charging batteries in parrallel?

[Steve B]

This is probably a simple one for some!!..but I am confused:P

I got 2 x marine pro 600 batteries set up in parrallel in my camper trailer. I have a projecta IC1500 (15amp smart charger).

I was wondering if I can leave the batteries in parrallel permanently with the charger attached to maintain the batteries while the trailer sits in the shed!!

IF so, do you connect the charger to 1 battery (clamps to + and -) OR connect the + clamp to the + terminal on one battery and the - clamp to the - neg terminal on the other battery??

appreciate the input!!.

Cheers Steve

[Dicko]

IF so, do you connect the charger to 1 battery (clamps to + and -) OR connect the + clamp to the + terminal on one battery and the - clamp to the - neg terminal on the other battery??

appreciate the input!!.

Cheers Steve


Lock in option B Eddie.


Pump them back up using the same terminals as it's being drawn out.

[oldboot]

If the batteries are the same type age and condition, you should have little or no problems operating them in paralell permanently....it may be wise however once in a while to seperate the batteries and charge them independently...and test them to make sure the are both healty.

If they are connected in paralell by reasonable heavy cables... connecting the positive to any positive and the negative to any negative that is directly wired to the batteries will get the job done

cheers

[Kleyny]

Im with oldboot.

neil

[Crunchy]

Agree with Oldbot too, have the same batteries in the boat, simply attach my 7amp smart charger to the positive and negative on any one battery and switch the selector to "1+2" and they both charge happily away. (I disconnect the VSR though). Oldbot is spot on, if one of the batteries is stuffed the charger won't pick that up so best to charge them independently from time to time.

[Steve B]

Thanks fellas..much appreciated.

Both the batteries are brand new..I want to keep them in good nick as long as possible...hence buying a decent smartcharger too. The projecta IC1500 is their top line smartcharger and was reccommended highly...possibly better than a Ctek (which is a bold call)..time will tell. $215. Same 15amp Ctek was $360.

Thanks again. Steve

[Razgo-]

Listening to nugget (Dave Downie)on 4BC a couple of weeks ago he said when you charge parallel batteries that once the first battery is fully charged it WILL NOT continue to charge the second battery.(i always thought it did) Someone rang in also and agreed and explained why.

this is in regards to when the batteries are being used in parallel iin the boat using the 1-2 isolator switch. They said every now and then to run the isolator switch on pos 1 only to ensure the other battery gets a charge.

perhaps this is different when charging directly with a battery charger though.

[Fishbait]

Stevo - I just brought the C-Tek Charger last week ironically. These are great. You can have adapter leads attached to each battery permanently, and some of the adaptor leads have indicator lights on them to show if the battery needs charging or not. Either way, when you want to charge, just plug it into the adaptor. Can leave and forget for months so C-TEK reckon. Was advised to charge one battery at a time, and have the isolator OFF. All the best mate, Darren.

[Steve B]

Listening to nugget (Dave Downie)on 4BC a couple of weeks ago he said when you charge parallel batteries that once the first battery is fully charged it WILL NOT continue to charge the second battery.(i always thought it did) Someone rang in also and agreed and explained why.

this is in regards to when the batteries are being used in parallel iin the boat using the 1-2 isolator switch. They said every now and then to run the isolator switch on pos 1 only to ensure the other battery gets a charge.

perhaps this is different when charging directly with a battery charger though.


Thanks mate,

that sounds interesting, and feasable too. If anyone can add to this, or explain a difference (if any) between the 2 types of setups ie the 1-2 isolator vs direct charging two linked batteries...I didnt think there was a difference when you switched to 1+2 but I haven't had a boat with an isolator on it.

Cheers Steve

[Razgo-]

from memory i think its the solenoid that cuts off once the battery reached its charge so it doesn't recognize the second one. but i am guessing since there is no solenoid when direct charging from a charger it should charge both.

but yes more clarification would be good.

[Steve B]

Stevo - I just brought the C-Tek Charger last week ironically. These are great. You can have adapter leads attached to each battery permanently, and some of the adaptor leads have indicator lights on them to show if the battery needs charging or not. Either way, when you want to charge, just plug it into the adaptor. Can leave and forget for months so C-TEK reckon. Was advised to charge one battery at a time, and have the isolator OFF. All the best mate, Darren.


Thank Dumpy, yeah I tossed up between the 2 . Which model did you get? Hey, I sold the frenzy!!...looking at importing a bass boat!!..watch out mate it will have pace!!!:P:D

Cheers Steve

PS: any S8's missing in your dept!!! ha ha, ;D;D

[rayken1938]

The charger relies on the voltage of the battery that it is connected to to govern the charging current so if you have 2 batteries in parallel and one of them is 13.1 volts and the other is at 12.4volts the charger will only maintain a float charge as it thinks that the battery is fully charged and the 12.4 volt battery will never be fully charged unless you charge it individually. ( See priviso below)
If you run both batteries in parallel all the time the voltage disparity should not happen but if you use one battery for the motor and the other for say your lighting you will end up with different voltages.
After saying all that if the batteries are left in parallel the higher voltage battery will eventually discharge into the lower voltage battery and the voltages will equalise. That is providing that both are in good condition.
Confusing isnt it?
Cheers
Ray

[finga]

Instead of looking at batteries as things that hold voltage or charge consider them as 2 fuel tanks in a truck.
Each tank is it's own entity.
The 2 tanks can be joined by a hose so when the motor is going each tank goes down at half the rate as if one tank was used.
Now when the tanks are empty you can fill them back up again at the bowser.
You can either fill them up individually if the connecting tap is turned on or turn the tap off and fill each tank separately.
Make sense matey??

