Lesson in measuring battery health

Yep.

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??

Tim

Brett,

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.

Tim

Click on this link for an extensive discussion on this topic.

12v and 24v Discussion

Tim

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.

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

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.

Tim