BATTERIES IN PARALLEL

gandk · Senior Member

BATTERIES IN PARALLEL

Radar · Guru

I can understand that.

to answer your question honestly I can't.

Then again I do understand as long as they are similar quality ie glass to glass and so on.

Cloak · Guru

If you need higher capacity it's better to run two large 6V batteries in series.

Paralleling batteries can be a problem to downright dangerous if there's an internal fault in one of them.

That said many folks do run parallel 12V batteries with no apparent issues other than head scratching as to why they never seem to hold a charge for long.

As for different ratings, ages or types in parallel I would strongly suggest you get advice from a sparkie rather than forum advice.

Actually ask Philc, he's a professor of electrickery.

Cheers and stay safe.

Dougwe · Chief one feather

My understanding is both batteries must be of same style, size and age. Big Phil will set you ( and me ) straight for sure and if I am wrong he will send me to the naughty room AGAIN.

Woody n Sue · Guru

That's ok Dougwe the naughty room is vacant right now mind you the Fridge is empty
And I agree with your thoughts on the batteries
Philc come on down

Phil C · Guru

Thanks woody. Dougwe is off the hook too.

To answer the OP. It is probably not too smart to put different AH batteries in parallel. That also applies to new and older battery in parallel.

Reason for this is that the higher charged battery will try to charge the weaker battery, I have always been taught that parallel batteries should be the same AH and age.

There may be different opinions on this but that's the guts of it according to my training.

Cheers

PS: I forgot to mention TYPE as well, with so many styles and types on the market today I would start with two or three identical batteries. Remember in parallel we increase available current and the voltage remains the same, in series the voltage increases but the available current doesn't change.. Cheers

-- Edited by Phil C on Monday 29th of June 2015 07:39:51 PM

-- Edited by Phil C on Tuesday 30th of June 2015 11:30:02 AM

Dougwe · Chief one feather

Gee fanks Phil, buddy.

You asked a good question Kim and got the correct answer from he who knows. Well done.

Keep Safe out there.

Cupie · Guru

Battery theory for me is a black art (just like antennas) despite an extensive career in electrics/electronics. (from Tradesman to Technical Instructor through to the top level Principal Technical Officer 'till I realized that I wasn't really a Technical person, so I became a Manager & lived happily ever after)

If I have a battery question my first step is to refer to Collyn Rivers ..... Here is one of his articles on the subject ...

http://caravanandmotorhomebooks.com/interconnecting-batteries-in-series-or-parallel/

So we are in agreement with PhilC, but of course that is not the end of it.

Once you have two identical batteries to connect, the way you connect them to the load is also important it seems. From memory you take your feeds from the positive of one & the negative of the other, after paralleling the batts with heavy leads of equal lengths & good connections of course.

The experts will correct me if I'm wrong (there was an excellent article on the forum about this recently but I can't find it .. buggar).

Phil C · Guru

Cupie wrote:
Battery theory for me is a black art (just like antennas) despite an extensive career in electrics/electronics. (from Tradesman to Technical Instructor through to the top level Principal Technical Officer 'till I realized that I wasn't really a Technical person, so I became a Manager & lived happily ever after)
If I have a battery question my first step is to refer to Collyn Rivers ..... Here is one of his articles on the subject ...

http://caravanandmotorhomebooks.com/interconnecting-batteries-in-series-or-parallel/

So we are in agreement with PhilC, but of course that is not the end of it.

Once you have two identical batteries to connect, the way you connect them to the load is also important it seems. From memory you take your feeds from the positive of one & the negative of the other, after paralleling the batts with heavy leads of equal lengths & good connections of course.
The experts will correct me if I'm wrong (there was an excellent article on the forum about this recently but I can't find it .. buggar).

Go to the top of the class Cupie, spot on

Aus-Kiwi · Guru

I have done it in the past for short times . ( 24v starter batteries & 6X6v house ) When battery terminal breaks or battery damage etc..
It's just that efficiency is only as good as the older battery.. I have never mixed battery types ...

