would be about 30A i would imagine. The starter needs to have the positive supply, as it earths through its chassis.
I'd be surprised if it was less than 100 amps and more likely a lot more especially with a cold engine.
Geoff
Here you go, the spike it getting the engine turning, then it evens out at about 180 amps continuous cranking.
This is a mid range petrol engine, diesels, larger/smaller, higher performance, etc. all have a bearing, but it gives you an idea of the profile.
100A slow-blow fuse on my low compression petrol starter feed.
Cheers for all your replies guys,
Do you think a 250A Maxi fuse on the earth lead would do the trick?
Cheers again, Jas
250A might well be OK but it could get very hot so be careful where you site it!
Geoff.
Do you need a fuse in there? genuine question, my modern cars get main stealer maintained so I don't even lift the bonnet that often, I play with a 67 E Type which certainly doesn't have such a fuse.....
didn't think they were fused on any car?
Fuse for 200a amps in an arctic weather cold start situation the Pinto starter isn't exactly the efficient compared to modern geared units.
In normal starts it will probably only peak at 100 amps for a very short duration.
On older cars this lead was never fused and never caused problems only modern cars have them.
If you do fit a fuse it will have to be fitted in the main feed from the battery to be effective.
Its only because of how close it is to the exhaust that I thought it might be a good plan to fuse it, so if ever the exhaust was knocked, the fuse would blow, instead of the battery (and car) catching fire?
If you fuse the negative you should really fuse the positive too, shouldnt fuse negative alone.
Starter motors take a mahusive amount of electricty to build up the magnetic fields and a slightly smaller amount of power to turn. They're good
on grunt, rubbish on efficiency.
However they are simple and only used for short periods hence no problem.
But if you put a fuse making it a big'un as already mentioned.
Starters on most engines, new or old, put out about 2~3hp, and more.
Do the maths. 2hp~1500watts. =125amps 3hp~190amps
As the graph above shows, startup can spike at up to 4 times turning current.
The above is from personal experience, and measured using accredited equipment, not from i'net or wiki searches!
Put a heatshield between the starter and exhaust with a bit of wrap around the cable . Will cause more problems than it's worth fitting a fuse
having a fuse on the negative side is as good as not having a fuse at all.
Why Ash ?
quote:
Originally posted by ashg
having a fuse on the negative side is as good as not having a fuse at all.
Probably the main reason for fitting a fuse on the positive is safety, putting a fuse on the negative is a bit like shutting the stable door after the horse has bolted
why ? Ash
[Edited on 29/1/11 by alawrence]
quote:
Originally posted by nz_climber
quote:
Originally posted by ashg
having a fuse on the negative side is as good as not having a fuse at all.
This is just plain wrong! I think you will find alot of vehicle DC systems are switched earths, doesn't mean the switch doesn't work.. A fuse is exactly the same.
Although standard practice is to put a fuse as close to the source as possible, in this case it would work fine on the negative. But personally I would put it on the positive side, and also would use a motor rated circuit breaking (means you can reset it if it does trip)
Remember current on the -ve side will be equal to the current on the +ve side of the battery
Putting a fuse on the neg leaves a large part of the curcuit unprotected!
quote:
Originally posted by rusty nuts
Putting a fuse on the neg leaves a large part of the curcuit unprotected!
quote:
Originally posted by rusty nuts
Putting a fuse on the neg leaves a large part of the curcuit unprotected!
Some people obviously don't know thiere arse from thier elbow!
your swimming against the tide here mate ...just let it go
"when in a hole stop digging"
or go to college perhaps...
xx
quote:
Originally posted by Jasongray5
quote:
Originally posted by rusty nuts
Putting a fuse on the neg leaves a large part of the curcuit unprotected!
How? If it breaks the circuit?
if you break the connection to the neg terminal there is no possibility of any current flow...
simples !
i don't care how long you've been working on cars chap you cant deny the laws of physics
quote:
Originally posted by rusty nuts
Some people obviously don't know thiere arse from thier elbow!
quote:
Originally posted by britishtrident
quote:
Originally posted by Jasongray5
quote:
Originally posted by rusty nuts
Putting a fuse on the neg leaves a large part of the curcuit unprotected!
How? If it breaks the circuit?
Fine if only one earth path but from experience long experience this isn't the case on nearly every car I have ever worked. on.
I have seen cars with broken earth braids with the starter current earth current going through the choke cable.
[Edited on 30/1/11 by britishtrident]
electricity will always find earth if given half a chance. common practice on cars is to earth the battery to the body and the engine meaning you
would need two fuses on the negative side. if one of the fuses blew there is a risk that ground would still be found through the other connection
defeating the point of the fuse. obviously if you only have one earth off the battery that is fused you wouldn't have the problem but the large
fuse for the starter would provide no protection for the lower powered devices on the car e.g ecu, relays etc.
at the end of the day the current needed to blow a 250amp fuse is massive, by the time the fuse has blown you would already have plenty of sparks to
set a leaking fuel line on fire.
also if the pvc covering on the negative side rubs away and touches the body of the car it wont blow the fuse but it may bypass it if its after the
fuse which is useless
if you think i am being stupid ask yourself how many production cars have you seen with fuses on the negative side? im yet to recall one.
I suggest this thread is deleted as it contains so much bad and contradictory advice 
Edited to say "potentially dangerously bad"
[Edited on 30/1/11 by ReMan]
quote:
Originally posted by daviep
quote:
Originally posted by rusty nuts
Some people obviously don't know thiere arse from thier elbow!
I'm not sure who this is aimed at as yourself and ash seem to be the only people who are confused as to how this works.
The OP was asking whether a fuse at the negative terminal of the battery would would prevent a fire should the main starter supply cable short circuit on his exhaust.
