Alternator Output

[WIL35]

If my alternator is putting out 12.4V at idle (measured at the terminal on the alternator), does that mean it needs replacing?

My battery light has started glowing ,doesn't seem to matter what the revs are, even glows at 3k revs on the motorway. I checked the voltage at the battery too, it's the same 12.4V, so cabling and big fuse must be ok.

It seems to spin over fine on the starter, so there aren't obvious symptoms. Although it seems to be a bit 'shunty' when driving at a steady speed, that could be 40 or 70mph.

Thanks

[CerbWill]

Get RSAJP connected and logging whilst on a run. Due to pulley sizes the alternator often isnt spinning fast enough to charge the battery at idle. The charge light can come on because the regulator pack is failing and providing too high a voltage with the engine at speed, as happened to me (15.6+V).

[RUSSELLM]

With a few revs, you’ll need a minimum of 13.2v at the battery, to charge it.

Providing you’re testing using a good earth. And there’s good continuity from the alternator terminal to the battery, then the alternator is looking like your culprit.

[ChimpOnGas]

You should be making 14v, but before condemning your alternator check your battery terminals are secure and the earth cable is secure to your chassis.

[Byker28i]

And the big fuse?

[Jimm218]

A friend had this the other week on his. We changed the main power cables (starter, big fuse, battery) and the main battery earth and that sorted it out. On inspection the cables were all looking corroded.

[Penelope Stopit]

WIL35 said:

If my alternator is putting out 12.4V at idle (measured at the terminal on the alternator), does that mean it needs replacing?

My battery light has started glowing ,doesn't seem to matter what the revs are, even glows at 3k revs on the motorway. I checked the voltage at the battery too, it's the same 12.4V, so cabling and big fuse must be ok.

It seems to spin over fine on the starter, so there aren't obvious symptoms. Although it seems to be a bit 'shunty' when driving at a steady speed, that could be 40 or 70mph.

Thanks

A glowing warning light points to blown alternator diodes, burnt stator windings or volt-drops

[WIL35]

Thanks all.

I think I'll check the cables and clean up all the connections first. If it is still glowing I'll fit a new alternator. Something to look forward to.

I gather it is either fuel rail off (with or without throttle bodies) or move the air con pump out of the way and move it through the front of the engine.

[ukkid35]

WIL35 said:

I gather it is either fuel rail off (with or without throttle bodies) or move the air con pump out of the way and move it through the front of the engine.

You may struggle to fit the belt if you don't have access from above

[Wolvesboy]

Sorry to hijack the thread but my battery light has started glowing also!
Very feint on idle, increases brightness with revs.
12.7 at idle
13.78 at 2k revs
Changed big fuse
Wires look ok
Drove for 20 mins to see if voltage drop etc - exactly the same??

[ChimpOnGas]

Do check those battery terminals and cable connections.

[url|https://thumbsnap.com/xfqIZSCg[/url]

The poor connection at my above positive terminal was a function of three elements:

1. The missing screw

2. The fact when I removed the screw it was clear it was the only solid contact point

3. With the one remaining screw removed the cable literally slid out of the terminal like a dick in a shirt sleeve

And worse still heres how I found my negative terminal:





You also must very carefully inspect your main charge cable and earth cable as these are both subject to internal corrosion and so high resistance.

[phillpot]

ChimpOnGas said:

2. The fact when I removed the screw it was clear it was the only solid contact point

If the screws, or screw in your case, are tight the main contact point is surely the "other side" of the cable against the bottom of the hole through the clamp?

Either way, rubbish clamps get something better

[WIL35]

CerbWill said:

Get RSAJP connected and logging whilst on a run. Due to pulley sizes the alternator often isnt spinning fast enough to charge the battery at idle. The charge light can come on because the regulator pack is failing and providing too high a voltage with the engine at speed, as happened to me (15.6+V).

I connected RSAJP yesterday. It started off showing some quite high voltages (15V+) then settled down to around 12V. I checked this independently with a meter on the terminal on the back of the alternator (to eliminate cable problems) and got the same result. It didn't seem to change with higher revs either.

Will order a new alternator on Monday...….

[WIL35]

Thanks for all the responses.

To wrap this query up; I fitted a new alternator (swapped pulley etc) by putting the a/c unit to one side and maneuvering through the front of the engine. The most useful tools doing it that way were some very long nose pliers and one of those flexible claw pick up tools.

This seems to have cured the problems, no beeps from the ECU/MIL, it runs much smoother, doesn't stall and is able to go at steady speeds without 'shunting'. Very pleased and as Ed China would say 'a job well done'!

[Penelope Stopit]

I wonder if your new alternator is driven by a 14.5 volts regulator rather than a 14 volts , they make a big difference yet people here at the TVR forums don't seem to be aware of them

[WIL35]

I got the new alternator from TVR Parts, so I assume/hope it is the right specification

[Byker28i]

When I got my car back from the engine refit, one of the issues was a lot of electrical issues, poor charging, indicators/hazards randomly went, tacho random, which turned out to be the engine earth strap was broken down to just a couple of strands remaining. Under £30 to refit all new cables

[Penelope Stopit]

WIL35 said:

I got the new alternator from TVR Parts, so I assume/hope it is the right specification

The thing is, both 14 volt and 14.5 volt regulators are the right specification

[ChimpOnGas]

phillpot said:

If the screws, or screw in your case, are tight the main contact point is surely the "other side" of the cable against the bottom of the hole through the clamp?

Either way, rubbish clamps get something better

No no no no no

I believe in doing the job properly so I won't entertain the above bolt up type terminals and was glad to get rid on my screw type too, a proper crimping is the only solution.

At my battery I now have two stout ground cables and the one live charge/starter cable all in far thicker 50mm² gauge high quality marine tinned cable, these are correctly crimped with my hydraulic crimping tool that applies 13 tonnes of crimping pressure to the proper tube type tinned copper ring terminals terminals!



Here's how these tube type ring terminals look at the connection end directly compared with the small gauge cable efforts from TVR that weren't even correctly finished and protected against corrosion with glue lined heat shrink as they should have been.





My properly crimped and glue lined heat shrunk insulated ring terminals are securely bolted to my new 'Two Up' forged brass battery terminals so every cable is now a proper ring terminal to stud arrangement which is a far more secure connection, the forged brass Unilug 'Two Up' terminals themselves being in a different league of quality than anything you can buy in the UK these terminals are engineered in Australia for the four wheel drive expedition market.

[url]|https://thumbsnap.com/53eRsigM[/url

The excellent 'Two Up' battery terminals from Unilug give you plenty of connection flexibility, seen here in the stud configuration I use and also the post arrangement should you choose to go that way.



These terminals really are in a different league, they are forged brass not cast and clamp tightly and directly to my Odyssey PC1500 which itself uses proper tinned brass terminals and is a battery of the very highest quality to match the lovely 'Two Up' terminals I'm now using.

[FarmyardPants]

Wow, battery terminal porn