-- Edited by Aus-Kiwi on Monday 29th of June 2015 11:29:04 PM

greyhoundtom · Senior Member

Bugger looks like once again I have stuffed up, and would not have if only I had read this thread first. :(

I have just purchased a 140 AH battery in order to place it in parallel with an existing 5 year old 100 AH currently in the van in order to boost the overall amperage available for both the 12 volt devices in the van and the running of an inverter to power a couple of 230 volt items off grid.

Looks like I will have to ditch the existing battery.

There again in the situation I find myself in now it would not worry me unduly if running these two dissimilar AH batteries in parallel over a period of time of say 12 months the 100 AH battery came off second best providing it wasn't dangerous to the extent where the possibility existed that the smaller of the two was going to go into meltdown.

So now after stuffing up my question is ..... can I run these two batteries in parallel without it actually being dangerous and possibly causing a fire?

Cheers, Tom

sandsmere · Guru

Tom, go and talk to a qualified auto electrician !!!

gandk · Senior Member

We are travelling to Townsville on Friday to firstly have our son (an electrican, not an auto electrician) look at the problem, and if he cant tell us what we need he should know someone who does, because as stated previously we don't trust any tradesmen in Mackay. In the mining boom they all became, not only, slack but very greedy. I don't mind paying decently for good work but not for bad workmanship and that's if they turn up at all.
But thank you all for replying I always figure too much information is better than none at all and I am learning about a lot of subjects.
Thanks again
Kim

Jaahn · Guru

Hi gandk,

The short answer to your question is YES OF COURSE YOU CAN run these two batteries together.

There will be no problem or melt down if the old battery is in reasonable working condition. It is not an ideal configuration but that really just refers to the long term life of the batteries. In your situation they will work OK IMHO and do just what you wanted them to do. wink

Really it is just like having a big horse and a small older horse pulling together, each just does what it can. biggrin There is no need to see an auto electrician or anyone else really. Just do it.

my two cents worth jaahn

03_Troopy · Guru

sandsmere wrote:
Tom, go and talk to a qualified auto electrician !!!

Lots of luck there. Most of them still subscribe to the theory that leaving a battery sitting on a concrete floor will make it go flat. biggrin

And I agree with Jaahn on this one. The only problem is you need to be vigilant and have some way of testing the condition of the older battery because eventually it will degrade to a point where it shorten the life of the other battery, or possibly damage it. Unless you can do that it's probably better not connecting them together for any length of time.

-- Edited by 03_Troopy on Wednesday 1st of July 2015 08:31:33 AM

greyhoundtom · Senior Member

Thanks guys you have put my mind at ease. :)

In the main I expect the current situation to possibly only continue for around six months or until such time we are 100% sure that the way of life we are about to embark upon is exactly what we wish to do. If and when that occurs there will be some money spent to change the whole system over to lithium and solar.

Hopefully proffesionally done. Lol

Cheers, Tom

Phil C · Guru

I agree with Jaahn as well, there will be no catastrophic failure, however the life of the combination will be shorter due to my reasons as stated above.

At over $300 for an AGM 120AH battery I would think the wise advice is to extend their lives as best we can. That's just my humble opinion. I also have little faith in some auto electricians, I have seen their training schedules... say no more

Cheers

iana · Guru

I am following this subject with interest, looking at getting a van made. My thoughts are 2 x 6 volt batteries sounds good, but what if a cell goes on one, you have no power at all. Charging two 12v batteries can cause problems, fouling the charger. Why not run as dual batteries on a boat with a Col-Hersee switch. 1- both-2, charge one battery up 100% then switch over charge the other, work off one, until it runs down, then change over to the other, works on boats why not on vans?

