a question for the battery geeks

Submitted: Thursday, Jun 07, 2007 at 20:15
ThreadID: 46404 Views:1789 Replies:6 FollowUps:11
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G'day
Well i posted a post a couple of days ago on how my 2x100 amp hour DC batteries linked together, when on charge would charge for days on Boost charge, when they usually should go to Float charge after aprox. 24hrs. I thought it was the charger maybe, Bzzzz wrong. Tried charger on other battery and went to float charge fine. So i thought maybe one of the batteries is knackered. So i disconnected them from one another, tested them individually. One read 12.7V....beaut. The other 11.3.....bump bum. So i think , OK that battery for some reason has bleep itself. I decide to charge the 11.3V one by itself, guess what, the charger goes straight to float charge. This does not make sense, it reads 11.3V which is discharged. You would assume it would want to cop a real good charge on Boost mode. To confuse the situation more, i put the charger on the battery that read 12.7V, and it went straight to boost charge.
Any one with any explanations or ideas would be greatly appreciated.
Cheers
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Reply By: Member - Roachie (SA) - Thursday, Jun 07, 2007 at 20:21

Thursday, Jun 07, 2007 at 20:21
Makes no sense to me mate.....but I'd be getting the charger checked out, the multimeter checked out.

Failing that, .....................hmmmm............I simply dunno!!!!!!!

Sounds VERY bloody strange to me. Are you sure you didn't stuff up? Didn't have too many raspberry nips before doing the checks???? Sorry........ ;-))
AnswerID: 245465

Follow Up By: FREEZER - Thursday, Jun 07, 2007 at 20:42

Thursday, Jun 07, 2007 at 20:42
Nah mate thats tommorrow night. LOL
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FollowupID: 506494

Reply By: Derek from Affordable Batteries & Radiators - Thursday, Jun 07, 2007 at 20:27

Thursday, Jun 07, 2007 at 20:27
Hi Freezer

Are they wet cell batteries ?

Do a hydrometer test.

I would say you have a dead cell.

Regards

Derek.

AnswerID: 245467

Follow Up By: FREEZER - Thursday, Jun 07, 2007 at 20:41

Thursday, Jun 07, 2007 at 20:41
i did but i broke it. Is it common for a battery with a dead cell to read 11.3v, and go straight to a float charge. If so do i need another battery.
Cheers mate
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FollowupID: 506493

Follow Up By: FREEZER - Thursday, Jun 07, 2007 at 20:43

Thursday, Jun 07, 2007 at 20:43
Yes it is a wet cell batterry. AMPTECH is the brand
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FollowupID: 506495

Reply By: Grungle - Thursday, Jun 07, 2007 at 20:50

Thursday, Jun 07, 2007 at 20:50
Hi Freezer,

Are both batteries the same age and have they been paralleled together from the start? Sounds like the capacity of each is reduced but one more than the other so after they go to float and a load applied, the surface charge quickly dissipates and the battery shows its true state of charge.

Get the batteries load tested by a reputable company and if OK, I would suggest trying an equalisation charge to both whilst in parallel (please read up on this first before doing it as strict control measure need to be in place to prevent damage) and then give both a good charge with a 3 stage charger.

Regards
David
AnswerID: 245480

Follow Up By: FREEZER - Thursday, Jun 07, 2007 at 21:10

Thursday, Jun 07, 2007 at 21:10
yep might head down to battery world tommorow before heading off camping. Sounds like i may be up for new batterry though, cant have the beer going warm on me.
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Follow Up By: D-Jack - Thursday, Jun 07, 2007 at 23:31

Thursday, Jun 07, 2007 at 23:31
Grungle, I'm about to link 2 70amp/hr AGMs together, one will receive the charge and be parallelled to the other - what are these strict control measures you are talking about? The wire connecting positives will be fused each end.

D-Jack
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FollowupID: 506556

Follow Up By: Grungle - Friday, Jun 08, 2007 at 07:25

Friday, Jun 08, 2007 at 07:25
Hi D-Jack,

You can't do an equalisation charge on any sealed type of battery. This type of charge is for wet cell batteries only where you can take the caps off. You need to remove the batteries from the system and have them in a well ventilated area with the caps off - idealy in a place with access to water as when you do the charge the batteries will gas furiously and you will get some acid spillage from the top.

