Must have jump pack

[Giles]

hi

no, electricity is lazy like me and will always find the shortest route, you would have to put plus on battery 1 and negative on battery 2. If you don`t do this you will get lots of weird and wonderful issues, i see it every day with big banks of batteries installed on boats and ships.

Giles

 

[Gav Peter]

But installed like that it would maintain the two batteries Giles?

 

[uHu]

no, electricity is lazy like me and will always find the shortest route, you would have to put plus on battery 1 and negative on battery 2. If you don`t do this you will get lots of weird and wonderful issues, i see it every day with big banks of batteries installed on boats and ships.

Giles is right. But, on a car the situation is slightly different:
1 - The trickle charge on a car battery is very low, after a while, and the current (both charge and consumed by alarm etc) is close to zero (in practical tems). Therefore the voltage difference between the two is very small. Also, the cable between the two batteries is thick and short, with a very low voltage drop. (rated for starter current) Then add this to the next point:
2 - The batteries are connected in parallel all the time, not only when the charger is connected/charging, and that will even out any differences.
3 - For a car with 24 V start (and 12 V parallel normal), the positive pole on one battery and negative on the other will during start either be at 24 V relative to each other, or at zero V (shortcircuited). Neither of these situations would be very much liked by the charger (although the 24 V into the output might be OK, depending on the construction).

The most important issues for vehicles with two batteries are that the two are equal in construction and age, preferably a matched pair; and that the connection between them are in perfect condition, both terminals and cable. Still, if it is convenient, and you don't have 24 v start (or never start with the charger connected), connect one pole to each.

If you, on the other hand, charge the two batteries with a powerful charger (or booster) out of the car, where the interconnect cables might be smaller as well, there will be a considerable difference in charge level if both charger leads are on one battery.

For stationary batteries, (radio station, emergency lighting, navigational instruments, etc), the charger is actually the power supply most of the time; and there is a constant, high, charge voltage. Any small difference in voltage between the two (ore more) batteries will result in a permanent difference in charge level. This will accumulate over time and be detrimental to the battery's health and longevity.

 

[Giles]

hi there

I am going to be a pain here sorry,,size and types of batteries makes no difference when linking batteries up from the point of view if you can and if it will work. Simply 12 volts is 12 volts, doesn't matter what colour the battery is` what size, what age, nothing. (its good practice to keep things the same but there is no physical reason)

Think of it like this 12volts is the size of your wallet, some people have bigger wallets 24 volts

AH size is just like money, if you have 4x £5 notes you have £20,,if you have two £5 and one £10 notes you still have £20

From daily experience 2batteries will not equal out if you charge only like you may think, the reason for this is electricity moves at the speed of light, but absorbing electricity into a battery is very slow.

All charging equipment is volt sensitive and will turn off when the correct voltage is reached, if you have only connected one battery it will get charged and turn the charger off before battery 2 has had anything at all, then overnight battery 2 will leach of battery number one. What we find is all the volt sensitive kit on vehicles gets screwed up vehicles when you charge incorrectly in this way.

 

[uHu]

..,,size and types of batteries makes no difference when linking batteries up from the point of view if you can and if it will work. Simply 12 volts is 12 volts, doesn't matter what colour the battery is` what size, what age, nothing. (its good practice to keep things the same but there is no physical reason)
....
All charging equipment is volt sensitive and will turn off when the correct voltage is reached, if you have only connected one battery it will get charged and turn the charger off before battery 2 has had anything at all, then overnight battery 2 will leach of battery number one. What we find is all the volt sensitive kit on vehicles gets screwed up vehicles when you charge incorrectly in this way.

1:
Type, age and production series of the batteries do matter. Each battery, and in particular each type of battery, has it's own charge curve; voltage vs charge level. One battery is e.g. 80% charged at e.g. 14.33 volts. Another battery might be 100% charged at the same voltage. If you then continue charging, you will boil and harm the 100% battery. If you stop charging, the 80% battery will never be fully charged, and you will loose those 20% of that battery forever. There are very small differences in voltage for a relatively large difference in charge level between different types of lead acid accumulators.

2:
Battery 2 will leach off battery 1 only if they are not equal, due to not having the same charge vs voltage curve. We are talking maintenance/trickle charge here, and the charging will continue at a low current, with a consequential low voltage difference.


The ratio between the charge level and the voltage actually changes along the charge-level curve, or, put a different way, the curve is not a straight line. If the two batteries are not equal, the curves will be different, sloping and rising differently at different places. (I'm not sure of the correct expressions in English). That means that as the batteries are discharged over time, during use, the difference in charge level will vary between the two (as they are forced to keep the same voltage) as they move along the curve. - That is if the two are not equal.

But I can shut up now - if this is not interesting for the public.
The important thing is that if your batteries are connected i parallel, and not via some kind of smart device, it will affect the longevity of the batteries if they are not of equal type.

 

[Andy]

Ordered yesterday from the lovely Lauren, very efficient service and it arrived first thing this morning.

thanks Giles,

next time I need batteries you'll be my first port of call

Andy

 

[Gav Peter]

Thanks for the debate guys - my batteries in Muxley are a matched pair & same age, replaced a couple of months back, so presumably buying & fitting the trickle charger to maintain them as a pair would be ok...