-- Edited by iana on Wednesday 1st of July 2015 07:26:26 PM

oldtrack123 · Guru

gandk wrote:
I did do a search on "Dual batteries" but really didn't convince me of what I am seeking. Can you have 2 batteries of different AHs. Eg we have a Full river AGM 120ah, can we put another in of say 100ah? My husband couldn't lift the 120ah into our boot-too heavy. We had to get the kid next door who goes to the gym to do it.
Kim

HI Kim

The quick answer is YES, you can have batterries of different Amphr capacity connected in parallel ,but they should be the same type

Parallelling batterries is a Very common practise

Batterries have been & will be paralleled for years & years.

Most trucks have parallel batteries to get the power to start the engine

In fact Every such battery consists of multiple batteries [cells] in parallel

Batteries intercharging & discharging depends on BATTERY voltage NOT Current rating!!

The main points are in the connections

Each interconnect SHOULD be the same length & the same sized cable circuit

The charging source/s SHOULD have the pos lead connected to the pos of one battery &the neg to the neg of the other battery.

The load Pos & neg should also be connected the same battery terminals as the charging cables

This is not so important with light loads & low charging currents, but can be with very heavy charging currents or loads

The charging source will see ALL the batteries as just one big battery just as it would with a massive single battery

ALL the connections to the batteries MUST be kept CLEAN metal to metal contact & TIGHT to avoid contact resistance.

The disadvantage of Parallel batteries is if one deveopes an internal short or current leakage it will pull it's mates down with it But that can occur no matter what type or rated ,or aged batteries are used.

If any sign of unusual loss of capacity is noted , each battery should be separated charged individually

Then see how it long holds its charge.

Again that applies even if new batteries of the same age, Type ,Brand or current rating are used.

Batteries of vastly different ages are best not paralleled ,as age can be a factor in developing internal leakage & short circuits

A prime cause being metallic sludge settling in the bottom of individual cells

PeterQ

-- Edited by oldtrack123 on Wednesday 1st of July 2015 11:00:16 PM

oldtrack123 · Guru

Jaahn wrote:
Hi gandk,
The short answer to your question is YES OF COURSE YOU CAN run these two batteries together.
There will be no problem or melt down if the old battery is in reasonable working condition. It is not an ideal configuration but that really just refers to the long term life of the batteries. In your situation they will work OK IMHO and do just what you wanted them to do.
Really it is just like having a big horse and a small older horse pulling together, each just does what it can. There is no need to see an auto electrician or anyone else really. Just do it.
my two cents worth jaahn

DITTO smile biggrin

And give each all the feed it wants & away he goes

PeterQ

-- Edited by oldtrack123 on Wednesday 1st of July 2015 10:56:14 PM

Peter_n_Margaret · Guru

What PeterQ said.........

Cheers,
Peter

Jaahn · Guru

iana wrote:
I am following this subject with interest, looking at getting a van made. My thoughts are 2 x 6 volt batteries sounds good, but what if a cell goes on one, you have no power at all. Charging two 12v batteries can cause problems, fouling the charger. Why not run as dual batteries on a boat with a Col-Hersee switch. 1- both-2, charge one battery up 100% then switch over charge the other, work off one, until it runs down, then change over to the other, works on boats why not on vans?

-- Edited by iana on Wednesday 1st of July 2015 07:26:26 PM

Hi iana,

This thread has got another life, perhaps because batteries are our life blood these days biggrin as they are on boats also !!

You can do many things but most people just like to put in a decent battery or two and not have to fiddle with any thing again. So the switch seems just work to most people. hmm If you wish to have insurance then sounds good to me. My wife would say "why are you always fiddling with those bl**y batteries " wink wink Of course the connections usually need a bit work over time.

