Battery Size Help

Thanks Tony,

I didn't realise that was a size, I thought that was a type. It has made my search a fair bit easier.

Beaut,

Cheers for that, I was hoping to get one before I head away for the weekend but looks like I will have to wait for delivery.

Thanks for the help.

nik

Just to clarify low capacity (I meant charging capacity, not amp hour)

"Low (charging) capacity AGM’s are poor value"

I thought all AGMs with plate shaped electrodes can absorb a maximum charging current of 25 to 30% of rated capacity @ 14.4 to 14.7V.
For this, temperature needs to be kept between 20 and 30 degrees for best charge acceptance.
I've come across manufacturers who don't specify a current limit below 13.8V because the battery itself limits the current draw sufficiently below this voltage.

From what I've read here in the forum and elsewhere, it is unlikely that an AGM battery will be sent into orbit by high initial charge current from an alternator.

Resistivity of the charging circuit provides significant current limiting.
Using heavy/short wires in an attempt to limit recharging times by a few percent can be counterproductive in the end.
And secondly, your alternator output voltage will drop somewhat under load, even if the alternator is rated 130A. By the time it supplies 130A, the output voltage would have dropped to around 13V anyway. And if you don't keep a close eye on your alternator's temperature it'll be toast at this current before you know it.

And why should a Concorde AGM battery be able to absorb much higher charging currents than other AGM batteries?
Just because they're more expensive, or do they use some kind of secret ingredient which makes the chemistry inside the battery perform some magickery?

And for the wet/flooded type which won't be damaged easily by ANY charging current, this doesn't mean that the battery will absorb this high current. In fact the charge absorption rate of flooded lead acid batteries is said to be less than the one of AGMs.

So, why exactly are AGMs other than the Concordes poor value?

Best regards, batterymeister

Hi Batterymaster – you raise a number of points.

“Manufacturers specifications” – if you go outside their limits whether they be makers of tyres, alternators, batteries whatever , then that's your business – They don’t produce these specs for nothing.

“Batteries limiting themselves sufficiently below 13.8 volts” – measure a heavily discharged deep cycle battery, discharged to 11 or 11.5 volts, connected to a high capacity current supply such as a modern 4WD’s alternator and see how much they suck in – you will be in for quite a surprise.

“Why should a Concorde AGM Battery be able to absorb much higher currents than other low quality AGM’s”. Better engineering - it’s not rocket science – check their specs. A Fullriver 100 ah AGM is limited to 20 amps whilst a Concorde is virtually unlimited.

If you need further information on fast charge rates for open lead acid batteries, websites such as RV Powersteam, will provide graphs showing typical curves of 100 ah batteries being charged at well over a 100 amps.

“Exactly why are AGMs other then Concordes poor value” – Concorde is not the only high quality AGM – you need to check their specifications.

Hi Dennis,

Speaking about specs:

Pull up their web site and start looking for battery internal resistance data.
You'll find, they don't publish the actual figure which may or may not raise some suspicion.
What I did find though, in the 'Technical Manual for Chairman', there are some good graphs (among other truly mind bogling stuff...)

Look at the orange coloured peukert plot for their 100Ah AGM.
Note the 1 hour rate of discharge corresponds to 65A, and the 20 hour rate corresponds to 5A.

Now scroll up to the discharge curves and locate the 1hr and 20 hrs ones.
To work out the battery resistance, locate the 'spread' of the two graphs during the first few percent of DOD, which happens to be around 0.6V.
Because this voltage difference is associated with a current difference of 60A (peukert plot), you can then calculate the internal resistance which works out to be around 10 milliohm (which is nothing out of this world really).
Note that this figure becomes somewhat higher as the 'spread' increases with DOD, meaning only a fully charged battery has the lowest possible internal resistance.

Up to now it was pretty boring, but now comes the hilarious bit:

On page 20, they write about 'in-rush' currents of 5C or 500A for their 100Ah product.
Yes, 500 Amperes.
Quickly multiply this current with 10 milliohm, and you'll get 5V, or around 7.5V if the battery was discharged.
Take the OCV of a totally discharged AGM @ 11.5V, and add 7.5V equals 19V.

I don't know if this means anything to you, but at this voltage/current you most certainly induce heavy gassing inside the battery, and quick heating - a potentially dangerous mix, and certainly damaging to the batteries health.

