Hi All 

          What's the max amount of 100w spots the 90amp alternator in a vRS will run without causing draining problems ? 

 

There was a formula that I saw many moons ago to calculate this but I can't find it now !! Typical !!

 

Thanks Lads in Advance !

 

 

Each lamp uses about 8.5A so maybe you can figure it out from there.

A 90ahr Alternator will give maximum of 90 amps when the engine speed is above 3000rpm.If the battery is fully charged it will not take any current. So two 100watt spotlights will need 2 x 8.5 =17 amps.So there should not be a problem,BUT if the engine has just been started, battery will take about 50 amps.If other high current items are switched on especially in cold weather, like rear screen heater about 10 amps,heater fan on high say 5 amps,and headlights on full say 10 amps.making a total of about 75 amps will be required.

Once the battery is charged up (about 30 minutes driving) will leave  about 30 amps available which will allow  your 100w spotlights to be used, leaving about 13 amps for other ancillaries like the radio and wipers.  

That does answer it for me lads ! 

 

Great explanation Thanks a mill 😉

Now another question!! 

 

If I put a bigger capacity alternator on let's say go from 90A to 120A will it cause problems with the ECU ? I see it discussed that the feedback from the alternator to ECU is calculated as a percentage of the output  capacity ! 

 

I'm going to have to come clean and fess up ! I am in the middle of a project where I have a lamp pod from a Pug 206 and 4 Hella Rallye 3000 100w light units ! These will draw 35A as quoted above 

 

Now 35A is literally playing with fire and this has to be done right so to supply these I deffo need 120A at least to cover the massive draw 

 

Do different ratings of alternator give different levels of signal to the ECU ? Or is it a case that on a 90A alternator with a 60A draw the ECU sees 2/3 while on a 120A alternator with a 60A draw the ECU sees 1/2 ? 

 

Or has the lockdown given me too much time ? 

13 minutes ago, VanhireBoys said:

is it a case that on a 90A alternator with a 60A draw the ECU sees 2/3 while on a 120A alternator with a 60A draw the ECU sees 1/2 ? 

Exactly that.

No problem will result.

 

I think it only comes into play when the demand is at or near 100%. At that point some 'luxury' current consumers like heated seats or auxiliary PTC electric cabin heaters might be inhibited until the rpm rises (which naturally increases alternator capability) or other demands decrease (e.g. heated rear screen).

 

Edited 21 March, 20215 yr by Wino

Why would you want to run any 100w spots on a vRS?

1 hour ago, delroy said:

Why would you want to run any 100w spots on a vRS?

 

Because he already has the light bar from a pug.

Because rally cars have them.

10 hours ago, sepulchrave said:

 

Because he already has the light bar from a pug.

Because rally cars have them.

Didn't answer my question but each to their own I guess. 

9 hours ago, sepulchrave said:

 

Because he already has the light bar from a pug.

Because rally cars have them.

 

Thanks for clearing that up ! 

A few more reasons I am undertaking this

My commute starts at 4am and it's over really narrow back lanes where there could be livestock broke out of fields and other danger 

 

My car is far from mint and far from original - to do this to a low mileage minter would be a sacrilege 

 

I have been involved with rally car preparation and I was a big fan many years ago and that never leaves you !! John Mulholland a Skoda dealer from Randalstown rallied a vRS in 05 to 07 and showed just how much of a sleeper they really are !!

 

Most of the hardware I already have and the light from these is like hitting an egg with a sledgehammer 

 

Again Wino- Thanks a mill for explaining that - I'd be absolutely lost without this forum's support.

 

I am deffo going to put this project up at some stage as I get it rolling ! 

 

Thanks again lads - now to get the pod sitting right 🤣

 

 

One thing that may be worth considering is upgrading/upsizing the cable between alternator and battery fusebox; that would minimise any resistive losses in that leg.  Not sure if the cars that had 120A alts from new had a bigger cable but I think the standard ones are only 16mm². 

 

For the same reason I would suggest  removing, cleaning and refitting the main earth cable between engine and chassis.  Both ends of this are quite exposed, and the engine end gets thermally cycled too every time the car is used.  Good clean connections on this cable can give you much improved battery charging and general performance of the electrics. Goes to the inside face of the nearside chassis leg and to one of the starter motor fixing bolts at the other end. 

Photo shows the chassis leg end, and the repaired starter solenoid wire just above it.

Edited 22 March, 20215 yr by Wino