Alternator voltage at tickover

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Alkers
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Alternator voltage at tickover

Post by Alkers » Thu Oct 03, 2019 2:49 pm

What voltage should I be seeing on the batteries from the alternator when the van is idling?

I'm getting up over 14V when the engine is reving but at idle it can be below 13. I have been having starting & cutting out issues so a lot of cranking lately. Batteries on charge now today.
Flanners
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Re: Alternator voltage at tickover

Post by Flanners » Thu Oct 03, 2019 3:04 pm

I would say that is too low, you should be on about 14 (mine fluctuates between 14.2 and 14.6). Alternator on it's way out?

Test the battery as well as that too could be knackered/on it's last legs.
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g8dhe
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Re: Alternator voltage at tickover

Post by g8dhe » Thu Oct 03, 2019 5:05 pm

Actually 13.5 ish wouldn't be too low when idling, the resting voltage of the battery is 12.6-12.8 volts when no current being drawn or charged, 13.6-13.7 is the normal float charge level which is when the battery is at a total balance, that is to say any internal losses and being cancelled out and a battery can sit at that voltage happily for many months on end provided it is in a fully charged state, to actually put more charge in then voltages up to 14.4 is fine, above 14.5 volts gassing starts which is where Hydrogen and Oxygen are being broken down and electrolyte is being loss so to be avoided!

The normal charging regime for a flooded lead acid (NOT GEL, VRLA or AGM) for say a 100AmpHr battery (Capacity - C)
is Initial charge replacement is a constant charge current of between 5 amps(gentle C/20) - 20 Amps(aggressive C/5) until the battery voltage reaches 14.4 Volts - this will refill the battery to around 70-80% of its full capacity (C).
Then 14.4 volts is maintained until the current is down to about 3-5% of C i.e. 3 to 5 Amps for a 100AmpHr battery this is often called the Topping charge.
A third stage not always needed and needs to be carried out with care is to level or balance the individual cells in the pack, which is normally around 14.6 Volts for 2-3 hours, however this isn't needed every time at all just once or twice a year would be fine.
Finally once fully charged the charging voltage is dropped to 13.6 volts and this can be maintained indefinitely.

An alternator will normally only carry out the 1st and 2nd stages and will then continue charging at the 14.4 voltage, however its not often that journeys would go on for sufficient time for this to occur and cause trouble, breaks and refuelling will ensure that you need to restart the engine and draw some energy from the battery!

If you want to read the full story then https://batteryuniversity.com/learn/art ... id_battery is the place to delve!
Geoff
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Alkers
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Re: Alternator voltage at tickover

Post by Alkers » Thu Oct 03, 2019 5:12 pm

Alternator is a replacement from a scrapyard so no idea as to it's history but the old one failed and was binned and this was only €40.
If it's not charging at idle but does so fine when revving, is there an adjustment that can be made or is it likely on the way out?
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Re: Alternator voltage at tickover

Post by g8dhe » Thu Oct 03, 2019 5:57 pm

Not aware of an adjustment, the internal regulator chip controls it all, provided you get several amps charging at say 1200 rpm and a full 14.4 at higher revs then I would think you will be OK.
Geoff
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