Sanzomat
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| posted on 13/9/22 at 07:00 PM |
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Is 14.8v too much?
Hi all, I'm trying to work out why my battery seems to have died prematurely. Locost with a R1 4XV motorcycle engine. New motorcycle battery (AGM
type) fitted around 2 years ago. The car is only used for track days, about 4 per year. Up until now the battery has held its charge well. I usually
put it on a smart charger every couple of months but it normally only takes an hour to say its fully charged and go into test/maintain mode and it
passed the drain tests.
Last track day was 9th August and it seemed to be fine, no problem cranking/starting.
I did a track day today. When I checked the car over yesterday the battery had become too flat to crank it over. No obvious sources of drain that
would have flattened it over the last month. I charged it overnight and by this morning the smart charger seemed happy and the charge rate had dropped
to its lowest trickle setting. The engine cranked okay but wouldn't start. I put jump leads across from the tow car and it started up fine but
all day it won't start from the battery but starts fine from the jump leads.
I have an acumen gear indicator with voltmeter so can see the voltage whenever the ignition is on. The battery reads around 13.2v with ignition on,
engine off. While cranking it drops to 10v and won't start even though cranking fairly quickly. I'm guessing the 10v isn't enough to
run the ECU/ignition coils hence not starting. While cranking off the jump leads the voltage doesn't drop under 13v and fires up pretty much
instantly (once the unburnt fuel from the failed attempts at starting off the battery have gone)
With the jump leads attached and tow car engine running (locost engine not running) the voltage reads 14.2v which seems to be the tow cars regulator
voltage. With the locost engine running fast idle the voltage shows 14.8v and stays there whatever you rev it to so seems the yamaha regulator is set
to 14.8v.
I've read some stuff that says AGM batteries shouldn't be charged above 14.8 but that suggests 14.8 is okay.
The Yamaha service manual says the regulator is duff if it reads above 14.8 but again that suggest 14.8 is okay.
So, it seems the battery has prematurely aged. I'm wondering if the 14.8 is the culprit here. If 14.8 is the limit for the battery and the
highest the regulator should go to then is 14.8 actually bad? Or, is 14.8 okay and I've just been unlucky with this battery?
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Dingz
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| posted on 13/9/22 at 09:46 PM |
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Had a similar problem recently but on a boat with leisure batteries. Seems like the batteries were failing and charge voltage went up to compensate.
Changed the batteries and voltage dropped back to normal.
Phoned the local ramblers club today, but the bloke who answered just
went on and on.
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coyoteboy
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| posted on 14/9/22 at 08:40 AM |
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My understanding is that 14.7 is the max you want to reach on any lead acid battery. Maybe if you were running he OEM yam battery they'd be
better able to cope with the extreme.
That said, I've had batteries die prematurely in perfectly normal working daily drivers.
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chillis
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| posted on 14/9/22 at 09:25 AM |
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Where is the battery located, does it get hot? Heat kills batteries more than voltage though too much voltage can itself cause the battery to get
hot.
14.8v is the top end but it shouldn't have killed the battery. Are there any spec's for the battery? Manufacturer may have some values that
should not be exceeded?
Never under estimate the ingenuity of an idiot!
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Sanzomat
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| posted on 14/9/22 at 10:23 AM |
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quote:
Originally posted by chillis
Where is the battery located, does it get hot? Heat kills batteries more than voltage though too much voltage can itself cause the battery to get hot.
The battery is under the bonnet on the scuttle. A reasonable distance from the engine but I guess some heat soak would occur. No worse than most
normal cars though as most batteries are under the bonnet. However, the previous track day in August the ambient was mid thirties and whilst the car
wasn't overheating the driver certainly was! Even the GoPro was getting too hot and turning itself off so maybe that was what upset the battery
and would explain why it was almost flat 4 weeks later.
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coyoteboy
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| posted on 15/9/22 at 12:14 PM |
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15V is the absolute limit according to Varta for their cells. That's a crazy level and it will be offgassing like mad by then.
https://dusj4r71pmvop.cloudfront.net/3815/3540/0001/FA_Owners_Manual_English.pdf
[Edited on 15/9/22 by coyoteboy]
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