The 2x big 6volt would be the way I would go probably if I wanted that capacity. The chances of a cell failing in quality batteries is not high. disbelief

Jaahn

in transit · Senior Member

Glad that Iana asked the question about a switch. I have one of these from boating days in the shed somewhere and was considering using it instead of replacing a year old 120W battery. I don't mind the fiddling so think that is what I will do

iana · Guru

As I understand it, battery chargers of today ( 7 or 8 stage) are very smart, unlike the chargers of yester-year that just poured amperage into a battery relatively uncontrolled. Todays smart chargers analyse the batteries condition, reconditioning, removing sulphide crystals, mixing up the electrolyte to get rid of layering etc. How do these smart chargers cope with a series of batteries wired in parallel, each battery being different in type or condition.
This is why I also mentioned the switch, so that the charger is only working on one battery at a time, charging and or reconditioning each battery to bring it up to its best spec. At work I always disconnect the batteries on the trucks and charge each one individually. I use two "Projecta" 35A chargers and quite often notice they will be working differently, even though the batteries are paired, same type, but one will have 12v being pulled off it for accessories.
So if a similar charger is charging a pair or more in parallel, will it work on the condition of the best battery, an average of them all, or take the battery in the poorest condition as its benchmark.

03_Troopy · Guru

Good point iana, firstly batteries in paralell should be of the same type, AGM, wet cell, gel etc. Although the chargers these days are smarter than old types, they can only see the the resultant battery configuration across the terminals. That is they will see an averaging of the total battery bank. This is not ideal for the individual batteries and is the reason why for optimal performance and battery life, you should try and match the batteries as close to possible to each other in construction and condition.

As for your situation with truck batteries (I assume they are connected in series to give 24V) rather than pulling 12V for one of the batteries, a better solution is to use a 24VDC to 12VDC converter to supply the 12V accessories. The reason is that it loads the batteries more evenly and if battery/start isolators are installed, removes the risk of possible reverse voltage being fed back to the 12V accessories when the isolator is switched off.

Phil C · Guru

iana wrote:
As I understand it, battery chargers of today ( 7 or 8 stage) are very smart, unlike the chargers of yester-year that just poured amperage into a battery relatively uncontrolled. Todays smart chargers analyse the batteries condition, reconditioning, removing sulphide crystals, mixing up the electrolyte to get rid of layering etc. How do these smart chargers cope with a series of batteries wired in parallel, each battery being different in type or condition.
This is why I also mentioned the switch, so that the charger is only working on one battery at a time, charging and or reconditioning each battery to bring it up to its best spec. At work I always disconnect the batteries on the trucks and charge each one individually. I use two "Projecta" 35A chargers and quite often notice they will be working differently, even though the batteries are paired, same type, but one will have 12v being pulled off it for accessories.
So if a similar charger is charging a pair or more in parallel, will it work on the condition of the best battery, an average of them all, or take the battery in the poorest condition as its benchmark.

yes yes and yes iana,

When I was in the airforce we had two major types of batteries lead acid and alkaline (mainly nickel cadmium, or NICAD). I spent a lot of time in battery maintenance in at least 2 of the squadrons I was posted to. We would "set" our chargers at the 10 hour rate which was one tenth of the rated AH capacity of the battery for lead acid and charge for 10 hours or until the specific gravity of the electrolyte rose to a charged level.

NICADS were charged in steps of current.

Enough theory, I still have a lot of learning when it comes to the new batteries, AGM etc. The new chargers are brilliant and actually condition the battery to extend their lives. If we look after these suckers we can expect a longer life and good service from them.

I still stand by my best practice in putting the same AH, brand and age battery in parallel. Despite the fact that nothing catastrophic will happen, if we follow that best practice and not discharge an AGM more than 50% of its rated capacity, the batteries will give a long and reliable life. A good 5 or 7 step charger will be a great investment as well. You don't need a 100 amp charger to do these batteries, a 20 amp will do the trick (and easier on the pocket).

If a cell "goes down" which is unlikely in todays construction methods, there will be less capacity and voltage. Batteries are made up of cells 2.2 Volts each in a lead acid, connected in series (internally) to make up the 14 volts at the terminals, therefore it follows that the most likely scenario (although rare) is a cell will short circuit and act as I have stated above.

Things to be careful of when these batteries are in operation:

If the case gets too hot to touch, turn off everything and get an expert to check the system, most modern day battery chargers have mechanisms to prevent this "thermal runaway" situation. Sealed batteries vent into themselves so we don't have to breathe in hydrogen gas.