 

[Giles]

hate to say this but uHu is not right here

we supply batteries to everything from cars to power stations. if you have a big bank of units you don`t do as uHu says and throw them all away just because you have one failed unit. You swap out the failed unit, even if the rest of the bank is 8 years old.

Voltage is voltage and amps Ah are Ah does not matter one little bit what the age or the is of the battery.

Batteries will aways charge equally if the the batteries are wired correctly and negative and positive at the opposite ends of the bank. The bank will then have ONE curve and not separate curves per unit if they are wired correctly.


anyway lets not talk batteries the only reason i buy LC is because batteries are bloody boring

 

[uHu]

... if you have a big bank of units you don`t do as uHu says and throw them all away just because you have one failed unit. You swap out the failed unit, even if the rest of the bank is 8 years old.

Big banks are normally connected in serial, to give you 24 or 48 volts, made up of individual 2 volt cells, or 6 V or 12 V in smaller banks. When you change faulty units, you always get the same technology cells as replacement, normally even the same make. It doesn't matter much though, as they are in series.

... Batteries will aways charge equally if the the batteries are wired correctly and negative and positive at the opposite ends of the bank.

Correct

...The bank will then have ONE curve and not separate curves per unit if they are wired correctly...

Correct, but this is also the problem. In a parallel connection, the two battery units are forced to have the same voltage, even if they internally have a different State of Charge. See the example in previous posting.

In any case, in practical terms, if you have two 12 v batteries of the same technology, even of a different Ah rating, they would work fine in a parallel connection. It's just that, depending on how different they are, they would last longer is they were identical twins. There are also many other variables affecting the batteries and their longevity.

If, otoh, you connect a traditional lead acid unit in parallel with a potassium battery or an AGM, they would not last long, as one of them would not be properly charged. With smaller differences, the difference in life span would be smaller. E.g. differences in the lead alloy grid structure (e.g. tubular vs lattice) would give a slightly different SOC curve.

(Potassium batteries are normally the "Silver Series" of the battery manufacturers, and often live longer, but require a slightly higher charging voltage, alhough not as much as AGM)

 

[Giles]

Hi sorry that's not right

if you connect a 12 volt 2ah AGM battery with a 200ah lead acid battery and wire them properly, when you charge and discharge their voltages will be the same as the two batteries have effectively become one. By the way there is no reason in physics why you can't do this, it's like saying you can't put 2 litters of water with 200 litters of water

you can only get different battery voltages in a bank of batteries if a battery is faulty or it is wired incorrectly

it makes no difference if there are 2 batteries in a bank or 200 hundred, any more than one battery is a bank, and any bank only has one curve and the properties of that curve are determined by the overall spec of the bank and not individual units

 

[uHu]

Giles, you are putting your finger right on the problem....

 

[warrenpfo]

Silly question but if i bought two could i then put one on each of the 12v batteries on a 24v start system and it should work??

Yes i know one seems to do the trick but just wanted to ask.

 

[stumog]

mine was dead flat the other day and i jumped the drivers battery off the one aux and it was fine started very quickly.

 

[uHu]

Silly question but if i bought two could i then put one on each of the 12v batteries on a 24v start system and it should work??

That should work fine, IF the chargers do not have any common ground for the 12 V side. I.e: check that the 0V (car ground) on the output is not connected to the chassis or to the earth of the input side (230 V ac).

 

[Olazz]

Had cause to use my jump pack on the 60 series...24v everything! Batteries proper flat. (2x 12's in series.)
Amazed it spun motor and fired up easily. Charger had been fully charged about 2 months ago, so obviously hadn't lost any of its punch.

Don't leave home without one!

 

[wobbly]

I have primarily been using mine to recharge other things via the usb port!

For overlanding its perfect, I can use my tablet at night without stressing about a flat battery, likewise phone which has viewranger on it.

I also use the light as a nightlight.

Top bit of kit!

 

[karl webster]

I have primarily been using mine to recharge other things via the usb port!

For overlanding its perfect, I can use my tablet at night without stressing about a flat battery, likewise phone which has viewranger on it.

I also use the light as a nightlight.

Top bit of kit!

Totally agree.

As a camping gadget for the use you have stated they are great. For a booster pack they are ok as a back up (just incase tool) ive already blown one up without hardly using it

 

[Chas]

ive already blown one up without hardly using it

What caused it to blow up Karl?

 

[karl webster]

Mine and daves has chas. Think daves had two blow. If you read the instructions it says something like you can turn the truck over but only for so many seconds. If it doesn't start you have to leave it so long between trying to start again. If it still doesn't start you can only attempt to start it so many times. Personally I think I blew mine for continuously turning motor over for maybe 20seconds. They are good but I don't think they are quite as good as made out. As said above though, for a back up power source they are good.

 

[Chas]

Mine and daves has chas. Think daves had two blow. If you read the instructions it says something like you can turn the truck over but only for so many seconds. If it doesn't start you have to leave it so long between trying to start again. If it still doesn't start you can only attempt to start it so many times. Personally I think I blew mine for continuously turning motor over for maybe 20seconds. They are good but I don't think they are quite as good as made out. As said above though, for a back up power source they are good.

Thanks Karl, I haven't needed to use mine yet but I'm sure if it didn't start straight away I would continue cranking so I must remember that if I do need it.