Just consider each of your batteries as a tank in the truck, the hose between the tanks is the cable joining the 2 batteries, the truck motor is considered the lights etc in the camper and the smart charger is the servo diesel bowser nozzle.
Using a normal battery charger when the batteries are flat is like going to the servo to fuel up the tanks when the red light is on. The charge is put back into the battery
The smart charger is like a servo following you and giving you some diesel into the tanks when needed like if the truck sits in the sun for a month and some diesel evaporates....a battery will lose charge naturally too so you have connected the smart charger.
Seeing your going to be always using each battery together you are effectively just making one larger battery just like the hose joining the two fuel tanks is just making a larger tank out of 2 smaller tanks.
So if the two batteries are been discharged together as one you might as well charge them together as one.

So in short...option B

PS the best way to keep your batteries in good nick is to use them all the time.
Turn all the lights on every week or so and run the batteries down a fair bit before recharging. Hence the old saying...use it or lose it comes to light.
Some of the smart chargers have a discharge feature. I'm not sure of the one you have.

[Noelm]

finge has a better explanation, all this talk of solenoids and so on is not so, the two fuel tanks with a connecting hose is a perfect example, you could connect 50 batteries (or fuel tanks with connecting hoses) it makes no difference (sort of)

[Crunchy]

Listening to nugget (Dave Downie)on 4BC a couple of weeks ago he said when you charge parallel batteries that once the first battery is fully charged it WILL NOT continue to charge the second battery.(i always thought it did) Someone rang in also and agreed and explained why.

this is in regards to when the batteries are being used in parallel iin the boat using the 1-2 isolator switch. They said every now and then to run the isolator switch on pos 1 only to ensure the other battery gets a charge.

perhaps this is different when charging directly with a battery charger though.
This is why a VSR is a good idea as it takes care of this very issue. Shouldn't leave the position switch in "1+2" as you risk running down both batteries at once....i.e. no back up! (Obviously more important in a boat then a caravan). I run position "1" or "2" alternating between trips so both batteries get a workout once and a while (Although not often enough with these damn northerlies).

[Razgo-]

This is why a VSR is a good idea as it takes care of this very issue. Shouldn't leave the position switch in "1+2" as you risk running down both batteries at once....i.e. no back up! (Obviously more important in a boat then a caravan). I run position "1" or "2" alternating between trips so both batteries get a workout once and a while (Although not often enough with these damn northerlies).

thats it in a nutshell. i used to think both batteries were charging but this isn't the case at all.

[Noelm]

not all as clear cut as people are making out, refer back to Fingas description, the batteries are connected via cables, they discharge and recharge at the same rate, because they are directly coupled, just like the two fuel tanks with a hose between them, you cannot run one tank/battery down without the other keeping pace, one battery will probably not charge up then "stop" the charger from any further charging.

[Dicko]

, refer back to Fingas description, the batteries are connected via cables, they discharge and recharge at the same rate, because they are directly coupled, just like the two fuel tanks with a hose between them, you cannot run one tank/battery down without the other keeping pace, one battery will probably not charge up then "stop" the charger from any further charging.


Exactly. SteveB has said the batteries are in parralel on a camper trailer and asked how to connect his charger.

Why is everyone on about battery switches, solenoids or VSR's between them ??

Keep it simple. Just charge them as one, back into the batteries in the same manner as the current is drawn out. They will stay equal both in and out as they are effectively one 12v battery once parralelled.

and as oldboot mentioned, every now and then check and charge them individually for a look see.

Millions of batteries in endless applications all over the world live like this for their whole life. No need to complicate it.

[Geoff-]

PS the best way to keep your batteries in good nick is to use them all the time.
Turn all the lights on every week or so and run the batteries down a fair bit before recharging. Hence the old saying...use it or lose it comes to light.
Some of the smart chargers have a discharge feature. I'm not sure of the one you have.

great advice in general but I don't completely agree with the last bit. Lead acid batteries don't like being discharged completely, if you frequently try and use the last 20% of their capacity they will die an early death. Equally, if you leave them in the discharged state they can be completely cactus in a matter of 24-48 hours. Lead acid batteries sulfate when they are flat. nicad batteries (rechargeable AA's etc) do like being discharged before charging, it depends on the battery chemistry.

"Deep cycle" lead acid batteries are designed to be run down more than regular ones but they still don't like being completely sucked dry. the regular type are "starter" batteries and they are only designed for a short high current surge for starting an engine, they don't like being discharged past 50%.

in answer to the original question, your batteries will love you for it if your smart charger switches to float mode and maintains 13.5V across the batteries. this is the best way to store lead acid batteries long term if you are not using them.

