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Author: Subject: Is 14.8v too much?
Sanzomat

posted on 13/9/22 at 07:00 PM Reply With Quote
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

posted on 13/9/22 at 09:46 PM Reply With Quote
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

posted on 14/9/22 at 08:40 AM Reply With Quote
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

posted on 14/9/22 at 09:25 AM Reply With Quote
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

posted on 14/9/22 at 10:23 AM Reply With Quote
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

posted on 15/9/22 at 12:14 PM Reply With Quote
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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