Thread: Alternator voltage drifts down as I drive

Hi, the voltage drop after some driving is normal but the voltage should not drop below 13.5(at the alternator output)... depends from where did you pick up the voltage reading cos if it's from the fusebox, ECM or other circuit i'd say it's ok and your problem with the throttle is not related.

The alternator is meant to do that. It is a good alternator. It means the alternator does not over charge the battery, therefore the battery should last longer.

I'd hazard a guess to the issues are not related. Perhaps you have a faulty throttle potentiometer. There is an easy way to check if you have a Nanocom. Use the google search at the bottom left hand side of any forum page to find out how.

See my last post in another thread about this ... new gen' Denso to replace the original (180,000km/11years) and voltages are well above 14v (like they used to be and were for years) ...

... then FWIW I'm browsing the current ARB April 2015 price list, not long after reading the OP opening post, and in the dual battery section of the price list I read ...

"DUAL BATTERY SYSTEM - SERIES 2
1,2,3(4332130) Non-Rear Air Con Models, Max 16kg Weight Capacity ...

... and the "1" is listed below the entry as ...

"1This vehicle utilises a temperature sensing alternator system. The Standard ARB Dual Battery System is equipped with the Redarc SBI12 Controller which under certain conditions will not allow the auxilliary battery to be 100% charged. For those conditions ARB recommend an upgrade to the Redarc BCDC. Please consult with your local ARB outlet for more information.

WHAT!!?? ... that's news to me, and possibly the rest of you !!

The D2 uses a temperature sensing alternator ?? ... the spec' for the genuine Denso alternator (that I found online) makes no mention of "temperature sensing" ... and if it's so, why did MY alternator not "sense" the temperature and reduce the charging voltage for the 4years prior to the problem developing ??

... confused ??? .... Ooo Oooo ... that's right, I need a DC-DC charger !!

I'm also confused! The original alternator which came with the vehicle 9 years ago always maintained the voltage at 14.2v. Since it packed up some years ago, I have fitted genuine Denso units. I think that I have 2 old units in the shed, time for a look to see what they are. One of them is probably not a Denso.

Today I drove from Springsure to Bedford Weir near Blackwater - about 170km. By the time I reached the weir, voltages were down to 13.4v after starting this morning at 14.2v. With the engine stopped for a while, the main battery is now at 12.2v & the second battery is at 12.4v but the fridge is attached & running.

Something is not adding up! Checked all the earth headers I could find yesterday. Do I dare to connect my caravan with 2x120aH batteries to my Disco? Maybe the solar panels will charge the Disco's batteries if I do.

Thanks Jazzman. I need to remember to connect the Nanocom while driving to see if I can catch what is happening. Seems I could also have a faulty IAT/MAP sensor also (according to Rave)

yes,, your panels will charge the starting batt

My alternator also has a large voltage drop as the engine warms up. Gets as low as 13.0 V with aircon and head lights on (measured at battery).
Has anybody considered, or successfully put a repair kit through their alternator?
I found a repair kit,
Alternator Repair Kit Land Rover Discovery Discovery II 2 4 0L 4 6L V8 1999 2004 | eBay


And even came across some instructions.
How-to: Disco II Alternator Disassembly - Land Rover Forums - Land Rover Enthusiast Forum

Originally Posted by Milton477

I'm also confused! The original alternator which came with the vehicle 9 years ago always maintained the voltage at 14.2v. Since it packed up some years ago, I have fitted genuine Denso units. I think that I have 2 old units in the shed, time for a look to see what they are. One of them is probably not a Denso.

Today I drove from Springsure to Bedford Weir near Blackwater - about 170km. By the time I reached the weir, voltages were down to 13.4v after starting this morning at 14.2v. With the engine stopped for a while, the main battery is now at 12.2v & the second battery is at 12.4v but the fridge is attached & running.

Something is not adding up! Checked all the earth headers I could find yesterday. Do I dare to connect my caravan with 2x120aH batteries to my Disco? Maybe the solar panels will charge the Disco's batteries if I do.

Thanks Jazzman. I need to remember to connect the Nanocom while driving to see if I can catch what is happening. Seems I could also have a faulty IAT/MAP sensor also (according to Rave)

No problem. The two voltages 12.2 and 12.4, were they measured with the batteries coupled together? If so the readings are not accurate as the batteries are in parallel so they should measure the same, with maybe some voltage drop in the cable. The voltages you have read are so close that it could be exactly this. Disconnect one battery and measure the voltages again to get an accurate reading of the individual battery voltage if you believe you have an issue.

Could also be a failing battery. A bad cell will have an inhibiting effect on correct charge rate and dont dismiss the idea if the battery is near new.
Cheers Scott