Dumb charger

Yeah you are spot on there Phil , use the hydrometer ,if you have one , most of them nowdays have coloured areas where you cant go wrong , but as long as your Specific Gravity is 1.25 - 1.27 at around about 20 degrees celcius , you are not far wrong :)

Gday Pete,
I wonder whether the hydrometer is becoming a collectors item. It seems to be a forgotten piece of equipment - maybe because many batteries are becoming sealed, and maybe because the digital voltmeters are so cheap now. But it still gives better info about state of charge than anything else out there - provided you have a wet cell battery.

Yeah Phil , I agree with you on all counts , things have changed , I am glad I am retired now and dont have to keep up with a lot of the newer technology that is surfacing now :)

Andrew, any charger,(smart or dumb) will measure a low voltage initially, because theres a limit to how many amps the charger will put out. If a discharged battery will accept say 25 amps at 14volts, then a 6 amp charger will probably only read say 13.5 because they are not capable of putting out any more than 6 amps.

If you bought a 25amp charger (smart or dumb), it will deliver more amps and the voltage will be higher in the initial stages.

I use a switchmode 20amp, 13.8V power supply as a battery charger because I can leave it on indefinitely without damaging the battery, and they are cheap to buy, and I also use it as a powersupply when playing in the shed.

Phil there is a 20amp Xantrex Truecharge Multistage charger in the Karavan that seems to take ages to get the charge up after the batteries get to 85%. It seems to spend most of it's time in float. There are a series of LEDs that give an indication of the level of charge.

Mind you there are 10 35amphour AGM batteries to charge up. Not that they are allowed below 55% charge.

Why is it so?

Just like phil says. The voltage will drop because the light duty charger cant keep up. Eventually the battery will charge up and provide resistance and the amps (current) will fall off and the voltage will rise.

John, as your batteries charge up they will present resistance as above and unless the charger can step up the volts the last bit of charge will take time. Look at it like pumping up a tyre. A little pump can provide the pressure (voltage or electromotive force) but not a lot of volume (amps or current). The pressure in the tyre rises and presents resistance to the last amount of volume needed to achieve the pressure required. The last few pounds take the longest. A big powerful air supply will overcome a lot of the resistance and fill the tyre quicker. Like power = pressure times volume or volts times amps.

20 amp charger is pretty good but 350 amp hours is a big hole to fill thus the situation you describe.

I hope that sounds ok. Things that make sense to me I often have trouble describing.

Owen

10 35AH batteries and I think it would be a battle to charge them properly at all as 10 batteries in parallel will fight each other for charge and one battery will reach charge faster than the rest and then force the charger to float thus all remaining batteries will suffer in capacity.
Eventually the weakest battery will fail and full down the next weakest one and a domino effect will prematurely fail all batteries.
You would be better place to throw out all ten and try and get your capacity through batteries in series and allow your charger to do an efficient job of charging which it cannot do in your present application.
Dont tyhrow them out till you kill them for cost reasons but when you do seriously consider investigating it before you replace them.
Ian

Hi JohnR, the set up you have is renown for causing problems.

Why the manufacture has elected to fit ten 35 amp 12 volt batteries is a mystery to me.

If you have followed this particular manufacturers instructions on the size of cable to run from the vehicle to the trailer you will have a double whammy as the cable stated is way to thin.

For a start, if I were you I would connect up the battery charger and then disconnect all the negative battery terminals but one.

Leave the charger in place till this battery causes the charger to switch to float then disconnect the first battery’s negative terminal, connect the second battery’s negative terminal and repeat till all the batteries have been charged.

Then and only then would I reconnect all the negative terminals and leave the charger float charge and maintain the all batteries at once.

Next, if your cable running from the front of the two vehicle is less than 6B&S ( 13.5mm2 ) I would strong recommend you replace the existing cable with much bigger cable and I would go thicker that 6B&S.