As has been previously stated, these are our lifeline of electricity when out in the sticks, so it follows we do the very best we can to keep them happy.

I suggest anybody interested google batteries and find a palatable (no geek speak) site to do some learning.

Cheers

oldtrack123 · Guru

iana wrote:
As I understand it, battery chargers of today ( 7 or 8 stage) are very smart, unlike the chargers of yester-year that just poured amperage into a battery relatively uncontrolled. Todays smart chargers analyse the batteries condition, reconditioning, removing sulphide crystals, mixing up the electrolyte to get rid of layering etc. How do these smart chargers cope with a series of batteries wired in parallel, each battery being different in type or condition.
This is why I also mentioned the switch, so that the charger is only working on one battery at a time, charging and or reconditioning each battery to bring it up to its best spec. At work I always disconnect the batteries on the trucks and charge each one individually. I use two "Projecta" 35A chargers and quite often notice they will be working differently, even though the batteries are paired, same type
{1]but one will have 12v being pulled off it for accessories.
So if a similar charger is charging a pair or more in parallel, will it work on the condition of the best battery, an average of them all, or take the battery in the poorest condition as its benchmark.

H

In that situation there will obviously be problems without of balance in the batteries& really NOT a good idea!!

It is not what is generally considered a parallel bank, ,which means both charging & loads are common to ALL the parallel batteries

As Troopy has said you would be much better of with a 24Vto 12V dc converter.

In fact, I strongly suggest you consider that.

Your system relies on you manually checking on battery SOC & then trying to balance the charge in both , but you could easily end up reverse charging the 12V pick up battery with normal 24V LOADS discharging the 24V bank

Especially if those 24V loads are high current LOADS.

THAT applies irrespective of battery type size etc

PeterQ

03_Troopy · Guru

This page illustrates the reverse voltage to 12V equipment situation.
Reverse polarity 12V equipment

Baz421 · Guru

I agree with Phil C in regards to "matching" batteries.

I like Phil had heaps of batteries that I looked after in Melbourne, mid winter etc to start Deutz gen sets.

The gen sets took up to 1 min to start in freezing conditions very often so very hard on batteries and need regular very heavy charging individually.

One mistake I made on my boat with 3 X 12V bats in parallel was not replacing the whole lot at once,,, ie they took it in turns to fail and often you didn't realise a failure until you wasted hours charging the 3 in together in situ.

This cost me heaps more money over the years as the batteries ran a 12V danfoss fridge in the boat 24X7 sailing out of Darwin.

So my recommendation is bite the bullet and replace em all.

I just bought 4 for the van and have 2 home still OK and 2 a bit wasted after nearly 8 years, but I now look after batteries a lot better than I did on the boat.

-- Edited by Baz421 on Friday 3rd of July 2015 11:19:21 PM

Phil C · Guru

Further to what PeterQ has said, if you have a bank of ONLY 12V parallel batteries then a charger equal to the ten hour rate of the total AH capacity may be quite large and produce rather high currents. From memory (and kindly correct me if Im wrong) the AH capacities are added when in parallel.

If the batteries are in series/parallel combination, it may be best to either get a 24 volt charger as a 12 volt will be useless or charge them as separate items, again more work for you.

Once a bank of batteries have been charged the modern chargers will condition them rather than just provide a trickle charge. Im going to recant what I said earlier and say a switch between banks would not be such a good idea, the switch would need to be large and able to switch large currents.

Because we had very large capacity batteries (even to make 24 volts) we charged each as a separate item as we didn't know which aircraft they would end up in. The aircraft internal wiring provided the 24 volt connection (set them up in series). That only applied to lead acid batteries as we could make up 24 volt battery "boxes" for alkaline batts, each cell being 1.2 volts (NICAD).

Im not sure why a caravan would have or need a 24 volt system in the first place. Keep it simple with 12 volt batts in parallel, most things are built for that combo.

Cheers

Knowledge speaks, but wisdom listens.