The answer is yes, any current which flows from the positive also has to flow back to the negative so will blow the fuse and then whatever the cable has shorted against will no longer be connected to negative and no circuit is possible. CORRECT
For a main fuse to protect the wiring from the battery to starter this is fine, for any other circuit which has a lower current limit it would not work fusing the negative side and these should be fused on the positive as close to the positive supply as possible.
ALSO CORRECT(however i don't recall this being brought up)
alawrence - 30/1/11 at 07:24 PMquote:
Originally posted by britishtrident
quote:
Originally posted by Jasongray5
quote:
Originally posted by rusty nuts
Putting a fuse on the neg leaves a large part of the curcuit unprotected!
How? If it breaks the circuit?
Fine if only one earth path but from experience long experience this isn't the case on nearly every car I have ever worked. on.
I have seen cars with broken earth braids with the starter current earth current going through the choke cable.
[Edited on 30/1/11 by britishtrident]
I believe your confusing a poor earth on a device( ie an indicator , starter or wiper motor) and a broken/disconnected connection on the negative terminal on a battery (which is what this thread was originally about)
If you have a poor earth on a device it will often find a path of lowest resistance back to the negative terminal. this is classically demonstrated when training 1st year automotive electricians by increasing the resistance of the return path of an indicator lamp and the result is that the brake lights will also start to flash.
However if you break the connection to the negative terminal you will have no potential difference and therefore no current flow.
Hope thats clear
alawrence - 30/1/11 at 07:37 PMI'm not even going to try and give a detailed response to such mixed up logic except to say that i think that ReMan is correct.
suffice to say that "i refer the honorable gentleman to the answer i gave some moments before...POPPYCOCK"
quote:
Originally posted by ashg
electricity will always find earth if given half a chance. common practice on cars is to earth the battery to the body and the engine meaning you would need two fuses on the negative side. if one of the fuses blew there is a risk that ground would still be found through the other connection defeating the point of the fuse. obviously if you only have one earth off the battery that is fused you wouldn't have the problem but the large fuse for the starter would provide no protection for the lower powered devices on the car e.g ecu, relays etc.
at the end of the day the current needed to blow a 250amp fuse is massive, by the time the fuse has blown you would already have plenty of sparks to set a leaking fuel line on fire.
also if the pvc covering on the negative side rubs away and touches the body of the car it wont blow the fuse but it may bypass it if its after the fuse which is useless
ReMan
if you think i am being stupid ask yourself how many production cars have you seen with fuses on the negative side? im yet to recall one.
alawrence - 30/1/11 at 07:43 PMJason
if this wasn't such a serious topic it would be quite entertaining.
i would suggest you seek advice from an electrical engineer or an auto electrician who will take some responsibility for the advise given
daviep - 30/1/11 at 09:08 PMquote:
Originally posted by ashg
electricity will always find earth if given half a chance. common practice on cars is to earth the battery to the body and the engine meaning you would need two fuses on the negative side. if one of the fuses blew there is a risk that ground would still be found through the other connection defeating the point of the fuse. obviously if you only have one earth off the battery that is fused you wouldn't have the problem but the large fuse for the starter would provide no protection for the lower powered devices on the car e.g ecu, relays etc.
at the end of the day the current needed to blow a 250amp fuse is massive, by the time the fuse has blown you would already have plenty of sparks to set a leaking fuel line on fire.
also if the pvc covering on the negative side rubs away and touches the body of the car it wont blow the fuse but it may bypass it if its after the fuse which is useless
if you think i am being stupid ask yourself how many production cars have you seen with fuses on the negative side? im yet to recall one.
Common practice on cars is to connect the battery to the body and then the engine to the body, giving rise to the phenomenon which BT described. This is not the only way but it is the common way.
I did say that the fuse would have to be the ONLY connnection to the negative.
The large fuse is not protect the starter it's to prevent the wiring glowing like a heater and catching fire, if you have fuel leaks on your vehicles I would suggest repairing them before you go too much farther.
The large fuse is not to protect anything else, anything else should be fused as close to the positive as possible.
The current to blow a 250amp fuse is indeed large, infact it's about 250amps
You are entirely correct that if the insulation rubbed through between the battery and the fuse then the fuse would be useless, however if the same situation occured with a fuse on the positive side then the fuse would still be useless and you would have a dead short and possibly a fire.
I never said that you were being stupid but you did say "having a fuse on the negative side is as good as not having a fuse at all" which is clearly incorrect.
If you feel that any of the advice I've given or points I've made are incorrect please feel free to correct me, every day is a school day
Cheers
Davie
alawrence - 30/1/11 at 09:18 PMI agree
(however with a gun like that if you said BEC were best I would still agree...)
britishtrident - 30/1/11 at 10:07 PMI love "experts" who make sweep statements condemning good sound sensible advice but miss some thing very obvious.
:-)
daviep - 30/1/11 at 10:49 PMquote:
Originally posted by britishtrident
I love "experts" who make sweep statements condemning good sound sensible advice but miss some thing very obvious.
:-)
Please share?
Cheers
Davie
Jasongray5 - 31/1/11 at 01:15 PMMy plan was to earth the engine to the chassis, then have a single earth to the battery, then another fuse with a lower ampage on the positive side of the battery, where it goes to everything else and not the starter, if that makes sence?
Sorry for any confusion
daviep - 31/1/11 at 02:00 PMquote:
Originally posted by Jasongray5
My plan was to earth the engine to the chassis, then have a single earth to the battery, then another fuse with a lower ampage on the positive side of the battery, where it goes to everything else and not the starter, if that makes sence?
Sorry for any confusion
Perfectly acceptable in my opinion.
Regards
Davie