This is one time when an alternator will well and truly come into it’s own. Because an alternator does not monitor the battery(s) and the alternator’s voltage is not effected by the state of charge of any batteries connected to the system, an alternator can actually fully charge all the batteries you have with out you having to do anything more than go for a good drive BUT you must have adequately sized cable, positive and negative, running back to the trailer.

Cheers and best of luck.

Drivesafe the man wants to travel not spend all his life disconnecting batteries and charging them individually every time he stops his vehicle and is on the charger.

I concur you are correct in your independent charging advice but if as you indicate its a manufacturers fault it should be rectified for the benefit of the user not give the user a permanent job charging batteries.

Ian

One battery is not going to charge up to the disadvantage of the others because the others will keep pulling the charger and the first battery down. The voltage will not rise until all are full and the charger will keep on providing current. I think one problem in this scenario is when you get a dead cell somewhere and it shorts the circuit thus drawing away the current leaving u thinking the batteries are not charging. (also dead battery) Only way I can think of to check is disconnect all the negs or the positives and check each battery separately. God, those submariner electricians must have their hands full!

I reckon the ideal would be to have separate cells two volts at a time so you could single out the problem ones. It wont happen because of the cost and inconvenience. three cell batteries (6v) there are and I suspect the reason is for as above.

Thanks Obee, Drivesafe and Wheelybin for your constructive suggestions in answering JR's question for me. I was still scratching my head, wondering why they would use 10 x 35 Ah batteries. I think John runs a CPAP machine so needs the capacity.

Would it be an option to either
#1 use two chargers when hooked up to 240V, (separate the 10AGMs into 2 groups of 5) or
#2 use the bigger (110A) Christies Charger when off the beaten track.

Naturally I'm just guessing - I've had no experience with running heaps of batteries out bush.

Hi Phil G, one specific manufacturer supplies their vans, originally with a bank 10 x 35 A/H AGM batteries but I think they have now cut the number back to 7 or 8 and like you, I fail to see any advantage to this sort of set up, just loads of disadvantages.

The manufacture has had it suggested to them that this is not the best way to provide battery power but they just tell anybody trying to help them that the company knows what it’s doing and go to hell.

If I had one of their vans, as it is not only going to be unreliable, the rest of the gear they use also makes it extremely inefficient. I’d be ripping out the whole 12 volt system and starting a fresh.

Cheers.

Just to diverse slightly the price of lead has jumped 40% in three weeks . China has about 25% of the lead and not good quality and the supply of good quality lead to China from Western Australia appears top have been cut on so called environmental grounds so Chinese battery makers have problems so watch these problems exacerbate the problem and escalate the price of all batteries especially the Chinese ones.

At least the Australian good quality lead is still available in Australia.

Most battery prices in Australia rose on 1/07/07 and as of next monday some sellers are imposing a percentage surcharge which will be reviewed on a fortnightly basis.

THE BITTER TASTE OF POOR QUALITY LINGERS LONGER THAN THE ECSTACY OF A CHEAP PRICE..
Ian

I have a Charge Controller from Projecta, a BM140, that sits between a dumb charger and the battery. Works well enough for me. Have'nt seen them around for a while though.

If you up to a bit of basic electronic kit construction, Electronics Australia published an add-on regulator for the common Arlec 4A chargers in July 1997. Would probably work OK with any simlar low capacity basic charger.

I've had a Dick Smith version of this kit float charging our caravans' 2 x70 Ah AGM batteries for about six years now and it's worked perfectly. For such a simple kit, it's brilliant - it even has temperature compensation which follows almost exactly the battery manufacturer's table of float voltage Vs temperature.

Coudn't find it on the DSE website today but Jaycar still list it as Cat. No. KA1795 ($24.95) - but it shows as Out of Stock. Presumably this means it will still be available in the future. An email to their webiste would confirm.

Oh, for an edit function on this forum! For some reason, I repeatedly leave the "r" of "your" and don't pick it up on re-reading before posting. Apologies for this and all the other typos not noticed.