Lesson in measuring battery health

Submitted: Friday, Apr 22, 2005 at 20:26
ThreadID: 22300 Views:2472 Replies:3 FollowUps:6
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This is a lesson in believing what you learn from this forum, and that machines that go beep are not always the ants pants.

Two Exide Extremes bought 3 months ago to run in series in my 24v landcruiser. Purchased from KMart Auto on a 25% off everything day in search for a bargain.

Alternator pushing 60amps at 24v and charging set at 28.4v - lovely.

I pull 12v supply from the centre tap and have a Redarc Charge equaliser to ensure both batteries are recharged equally, and also a Redarc Isolator to ensure I don't flatten them with the fridge etc.

I could never get the batteries to charge properly or hold their charge. This got worse over time and eventually I could only get a minute or so of fridge running out of them before the isolator kicked them out at 12.2v. (Redarc changed the setting down to 12.2v from the normal 12.6v for me)

I got the batteries checked at 3 different places with the electronic gadgets they use. All said the batteries where in good shape.

Yes, they had adequate volts in them, but when I would measure them with hydrometer they were way way down into the red, and I couldn't run the fridge, so clearly there was a problem.

Man with tricky electronic gadgets say there is no problem with battery, must be vehicle.

Tim says, but what about hydrometer reading?.

Man with tricky electronic gadgets say they trust tricky electronic gadget over $5 old fashioned gadget any day.

Times this by three and Tim's getting real frustrated.

Clearly there is a problem, but no one was looking for a simple solution.

I visit the 12 Volt shop in Welshpool WA.
Nice man there says 'well if hydrometer says battery is low, then it's low'
Halleluja, this man must read the forum I thinks. :-)

Nice 12 Volt man says:
Where batteries a matched set? Must be matched set to instal in 24v application otherwise will never charge. A matched set is charged equally before installation.

Tim is suddenly enlightened and says:
No, batteries were not a matched set. Kmart Auto don't know about such things. Can this be fixed?

Nice 12 Volt Shop man says:
Yes, boil them up for while.
And you know - he was right!

I bought a 10amp manual charger, had them charging for 12 hours plus, and watched with joy as they bubbled away happily and the hydrometer rose and rose to where is should be.

I'd been charging them with a charge and leave automatic charger that worked as it should but did not boil them to increase the SG of the acid. Somehow a controlled overcharge at 15v rejuvenates batteries and is a useful addition to maintaining good battery health.

So - as one of the other forumites says - a volt meter is not always an accurate measurement of battery health - the hydrometer is. It's reassuring to buy an automatic charger that we know is not going to damage our batteries, but ones with an overcharge function, or a manual charger that you keep an eye on, has great merit.

Hope this helps others in battery despair.

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Reply By: Exploder - Friday, Apr 22, 2005 at 21:19

Friday, Apr 22, 2005 at 21:19
Ants pants. That a good one never heard it before.

I can’t believe that 3 so called battery or auto electric experts could of got it so wrong.
AnswerID: 107891

Follow Up By: Tim HJ61 (WA) - Saturday, Apr 23, 2005 at 00:35

Saturday, Apr 23, 2005 at 00:35

I won't mention the locations, no need to make my point.

Auto One spare parts shop. Run by old salts who I've never found to be wrong or unhelpful before. Couldn't explain problem, but to their credit they did say their machine indicated the battery needed a charge up as one battery was 'a bit' low.

Battery World. Specialist Battery shop. Dismissed hydrometer as being unreliable and not worth anything. 'Much prefer to trust this machine than that' This was even after I showed him the hydrometer in action with the float hardly moving in the red area. His hand held machine showed the CCA rating was higher than the rating on the battery and in good condition.

KMart auto where I bought the batteries. Big beefy floor machine said batteries were in good condition, exceeding battery specs. Needed a top up charge only, but they said the machine says that about all batteries.

Auto lekky. Described problem and what I had already repaired, checked etc. He said there must be a current drain somewhere. Offered to book vehicle in and check it over which was a fair enough response. I booked it in, but then cancelled after my next visit below.

12 Volt shop. Battery and solar specialists. Described problems. About half way through my description he asked about balanced pairs, gave me the tip about buying a manual charger, and told me what to do. Too easy and right on the money.

What it has shown to me is that even people who you'd think/hope would know stuff just got it wrong, way wrong. Maybe only one of them had good listening skills!

But the thing that alarmed me was the dismissal of the hydrometer as being an unreliable tool, when in fact it was the only accurate tool for my problem, and the usefulness of hydrometers is repeated by every discussion on this topic on this forum. If we know this stuff, how come they didn't??

FollowupID: 364763

Reply By: Big Woody - Friday, Apr 22, 2005 at 21:54

Friday, Apr 22, 2005 at 21:54
Hi Tim,
Can you explain how you have pulled 12 volts from your 24 volt system. I have always been of the understanding that the only way to do this properly is with a 24v-12v reducer. This in effect dissipates the extra 12 volts not used through heat sinks.
I have had a couple of 24 volt Nissans and without the use of a voltage reducer, you will gradually drain the battery that you have connected the accessory to, down to the point where it cannot receive a charge.
Hard for me to explain as I am no auto electrician and maybe someone else can explain more clearly, but as the batteries are in series, I think the battery with the lowest amount of charge will only receive charge until the higher battery is fully charged and stop there. Then each time you drain it a bit more, it will only receive the small amount of charge again until it is fully drained.
What type of fridge do you have? I think Waeco will run straight of 24 volts as well as 12 volts.

