Charging 12v Battery from 24v supply

[Justme]

1, The "190" is the "Cold Cranking Amps" ( CCA ), a number mostly used in USA to rate how good the battery could be at starting a car/bike on a very cold day.

2, At that rate, a completely flat 19AH battery would take 10 hours to recharge.

3, cuts off charging when the batteries reach 13.7v,

Mostly good advice but those 3 points need comment.

1, For deep cycle use you really want a battery that does not even have a CCA rating. They are just not suitable & will die quickly if used as a deep cycle bat.

2, Its not as simple as dividing the capacity by the peak charge rate. Not only do you have to allow for the temperature you also need to allow for charging efficiency. Fully charging a lead acid battery can take a very long time (think 24 hours to do the job properly any thing less is a compromise). The charge rate will drop quickly once you get to about 80-90% SOC (State Of Charge) so over the 10 hours you will not have replaced the 19ah never mind the extra you needed to.

3, A voltage cut off of 13.7 will NEVER get the battery to full 100% SOC. You need to get to around 14.4-14.8v & hold it for a few hours (its called an equalise charge) dep on which type of lead acid the battery is to over come the resistance to charge & finish the chemical reaction.
I am guessing that its a bad translation as 13.7v is the float voltage once it is full & not the cut off voltage.

 

[rtbcomp]

Numax do a range of batteries that can be used for deep cycle or starting.

 

[Justme]

Numax do a range of batteries that can be used for deep cycle or starting.

Do you believe all the adverts / marketing that you see?

Check out the number of cycles that they can do & see how quickly that they drop off as you get to real deep cycling levels.

 

[rtbcomp]

These guys seem to like them

http://forums.lr4x4.com/index.php?showtopic=69708&st=0&p=596217&hl=numax&fromsearch=1&#entry596217

 

[Justme]

For some reason that link wont open, so I will guess that they use them in the main for winch batteries which is almost exactly the same use as a starter battery.

Speak to people that actually use them as deep cycle like live a board boaters & off gridders (Oh that would be me then as we have no grid supplied mains) & you will find a completely different picture.

Ah link just worked & I was right its mainly for winches.

I am sure you realise that they might use the winch once or twice a day for a week or weekend & then not use it for weeks & weeks. So in a 2 or 3 year life they only do 100 odd cycles. Yet in true deep cycling you could be doing a cycle every day or two. Watch how quick a battery starts to fail if its not a true deep cycle one.

 

[rtbcomp]

I suppose it's a case of something being dual purpose is never as good as something being designed specifically for a single purpose.

As the OP doesn't want the starting current, I'd agree he'd be better off with a dedicated deep-cycle battery.

 

[awemawson]

Proper deep cycle cells have an amazing longevity. I have a 24v bank of them in my flatbed 'works truck' - (a minature milk float). I bought it s/h and it had been left unloved by the previous owner for over a year with no charging and the cells were flat to less than a volt per cell. I charged them and used it for a while. As a matter of interest I did a capacity check, discharging them at the 10 hour rate into a large dummy load plotting voltage & current against time. They had a capacity of over 90% of original rating. That was five years ago, and since then it's had another year in storage with only one charging session followed by three years in use, and I have no reason to suppose it's capacity has decreased significantly.

 

[Delgado]

Still not exactly sure of your specific needs, due to not knowing how many of these 12v pumps you have, how often they are used, how low their batteries will get drained, whether you want to recharge them only when the truck engine is running, how long the truck runs versus when is the next time the pumps need to be ready,

what capacity and health the truck batteries are...

I'll try and answer your questions as best I can....

There are 2 pumps on each vehicle (1 litre nissan engines), the pumps (normally only one at a time) are used all day when the vehicles are out, but that could be all day every day for a month or only once or twice a week, it varies.

Often I find that the batteries are drained to the point where they wont start the pumps.

I would prefer it if they only charged when the engine was running, although travel time from job to job is normally only about 1 hour each way, so perhaps not enough charging time?

The truck batteries are normally isolated when not in use, so they nearly always have enough charge to start the vehicle, when they don't I put them on charge as soon as I can.

Been looking at those solar battery chargers that you mentioned, they look interesting and reasonably priced as do the caravan relays and split diodes, but as you said, I just need to find out if they'll work with a 24v input to charge a 12v battery. If not then I might have to go for the significantly more expensive dc/dc charger option, although it looks like 10 amps is the minimum output that they do, which may be a bit more that I need.

