Battery/main loom fuses

[85Fuego]

Would like some advice from people in the know.

Have relocated battery to the back.
Will fuse the main supply cable.
On cold start, draws 70 Amps.

What do the experts recommend:
Fast or slow blow?
150% or 200% of starting current.

Am thinking of using something like this mounted to the pos terminal.

Thoughts????

 

[Roland]

Whats the actual time difference involved between a fast and slow blow fuse?

I understood it was a matter of seconds.

In which case, does it really matter?

I doubt a slow blow fuse will allow more time to activate the starter motor - the biggest drain on the battery.

No doubt there are people on the forum who will be able to do some calculations for you.

I am certainly interested as I will be moving the battery in my V6 406 to the rear to allow space for a turbo and a decent fuse in the system as well as an emergency cut off switch is a good idea!

Cheers
Roland

:banana:

 

[jaahn]

Hi
Remember main fuse is to protect the wiring, so should reflect the max current capacity of the wire.
Does your 70A include the starter ?? Does not seem enough for that. But too much for everthing else.
Alternator output ?
Jaahn

 

[85Fuego]

Hi
Remember main fuse is to protect the wiring, so should reflect the max current capacity of the wire.
Does your 70A include the starter ?? Does not seem enough for that. But too much for everthing else.
Alternator output ?
Jaahn

Hi Jaahn

New wire is 50mm2 (15mm diam) which is enough to carry bucket loads of current.
Had no idea of current draw so got a "just in case size".
I see that cable is rated min 200A.
I figured that the most current draw is at startup (70A).
Hence the safety factor of 150/200%.
Everything else would be protected by the factory rated and installed fuses.

Roland

Main fear is short to ground if there was a problem.
The curves below tell me for the 150A fuse curve a dead short (600A) would blow in 0.11 sec.
The rated current 150A would blow in 2000 sec (33mins) a bit too slow for my liking.
Hence the fast slow blow question.

 

[REN TIN TIN]

You sure it's 70 amps?
The recommended battery for the Fuego would be rated at what, about 350CCA - 400CCA (Okay CCA is at minus 18 degrees so it even higher when warm). You wouldn't need a 350 amp battery if your starter is pulling 70 amps max.
Is the 70 amps the specification in your Renault manual or Haynes or an estimate?

 

[mistareno]

I used a circuit breaker like this on mine.

It also allows you to isolate the car by pushing the button.

 

[robmac]

Main fear is short to ground if there was a problem.
The curves below tell me for the 150A fuse curve a dead short (600A) would blow in 0.11 sec.
The rated current 150A would blow in 2000 sec (33mins) a bit too slow for my liking.
Hence the fast slow blow question.

If the short were at the battery terminals I 100% agree.

However, if the short were at the starter end, or an intermediate point of the cable who knows the current ?

Respectfully, I would not bother with a main battery CB or fuse. Most oem wired cars don't have them. And I'd suggest the money is better spent on double insulating the , longer, starter lead and locating it place where the risk of damage is minimised.

The only addition I 'd suggest, if it's not already there, is to fuse the alternator main charging lead.

 

[Roland]

85Fuego,

I'd love to see a picture or two of the battery installation!

Did you just bolt it in the boot of fit a fully enclosed and vented battery box?

I have to go down this path with my 406 V6 turbo project car a bit later this year so all information and ideas gratefully noted!

Cheers
Roland

:banana:

 

[85Fuego]

fusing/breaker options

I used a circuit breaker like this on mine.
It also allows you to isolate the car by pushing the button.

mistareno - will look into that as well.

If the short were at the battery terminals I 100% agree.
However, if the short were at the starter end, or an intermediate point of the cable who knows the current ?

If there is a short along the main cable, with such a large cross-sectional area, my thoughts are it would draw such a large current irrespective of where the short is.

Respectfully, I would not bother with a main battery CB or fuse. Most oem wired cars don't have them. And I'd suggest the money is better spent on double insulating the , longer, starter lead and locating it place where the risk of damage is minimised.

