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Idling, driving slowly for 2 hours


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I took my Caterham when I sent to get vaccinated the other day. I didn't expect a long, slow moving line. We were in stop and go (mostly stop) traffic for 2 hours. Then the car had enough and stalled out. A quick checks showed that my battery was below 9 volts.

 

I have a lithium ion battery. When I got the car home, I charged it over night to about 13.5 volts. The charge drifted down to 13.0 volts after 3 days, which is normal. It usually drops to the high 12s after a few days and will hold the mid 12s for months. I took it out for a 6 mile drive near the house this morning and the voltage on the battery increased slightly from the 13.0 initial voltage to 13.5 volts. During the drive, the voltage showed between 12.8 and 14.0 volts.

 

Am I wrong in concluding that things are working fine and that the problem was that my alternator doesn't put out enough amps at idle to sustain the car for hours, especially when having to run the radiator fan? Or am I missing something. I thought my next trip would be in the 20-30 mile to give it another test.

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Could try disconnecting the battery after starting the engine then switch on lights etc to load it up, see what happens at idle and higher rpm? Sure sounds like an alternator issue of some kind.

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There is a simple test, use a volt meter and measure your battery voltage with the car not running. Start the car let it warm up and settle to a steady idle, measure the battery village again with the engine running. If voltage running is less than voltage not running your alternator is not putting out enough current at issue speed. My tiny alternator has that problem, but I don't spend extended time at idle.

 

Graham

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Caterham’s rarely put out enough voltage at idle to charge the battery.

 

Please explain as I would expect the alternator's voltage regulator to maintain ~14v output when the engine is running??

 

{I'm not an engineer}

p.

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Please explain as I would expect the alternator's voltage regulator to maintain ~14v output when the engine is running??

 

{I'm not an engineer}

p.

 

The voltage regulator cannot output a higher voltage than it gets from the alternator.

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The voltage should be around 14v even at idle. Sounds like you've got an alternator issue. The voltage regulators are internal so you there's not much you can do there. 

Take it out and get it tested. Hopefully you have a good old fashioned starter/alternator repair shop in your area that give it good look see.

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I have a 40a alternator on my Birkin. Several years ago, I ran into a similar problem where due to a heat wave in SoCal, coincident with my driving to an event on surface streets in LA. My car uses an electric coolant pump as well as both low and high pressure fuel pumps. As usual, I managed to hit nearly every red light as it started to get dark. With the lights on, they would go dim at idle with all of the other electrical load. Voltage was dropping to 12 or so (without accurate testing, we only presume that a new VDO gauge is accurate). In order to keep the coolant temp reasonable, I had to resort to manually idling at 1500 rpm as well as killing the lights when stopped at a light. All in all a bit nerve wracking. Afterward, the alternator tested perfect on the bench. I eventually changed all of the lighting to LED, revised the programmed settings for the coolant computer and raised the idle to 1000 rpm. I also avoid long trips across town in hot weather at night. Haven’t had a problem since. Correctly engineer the electrical loads to the extent possible. Have an auto electrical shop bench test both the alternator and volt meter. You may want to change the size of the pulley and adjust the idle for an event like that. Good luck.

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