Thanks everyone for the input.

 

[madkayaker]

an alternative option might be to fit a 24V to 230V inverter to the truck that could be used to power other things like cordless tools chargers/ work lights etc and then you could use a standard battery charger that could also be used in the workshop if the pumps are not out for a while etc. if you got a big one then it could run 110V tools or get a 110V version and use 110V battery charger

 

[Justme]

although it looks like 10 amps is the minimum output that they do, which may be a bit more that I need.

It wont force feed the bats at too high a rate. The bats will only take what they need so dont worry about the min charge being 10amps.

 

[Delgado]

an alternative option might be to fit a 24V to 230V inverter to the truck that could be used to power other things like cordless tools chargers/ work lights etc and then you could use a standard battery charger that could also be used in the workshop if the pumps are not out for a while etc. if you got a big one then it could run 110V tools or get a 110V version and use 110V battery charger

Good Idea, an inverter would certainly be more versitile, and I could probably get all the bits (including a 240v charger) for less than a DC/DC charger. I'm thinking that I'd connect it up after the trucks isolator so that it's not running when the trucks not in use, although I think I'd need some way to stop it draining the trucks batteries, ie, when the trucks parked up at the job and not isolated/ batteries are being charged/tools being used.

Not sure about is how many watts I would need and a couple of other things, going to have a bit of a draw up to see how I'm going to do it and then post up my ideas.

Thanks

It wont force feed the bats at too high a rate. The bats will only take what they need so dont worry about the min charge being 10amps.

Great info, thanks.

 

[eddie49]

A 24v-to-240v inverter will probably only drain a quarter of an Amp from your truck battery, until the chargers/tools/lights etc connected to its output side are powered up.
So these pumps are actually driven by 1-litre Nissan petrol engines, and the 12v "motorbike-size" batteries are used for their starter motors? And ignition? And they don't get recharged - so there are no alternators on the engines?

 

[Delgado]

A 24v-to-240v inverter will probably only drain a quarter of an Amp from your truck battery, until the chargers/tools/lights etc connected to its output side are powered up.
So these pumps are actually driven by 1-litre Nissan petrol engines, and the 12v "motorbike-size" batteries are used for their starter motors? And ignition? And they don't get recharged - so there are no alternators on the engines?

The engines have alternators, and the main pump that's normally used is not so much of a problem as the spare (although they still go flat from time to time). I guess the simple answer is just to remove and charge the spare battery regularly, but that's not always an option. I suppose I could just put a 12v starter pack on the vehicles, but it looks a bit unprofessional starting them that way, so I'm really after a hastle free way of keeping them charged.

 

[Shox Dr]

What about fitting an Anderson socket to the leads.take off when not in use and keep on either an old forklift charger, or a mutli bank charger. A lot less hassle

 

[the snooper]

what you require is

one of these

and

one of these
they did do another that would switch between batteries once the first was fully charged

 

[rtbcomp]

what you require is

one of these

and

one of these
they did do another that would switch between batteries once the first was fully charged

No you don't. As previously stated (Eddie49, post #6) you need about 14v to charge a 12v battery, 12v won't do it.

There seems to have been confusion in this thread, some of us think the pumps are driven by 12v batteries, but it now seems that they are engine driven, with 12v starters on the engines.

In the latter case, you don't want deep cycle batteries, but ordinary 12v car batteries.

 

[the snooper]

right then scrap that

so what do we have

engines with 12 volt starters
but 24 volt altenators

if thats the case then just use 1 of the batteries for the starter motor but leave to be charged 24 volt

 

[rtbcomp]

right then scrap that

so what do we have

engines with 12 volt starters
but 24 volt altenators

if thats the case then just use 1 of the batteries for the starter motor but leave to be charged 24 volt

Not quite

We have a 24v supply from the truck enghine and engines on pumps with their own 12v batteries, so the OP is looking for a means of keeping the 12 batteries charged from the 24v vehicle battery.

 

[the snooper]

do these engines stay on the truck if so take a feed from 1 of the truck batteries do away with auxillery batteries

 

[rtbcomp]

do these engines stay on the truck if so take a feed from 1 of the truck batteries do away with auxillery batteries

Not ideal, if you use one of the truck 12v batteries it will become more discharged than the other in the pair, which will upset the balance when charging them.

Another idea may be to fit an extra 12v alternator to the truck engine and use that to charge the pump batteries. I know some of the Landrover mob use this method to charge winch batteries instead of installing a split charge system.