In this case the cable goes straight from the pos terminal of the battery to the starter.
The cable has 2 insulating layers, I have added heat shrink along the entire length with grommets where protrusions have been made with cable ties to minimise movement.

You sure it's 70 amps?
The recommended battery for the Fuego would be rated at what, about 350CCA - 400CCA (Okay CCA is at minus 18 degrees so it even higher when warm). You wouldn't need a 350 amp battery if your starter is pulling 70 amps max.
Is the 70 amps the specification in your Renault manual or Haynes or an estimate?

Hi Ren,

The current was recorded using a dc clamp-meter with peak hold.
Ran the car radio full pelt with the fan up to max and it drew 7.8A.
So with the radio, fan, windows, other circuitry running, 100A is not beyond belief.
Thus my ball park figure of 50% safety factor and 150A fuse.

As a comparison the Koleos (diesel) on a cold start drew 402A on a 7C Melbourne morning.

I'd love to see a picture or two of the battery installation!
Did you just bolt it in the boot of fit a fully enclosed and vented battery box?
I have to go down this path with my 406 V6 turbo project car a bit later this year so all information and ideas gratefully noted!

Roland

Will provide - will share the knowledge.
Always good to see what other people have done, gotten away with.

 

[REN TIN TIN]

Hi Ren,

The current was recorded using a dc clamp-meter with peak hold.
Ran the car radio full pelt with the fan up to max and it drew 7.8A.
So with the radio, fan, windows, other circuitry running, 100A is not beyond belief.
Thus my ball park figure of 50% safety factor and 150A fuse.

As a comparison the Koleos (diesel) on a cold start drew 402A on a 7C Melbourne morning.

Hello 85Fuego,

Unless you've got all the accessories running while you're cranking the engine it doesn't matter how much current they draw.
The battery is only required to crank/start the motor.
Once the engine is running the alternator would (or should) supply all the power necessary to run the motor and all ancillaries and to recharge the battery. Back in the days of the generators, the battery might have been called upon to supply some power while the car was idling but not with an alternator. If you've got a fault with the alternator you might be pulling some power from the battery but an alternator that's not faulty and of sufficient rating should power everything with the motor running. (We've all jump started a car with a dead battery at some stage and once they running they're okay even if the battery is still dead).

400 amps to start a diesel Koleos sounds about right. Obviously a petrol engine has much lower compression than a diesel so would draw less current but a 2 litre petrol motor would likely be over 100 amps. As mentioned previously, the recommended minimum battery capacity for a Fuego is about 300CCA - 350CCA. Even with a 50% safety margin, you'd be in the range of 150amps - 175amps.

Personally, I'm not a fan of current Clamp Meters. Love them for AC current not not for DC current. Unless you've got a pretty good model, the readings aren't accurate. That's if the meter can actually measure DC current at all, a lot of them are AC current only and can't measure DC current. Not saying your readings are wrong and there's anything wrong with your meter or method, but putting in bigger wires/fuses now is better and cheaper that replacing them later.

If you're going for say, 150 amp cable, give it a test and try to jump-start the Fuego with the cable. (If you have a convenient dead battery, put it in the Fuego for the test so all the current is coming from the 2nd vehicle through the cables). You're going to need about 2 - 3 metres of cable to go from the boot to the engine bay so it will be long enough to use as a jumper lead. If the Fuego turns over okay with the cable then use it. If it struggles, use something bigger.

Cheers
Ren

 

[85Fuego]

Unless you've got all the accessories running while you're cranking the engine it doesn't matter how much current they draw.
The battery is only required to crank/start the motor...

Ren,

Agreed, that's why I mentioned that there is a possibility that the high current draw items might be on as well (didn't include windows) whilst at startup, and included them in the initial case scenario.

Personally, I'm not a fan of current Clamp Meters. Love them for AC current not not for DC current. Unless you've got a pretty good model, the readings aren't accurate. That's if the meter can actually measure DC current at all, a lot of them are AC current only and can't measure DC current. Not saying your readings are wrong and there's anything wrong with your meter or method, but putting in bigger wires/fuses now is better and cheaper that replacing them later.