AnswerID: 107895

Follow Up By: Tim HJ61 (WA) - Saturday, Apr 23, 2005 at 00:17

Saturday, Apr 23, 2005 at 00:17

There is always a great deal of discussion on this topic.
What I have learnt is that your points are entirely correct, well mostly!.

The two 12v batteries are in series. The battery that feeds the 24v system, starter etc is called the high battery, the battery whose -ve goes to ground is called the low battery.

You can get 12v to power anything you choose by taking the power from the -ve pole of the high battery, or the +ve pole of the low battery and the earth/chassis/-ve pole of low battery. Given there is a solid cable between the two it is only a matter of convenience which pole you connect to.

Discharge is not the problem - recharging is.
Without extra electronics, the alternator charge overcharges the battery with the highest voltage, eventually boiling it dry to destruction, and not charging the battery with the lowest voltage, eventually flattening it beyond redemption. I've not read a clear description of why this happens, some give the example of the charge having to go 'through' one battery before it gets to the other. When my 15 yo lets me get to my regular computer I'll post some links to good sites that try to cover this complex topic.

Certainly one answer is to instal a reducer. I do not think they work in the way you describe, but can't explain how they do work so will leave that to others. The problem with a reducer is that you are limited to the current you can pull through it. My original one was not current protected so I eventually found it stopped working even though it was fused. I think it just cooked itself. There are also concerns about whether they handle running things such as fridges - others may disagree.

The biggest thing for me was that mine would not charge an aux battery, so I was not unhappy when it died. I think they would work well for low current items, radios etc., but have my doubts in complex systems.

Adelaide company Redarc make a charge equaliser which you connect between the two batteries. It effectively halves the voltage on the input side and evens out the voltage/charge between the two batteries, overcoming the problems inherent with pulling 12v from the centre tap as it's called. My Charge equaliser is rated at 20 amps, and that looks after the battery voltage equalising very well.

I can pull whatever current I like from the centre tap to run fridges, invertor, HF radio etc etc, and importantly use it to charge an aux battery to the same voltage as each battery in the 24v array. Any unequal charge between the two 24v batteries is then balanced at the rate of 20amps through the charge equaliser and all batteries remain happy and balanced as long as you run the engine for long enough to replace the charge at 20 amps. For example, you may be used to recharging with a 60 amp alternator, and have to rethink times incorporating the lower capacity of the equaliser - 20amp.

There is no risk of 24v being applied to my 12v equipment as the feed is coming off a 12 v battery.

I have an old 29l Engel - over 20 years old now. Runs of 12/240v. No intention or need to change it over, but if/when I do, I'll be making sure I get a 12/24 optioned appliance as the current draw is a lot less on 24v.

I trust this answers your question.

FollowupID: 364762

Follow Up By: Tim HJ61 (WA) - Saturday, Apr 23, 2005 at 01:09

Saturday, Apr 23, 2005 at 01:09
Click on this link for an extensive discussion on this topic.

12v and 24v Discussion

FollowupID: 364766

Reply By: Member - Woodsy - Saturday, Apr 23, 2005 at 07:46

Saturday, Apr 23, 2005 at 07:46
Hi Tim,

Won't go into the technical discussion but will comment on K Mart.

Bought an Exide Extreme from K Mart Burwood Vic for my boat. After about 3 months it was , I believed, not up to performance.

Tried charging but couldn't get good readings on the hygrometer, in fact some were well into the red.

Took it the aformentioned K Mart and the Store Manager told me that hydrometer readings were not a true indication of a batterys condition and he would check it with his fancy electronic machine. Fancy machine results were that the battery was "better then new".

Still not satisfied and took it to Exide factory in Mitcham. "Ya battery is stuffed! Here is a new one!"

So much for K Mart and their fancy machine and their competence.

Lessons learnt:
Hygrometers don't lie.
K Mart do lie.
Buy my batteries from my auto elec mate from now on (just did recently).

(It is a pity though that K Mart's prices are so good).
Happy 4 wheeling


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AnswerID: 107925

Follow Up By: Member - iMusty (VIC) - Saturday, Apr 23, 2005 at 08:43

Saturday, Apr 23, 2005 at 08:43
Kmart offer 100% money back.

Learn from here & buy from there.

I mean ... Get great advice/work from auto elec but still buy non specialist parts from Kmart.

I dont expect ONE BIT OF ACCURATE INFORMATION from Kmart. Just cheap prices.

And Kmart Burwood being open 24/7 is very convient. Just gotta watch that bloody Blackburn Rd. gate closing early. Lol. I've done many a U-turn there.
FollowupID: 364778

Follow Up By: Charlie - Saturday, Apr 23, 2005 at 12:56

Saturday, Apr 23, 2005 at 12:56
I've owned a hydrometer and three battery meters with varyiing results so I guess peoples opinons are based on their personal experiences
Maybe it's the hydrometer, or the battery or the operator but I found it totally useless.Next was the Jarcar votage meter which worked well untill I blew it up(no reverse polarity protection),then the cheap Dick Smith battery meter which ago was totally useless and lastly the min kota meter which seems to work OK .

Regards Charlie
FollowupID: 364788

Follow Up By: Tim HJ61 (WA) - Saturday, Apr 23, 2005 at 14:25

Saturday, Apr 23, 2005 at 14:25
Hi Charlie,

What was useless about the hydrometer?
They're a little bit fiddly to use I know, but was it inaccurate in giving you an indication of battery health?

A voltmeter is really easy to use, and it seems that as long as the battery is in good condition and isn't playing tricks such as mine were, then a voltmeter may be adequate in telling you the real state of charge in your battery.

All depends on what information you want to get from the equipment.

FollowupID: 364793

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