Now you might say, yes but my alternator is fixed to 14V, it never can get this high.
True, but not without problems if the current isn't limited to down to earth levels:

Take your discharged battery and apply 14V to it, which would result in an initial current of around 160A.
The Joule heating would be limited by your alternator output in this case (150A?), resulting in around 350W.
The losses of the internal oxygen cycle go on top of this, and you could be easily heating up your battery with 4 to 500W. Due to lead having a specific heat 33 times lower than water, it'll only take a minute or two for your battery temperature to increase by 10 degrees. Add high external summer temperature to this, and chances are you're exceeding the maximum permissible boost charge voltage for this temperature.

In fact, looking up the 'charge volt. versus temp' graph, it becomes apparent that at 110/43 degree F/C, your boost charge voltage is around 13.9V (border line), and float charge at around 13V.

What could make the situation worse:
modern alternators boosting the output to 14.4V for the first few minutes: makes your battery temperature rise higher yet, due to the longer duration of the current peak until the charging runs into the (higher) voltage limit.
On the other hand, fixed volt. alternators will damage this battery just as quickly as it'll overcharge not only during the bulk charging, it'll do so on float as well - quite a bit actually.

Last but not least, battery life is reduced by 50% for every ten degrees over 25 - you choose.

To add to your recommendation of 'check their specifications' - I agree totally, but may I add, that you also should take some dubious claims with a grain of salt.


Best regards, batterymeister

Hi Batterymaster.
You comment that in regard to Concorde’s specifications that “you should take some dubious claims with a grain of salt”.
If it comes down to credibility between you and the engineering data supplied from a company that provides high quality batteries to medical authorities, airline companies and western armies then there really is no choice is there?

Following your logic,

you can take anything for granted from someone just because they're selling to large institutions.

And why do they sell to these sort of customers?
Are they the masters of the holy grail of battery science, or is it plain reckless use of misleading marketing spin.
Ever thought about methods of winning contracts in an otherwise level playing field?
Why is the web full of statements like 'their batteries have the lowest internal resistance', yet actual figures are nowhere to be found?
And when looking at a couple of their graphs, with some understanding of the subject it becomes obvious that there is nothing extraordinary about their batteries' performance.

I could plonk quite a bit of relevant scientific material on the table, and go on interpreting, in an an attempt to make things plausible to you.

You'd just respond by brushing aside some meaningful reasoning backed on real data, and come up with nothing in the end.

Why didn't you say in the beginning that you prefer spin over studying the subject, and that you've made up your mind and end of story.


Best regards, batterymeister

The 20A limit on a DC100-12 is based on a worst case scenario of 14.7V. If you monitor the amps vs volts of ANY battery charged from an alternator they will take almost everything the alternator can produce for about 5 mins then the voltage will rise to the (relativley low) output voltage of around 14V and the current will taper off very quickly.

No 100Ah battery on this planet can magically absorb hundreds of amps for any length of time without internal heating causing excessive gassing.

Dave (Fullriver Product Manager - Australia & NZ)

Dave, I don’t take anything for granted and I test all of my equipment to its limits before I go bush.
I have one of your batteries, a Fullriver DCG 100 -12.
It’s a very good battery, in its 3rd year and still performing like new.
As you know it’s a VRLA Gel and it has a manufacturer’s charging limit of 20 amps.
I have a 20 amp charge limiting charger between my 4WD’s 130 amp 14volt alternator, and the DCG 100 -12 battery, to keep its maximum charge within the manufacturer’s limit.
I recently run a load test on this battery (to check it’s ah capacity) – heavily discharging it to 11.25 volts.
I then put it on my current limiting charger and it drew the limit of 20 amps for an hour at just under 12 volts. It would have exceeded this charge had I not had the limiter to protect the battery. This doesn’t fit with your statement that the current will taper off quickly after 5 minutes. After the initial hour, I then limited the current to 15 amps until it was fully charged.
I have had a far bit of contact with battery suppliers recently and this has led me to the opinion that most salesmen at the retail level don’t know their product. You should do practical tests on your battery’s performance before making statements like this.
This thread is now getting very old and it will be of no interest to anyone other than yourself and Batterymeister – This is my last input on this thread!