An equalisation charge is when you charge at boost + 1V (say around 15.5V) for approximately 2 hours and then let sit for around 24 hours. This is a common practice in battery shops and home systems is an option on some smart chargers. It is a process that is designed to shock the batteries and bring all the cells back to the same voltage as you do get some variences between the cells due to fluid differences, age, sulphation etc. It is commonly recommended that this take place every couple of months however literature varies with regards to frequency.

If anyone is to do this type of thing, either get your local battery shop to do it or if confident yourself, read up on this process first and make sure you understand what you are doing - remember acid burns so take the appropriate measures and please do not do this whilst your batteries are still installed in the van.

Regards
David
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FollowupID: 506579

Follow Up By: Mike Harding - Friday, Jun 08, 2007 at 07:40

Friday, Jun 08, 2007 at 07:40
>You can't do an equalisation charge on any sealed type of battery.

Sure can:

http://www.cdtechno.com/custserv/faq.html#charging

Mike Harding
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Follow Up By: Grungle - Friday, Jun 08, 2007 at 07:52

Friday, Jun 08, 2007 at 07:52
Well there you go Mike, so you can do it. I stand corrected.

Most of the literature that I have read (including the spec sheet for my Dynasty AGM's) says you can't as the batteries cannot recombine the gasses fast enough hence the batteries swell and deform the cases.

To cover myself then I should say to read the spec sheet for the batteries and see if they recommend that an equalisation charge can be done.

Regards
David
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FollowupID: 506587

Follow Up By: Mike Harding - Friday, Jun 08, 2007 at 07:57

Friday, Jun 08, 2007 at 07:57
>including the spec sheet for my Dynasty AGM's

Interesting. The spec sheet for my Dynasty (UPS12-310, wonder if we bought them from the same guy? :) gives an eq. voltage?

Mike Harding
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FollowupID: 506591

Follow Up By: Mike Harding - Friday, Jun 08, 2007 at 07:58

Friday, Jun 08, 2007 at 07:58
PS. iirc wet cell batteries like an eq. voltage of around 16V whereas AGMs seem to prefer (require?) about 14V5.
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FollowupID: 506592

Follow Up By: Member - Mike DID - Saturday, Jun 09, 2007 at 17:23

Saturday, Jun 09, 2007 at 17:23
Quote from http://www.cdtechno.com/custserv/faq.html#charging

"When is the DYNASTY VRLA battery to be equalized?
When a system is initially installed it is recommended that it be equalized at a voltage of 2.4 volts per cell average for 12 to 24 hours. "

That's 14.4 volts - the SAME voltage that every Alternator puts out !

Describing 14.4 volts as an Equalising voltage is truly strange.
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FollowupID: 506777

Reply By: Derek from Affordable Batteries & Radiators - Thursday, Jun 07, 2007 at 20:51

Thursday, Jun 07, 2007 at 20:51
Hi Freezer

It sounds like a dead cell. I would like to know the hydrometer readings of each cell.

Hydrometers are cheap. Please buy one and test.

Regards

Derek.
AnswerID: 245481

Reply By: Eric Experience - Thursday, Jun 07, 2007 at 21:29

Thursday, Jun 07, 2007 at 21:29
Freezer.
You have one cell that is open cct, when you place the charger on the voltage rises to more than 14.2 so the charger thinks the battery is charged and goes to float. This is a very common problem, any body who has anything to do with batteries would see this almost every day. sorry to say but you will be shopping for a new one. Have a good trip, Eric
AnswerID: 245490

Reply By: Robin Miller - Thursday, Jun 07, 2007 at 21:30

Thursday, Jun 07, 2007 at 21:30
Seems reasonable to me following on from your previous post Freezer.

Its also one of those little unstated reasons why a standard power supply can be a more useful tool than a complex charger particularly one that has no time settings in it.

In this case you have two devices and the complexity makes it harder to sort out which , or if both are faulty.

If you have the description of how the charger behaves under different load conditions (should be in manual ) we could probably help more.
(Brand model number may help to)

Even 11.3 is still not dead flat - and should be able to hold that voltage for a few minutes while powering a headlight globe or similar - this should tell you if have dead cell, while you hunt down a Hygrometer as Derrick suggests .

Robin Miller


Robin Miller

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AnswerID: 245491

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