[castlemaine]

Listening to nugget (Dave Downie)on 4BC a couple of weeks ago he said when you charge parallel batteries that once the first battery is fully charged it WILL NOT continue to charge the second battery.(i always thought it did) Someone rang in also and agreed and explained why.

this is in regards to when the batteries are being used in parallel iin the boat using the 1-2 isolator switch. They said every now and then to run the isolator switch on pos 1 only to ensure the other battery gets a charge.

perhaps this is different when charging directly with a battery charger though.

I heard the same thing and thought I was enlighten but now after everyone's comments I'm confused.:-/ :P

[Dicko]

The radio article, or someones interpretation of it is wrong. They may have been referring to a falied VSR in a dual battery set up or something. Not a basic parrallel set up.

In parrallel, 2 of the same capacity batteries in the same condition will send out or recieve current equally.

If they were referring to a regular dual set up via a switch of batt1, batt 2 or "both" then it will end up like this (parrallel) when in "both"

Here's the first random pic I found of 2 12v batts in parrallel.

How could one of these charge one and not the other. ??




http://www.bigboytoysonline.com/RVMods&Articles/Batteries/Images/2x12VoltinParallel.gif

that didn't work, try another one

http://www.teamkiss.com/battpara.jpg

[finga]

great advice in general but I don't completely agree with the last bit. Lead acid batteries don't like being discharged completely, if you frequently try and use the last 20% of their capacity they will die an early death..
That's why I said a fair bit and not completely.......

People get too technical and complex for these battery things.
Batteries are relatively simple things, and as such, should be thought upon as simply as possible.
Treat them like the battery in your car. Check the water occassionly and use the buggers.....

[Crunchy]

Hmmm, well I won't be charging in parallel any longer....yesterday I decided to take my own advice and have a look at the batteries seperately, they are both the same type and age etc and I charge them in parallel.

I took them out of the boat and gave the outside a good clean, checked electrolye levels, "no load" voltage and then put them on the smart charger to see what it thought. One battery was perfect, fluid levels good, holding its charge and only needed a quick top up from the charger....the other needed quite some attention....electrolyte levels were low in a couple of cells, the residual voltage was low and it took an over-night charge to restore it back to full charge.

The learning for me is that even if the batteries are the same age , condition etc charging in parallel can lead to the wrong conlcusion, i.e. that both batteries are good. I will now be charging them individually just to be sure. Basic stuff for those in the know but a learning curve for me and perhaps others.

Cheers
Crunchy

[oldboot]

You were indeed wise to do the checks.

if the situation was allowed to continue one of the batteries probably would have failed.....if it was then allowed to continue further it quite llikely would take the other one with it.

after you have " maintained" your batteries, you may still be able to use them in paralell.... but you would be keeping a close eye on them, hey.

There is no substitute for regular battery maintenance.



cheers

[finga]

Hmmm, well I won't be charging in parallel any longer....yesterday I decided to take my own advice and have a look at the batteries seperately, they are both the same type and age etc and I charge them in parallel.

I took them out of the boat and gave the outside a good clean, checked electrolye levels, "no load" voltage and then put them on the smart charger to see what it thought. One battery was perfect, fluid levels good, holding its charge and only needed a quick top up from the charger....the other needed quite some attention....electrolyte levels were low in a couple of cells, the residual voltage was low and it took an over-night charge to restore it back to full charge.

The learning for me is that even if the batteries are the same age , condition etc charging in parallel can lead to the wrong conlcusion, i.e. that both batteries are good. I will now be charging them individually just to be sure. Basic stuff for those in the know but a learning curve for me and perhaps others.

Cheers
Crunchy
If one was going then the other would not be too far behind it if they are of the same age, type etc etc etc etc.
Time to change both.......

[Crunchy]

If one was going then the other would not be too far behind it if they are of the same age, type etc etc etc etc.
Time to change both.......

nope, now that they have had some individual attention they are both good as gold, the point is that in parallel, oncce the charger sees one battery is fully charged it doesn't know that the other one still requires more charging, it simply goes into maintainence mode and the other battery is left only partially charged, if you only ever charge in parallel (Like I used to) I guess the impact on the partially charged battery gets worse each time. Again basic stuff for those in the know but I learn't something.....

[oldboot]

Finga's thaugts are reasonable........if you were depending on these batteries relacement may be a reasonable choice.

The explanation of why the two batteries charge differently may be... um.. a little simplistic....... but for most it is a reasonable explanation.

one thing that can cause uneven charging in identical batteries is temperature.

The internal resistance of a battery , and its ability to accept charge are effected as its temperature increases.....if one battery is better cooled than the other in the pair......the worse off battery may not charge as well and have a shorter life.
so if a battery pair are fitted one behind the other for example the back battery may not get as much cooling as the front......purely speculation in this case but, one explanation for uneven charging.

or more likely..........just variation in tolerances......I have not heard of anybody in "camperland"....cycling and selecting matched batteries from a larger stock.

cheers