One For Vehicle Electrians.

[richard1600]

hi all,,,

need some thoughts,,,

ref: trike re-wire...

have wired a trike a year ago which seemed fine. will try upload some wiring diagrams... but see what you guys think so far.

ok so its a 12v chassis return.... i have a lead from bat+ to isolator switch - then iso sw to starter motor - then to the alternator - then to the ignition barrel. it is fused on the line between alt and ign barrel.

ign barrel then provides outputs at various stages to
1. fuel pump relay
2. starter motor relay
3. main lights switch relay
4. a few minor things such as fuel guage and horn.

so its not highly loaded at all, its just hold on relays etc.. (the main feed for starter motor and fuel pump etc comes direct from isolator switch.)

problem is it all works and has done, but for some reason the fuse on the line between alt and ign barrell now gets hot and blows as if overloaded???

currently a 30amp fuse which will blow once vehicle has been used for 2 hrs or so.. ???

 

[Spark123]

A few relay coils shouldn't pull anywhere near 30A.
How have you connected the supply to the contacts on the relays?
Photos and diagrams will probably help.

 

[richard1600]

from alternator to ignition barrel,,,,, then from the various spade points on the back of the ignition barrell, cables from there to the relay with spade conectors...
the supply to contacts are simply ring conector on the iso switch, along cable then spade to relay.
(all continuities read good)
earths are def not a problem,,,

its all very neat and connected correctly...

am thinking along the lines of the battery for some reason ??? its an old battery,, the alt is charging at around 13.8v at the alt and on the battery..
also it was reported to me that the cables from alt to ign barrell were warm, in particular i noticed it was hot on the fuse conection..
(cable not man enough??? would this cause these conditions??)

all connections are clean and new and all correctly crimped, nothing is loose or coroded etc.

 

[Spark123]

From your description before the alternator is connected pre ignition barrel so this shouldn't be causing the wiring downstream from it to warm up.
All wire has a resistance, when you pass current through it a small amount power is lost which is where the heat is generated from. The larger the cable, the lower the power loss for a given current. Cables can get warm in use but it shouldn't be getting hot.
What size is the cable?
Can you post up some photos and a wiring diagram?

 

[richard1600]

am working on pics now,,,, vehicle is at a clients so cant go out there but am working on trying to get my diagrams online...

as for cable,,,, alt to ign barrell is rated at 35amps,,, on initial calculations this was more than enough but clearly its close to the limit hence adding to problem,,,..

the cable is warm but the fuse gets hot,, perhaps the insulation is damping the heat on my finger from the cable??

 

[richard1600]

Untitled

• richard1600
• 19 Sep 2010
• 1

 

[richard1600]

guys, sorry for poor pic,, but this is the basic cct...

ign barrel is to hold-on contacts on relay,,,, the main power through the top of the relays ie:to the componets comes from Iso (isolator switch)..

obviously everything is earthed appropriately,,,, and there are a few extra things off ign barrel,

the guages, horn, small indictaor dash lights, the small lights for 4 guages and i think the brake switch...

thx guys

 

[Spark123]

A couple of normal relays shouldn't be drawing anywhere near 30A. Are you absoultely sure they are wired correctly? How big are they and what is the resistance across the relay coils?
The starter motor solenoid will take a few amps but is only a momentary action.

 

[BenBag]

The more conventional setup would have the main fuse as close to the battery as possible (in your case, after the starter motor) and (perhaps more importantly, see below) to run the output from the altenator directly to the battery +ve.

Also, you say the main feed for the fuel pump etc comes from the isolator, it which case, all of that wiring seems to be unfused (unless they are seperately fused??)

Having said that, I can't see why the 30A fuse should blow, you'd still need a sufficiently large current draw, which you don't seem to have. In your boots I'd disconnect the alternator and run the whole thing off the battery for a while, see if it still breaks.

What I suspect is happening to you is that everything you have there which is powered via the ignition switch is running of the unsmoothed output of the altenator - i.e. it's very noisy/spikey - The altenator will be relying on the battery to act like a giant smoothing capacitor. You could be getting pretty big voltage spikes on there (especially when you start or stop the engine) which are overloading the fuse.

b.

 

[TicklyT]

Where is the power feeding the auxilliaries controlled by the relays actually supplied from?

 

[Mursal]

Would it be possible that you have one of the relays getting power through
the fuse instead of from the battery circuit. Disconnect pin 30 on each relay
in turn and wait to see if the fuse blows. Pin 30 should be getting power directly from the battery side of the starter solenoid. Eventually you should get one that when disconnected the fuse wont blow, and you have found your problem circuit.
If the fuse keeps blowing with pin 30 disconnected from all the relays, there is a short in one of the relay coil circuits.
When you get your problem sorted you may want to put additional fuses on the supply to pin 30 of each relay as the single fuse you have at the moment wont protect all the wiring.