The readings were done with a dc capable model.
Who has a meter that will read 100A?
Didn't want to stuff around with a shunt.
Even if the readings are out by a considerable margin, (doubt it would be an order of magnitude), it highlights the difference between what is being drawn and what is capable of supply.
The bigger is better method of modifying is being done at the moment, so the replacement is avoided.

As mentioned previously, the recommended minimum battery capacity for a Fuego is about 300CCA - 350CCA. Even with a 50% safety margin, you'd be in the range of 150amps - 175amps.

Usually I purchase a battery on Ah and RC (reserve capacity).
In this case the driving force is:
a) weight relocation
b) current capacity (adequate)
c) protection
d) acceptance that the RC is reduced

The battery that was installed was 65Ah 600CCA RC120.
The replacement is 40Ah 500CCA RC70.

More than enough to start, however, adequate for track days.
And, and.......sealed, so can be mounted on its side out the back.

Don't get me wrong, I am taking everything on board that people are saying, and applying that to my situation.

 

[jaahn]

Fuses at the battery VW Caravelle !

Hi 85Fuego
I have wrecked two VW Caravelle/Transporters, 1998/1996. They have big fuses at the battery as well as LOTS and LOTS and LOTS of smaller fuses EVERYWHERE else. I have these bits in the shed. If you would like the one shown you could have it for postage !!

However to your question. The 1998 Caravelle, which has can bus system etc, has the whole system fused at the battery, with the starter cable 175A, then 50,50,50,40A, all flat link fuses and a couple of smaller plug-in fuses. I do think the first 50A goes to the main secondary fuse box and the next two go to the big thermo fans close by. Dual a/c in this one !
Jaahn

 

[REN TIN TIN]

The Europeans like to use the AH ratings when talking about battery capacity but while this is fine for standby batteries and the like, for a starting battery the CCA is more important. For starting you need very high current for very short periods where the standby need to supply low(er) current for long periods. For starting you might have to provide say, 200amps for 5 seconds or less if your motor is okay (this includes thing like fuel pumps, heater fans, stereo, etc. that usually aren't turned off while starting).
In very cold weather or if there is a problem with the motor (e.g. timing out, fuel delivery, etc.) you might have to crank a bit longer or if your motor is really out of tune could be a few minutes, off and on. Standby and starting batteries are constructed differently.

Yes, there is a direct correlation between CCA and AH but try starting your car with a standby battery and you're likely to be unable to start. Reserve capacity is not relevant for starting, this is just a measure of how long a battery can deliver 25amps. Obviously 25 amps is not enough to start a Fuego or much else bigger than a small motorbike on ride-on mower. If you're going to sit in the car with the motor not running and using power (e.g. camping) than you might be interested in the RC but it makes no difference to starting and starting is where the battery is called upon to supply the largest current.

The battery you've been using (600CCA) is more than adequate for the Fuego.
You could probably go even smaller if space is now an issue with the battery in the boot.

 

[85Fuego]

Finished - battery now relocated

Have now relocated battery, added new main fuse.
Had to run cable up RHS of car to avoid boot loom on LHS.

Fuse as employed

Fuse attached to battery (now main fuse 150A)

Fuse to isolating switch

Entering sill - double heat shrunk

Exiting sill

Across

Entering engine bay

Exiting to engine bay

A 12V hot point - accessable

Covered

 

[robmac]

I have to say, I couldn't have done better myself.

And that would have to be a first.

 

[COL]

Have now relocated battery, added new main fuse.
Had to run cable up RHS of car to avoid boot loom on LHS.
View attachment 100914
Fuse as employed
View attachment 100917
Fuse attached to battery (now main fuse 150A)
View attachment 100911
Fuse to isolating switch
View attachment 100912
Entering sill - double heat shrunk
View attachment 100918
Exiting sill
View attachment 100919
Across
View attachment 100920
Entering engine bay
View attachment 100913
Exiting to engine bay
View attachment 100915
A 12V hot point - accessable
View attachment 100916
Covered

Looks good to me, a nice professional looking job, well done