12-24 VDC Question

Experiments are fun even it there is the occasional fire.

I sure myself sympathize since I have the same mental problem.

Tesla was a genius for sure since for some reason I understand how AC works and how to apply it, but get lost with DC for with AC I can make things happen and balance it all out going in my head 10,000 watts, needs a hundred amps.

Or a thousand watts needs 10 amps.

Basically it seems as if in DC you have to have lots of volts, but in ac you have to have lots of amps. There is this Ohms law thing...

Basically it seems as if in DC you have to have lots of volts

Basically it seems as if in DC you have to have lots of votes also.

You take one battery from column A, and one battery from column B. You can have won-ton or egg drop soup.

A double pole, double throw toggle, rocker, or relay that will withstand the charging rate will work. Just make sure you use a quality switch. The jumper can stay connected while charging.

The two center terminals go to the charger. Left to positive, right to negative.

The top terminals go to the 0 to 12 volt battery. Again left to positive, right to neg.

The bottom go to the 12 to 24 volt battery. Still left pos, and right neg.

I hope this helps. Good luck.

Isn't it that you have a connection on the negatives that runs across the two negatives, but you jump the positives to 'pole' connections?

One DC to add up volts is what, a parallel circuit, and what's the name of the other?

I've right now forgotten.

If you have all of the negative connections joined, you will have to disconnect the 12 to 24 jumper before charging.By using the double pole switch the jumper can stay attached.

In parallel you will add amps, with the same volts.

In series, you will add volts, with the same amps.

Now you have changed your mind I see about the center connection......Hmmmmmmm!!

It's the end of the day.. so instead of typing it all out I'll just link you to a web page that explains series and parallel (I'm lazy today).

http://www.engineersedge.com/battery/battery_series_parallel_connections.htm

The switch/relay option would work fine as long as the components are rated for what you intend to use them for.

Good luck!

Ohh.. and trolling motor battery chargers (deep cell ~2 amp) are not that expensive. maybe 30 bucks?

Thanks Guys, I really appreciate that

don

That is exactly right; the charger rating is the key!

Bobc, I may be wrong as with a diagram I might follow your reasoning better, but generally speaking, you cannot charge 2 series connected 12 volt batteries from a single 12 volt charger.....as you have the positive of one battery and the negative of the other connected together in the middle.....

The only way to do this is to disconnect that connection first.

Then:-

Either charge each separately or both in parallel, positive to positive, negative to negative....which can still bring MANY problems, its only theoretically a good idea.

The problem would be far simpler to fix if we had two lead acid batteries that use voltage charging, but all (or at least most) other battery types have current charging, and this is not quite so easy to organize as you might think.

Also, charge differences between the batteries would make possible that huge, dangerous currents run between them as they try and equalize out, when connected in parallel......

I personally would make, buy borrow, a 24 volt charger with intelligence, to charge the batteries "in situ", with temperature sensing at each battery......I am sure they exist, but I personally have never seen one.

An easier way would be to have two good quality chargers, connected one to each battery.....also price wise a good decision.

I would be most happy to learn (and see a simple schematic) of the way you would connect a 12 volt charger to both batteries with the center connection still in place......

Please educate me.

You didn't mention that the switch MUST be a break-before-make type. There do exist make-before-break switches, which would place a short across at least one battery during the switching process, and something would blow!

Yeah, something would blow! If you're lucky, one of the wires would melt before the battery blows a hole in your wall!

With one charger and two batteries, I don't see how both batteries can be charged while in circuit if the charger is originally designed to charge just one in circuit battery. For to get 24V the two batteries will be wired in series, your charger will produce a charging voltage of just one battery, 12V plus charge drive. Maybe you could charge one battery at a time while in circuit or take both batteries out of service and parallel them if the charger can handle two that way.

GA. Exactly my point too.

I thought that Bob C was using the DPDT switch to ensure that only one battery was charged at a time. Thus the discussion about having a break before make switch.

You can't have 'em in series and parallel at the same time (ok maybe in StarTrek it'll work)
So you need a failsafe switching arrangement which will disconnect the jumper and reconfigure the batteries for you. (also safely disconnecting the load) Don't rely on multiple individual switches or operators removing the jumper...you will just end up with a fire.

BobC may have already desribed such an arrangement for you_{....(but a diagram would probably help, and I can't be arsed to check it out)}
Del

This will give me a chance to show off my new drawing skills.

In the up position the charger will be connected through the lower contacts, and charge battery B. In the down position the charger will be connected through the upper contacts to battery A. Any quality switch that is designed for the charger's full current should be able to do the job.

A switch with a center "off" position would allow the charger to run with no battery connection. That might not be good for the charger. A good switch would never allow the three contacts to ever touch while in the transition stage.

I hope this is readable for all.

Thanks a LOT, that diagram is a BIG help, and Radio Shack had both 2 position, and center off, double pole, double throw, which I purchased several of each...

You guys are So smart..

Remember, I am the LED guy, anybody need help, If I know it, I will tell you..

Don

I hope you get that drawing framed and put on the wall.

Intaglio print method suits well that sort of drawing, as an art piece.

I coppied it off of a tatoo I have on my chest.

You should have used the one from your back! Its a far better circuit!!!

I still have problems copying it from the mirror.

This will not work as described.Look carefully at the schematic and you will see.If you do not see, abandon this project, it above your pay grade.

You would have to switch out the load while charging.

It sure looks to me like the un-selected battery will be charged in reverse! through the load, unless the pos-to-neg jumper is removed before charging.

I agree, one must be VERY careful in not doing that. Its one of my main worries too, though i think its probably mainly due to incomplete/missing descriptions.....hopefully!

Thanks Simple Mind.. these little lith ion batteries will only have a 4 watt use, at 24vdc.. However, your advise is taken well, and we are putting these in heavy duty solid, sealed aluminum boxes for safety as none of us want any explosions..

Don

GA for a simply brilliant, well written post. I would give you more GAs if the system allowed....I seem to be the only one that understood you fully.....

The circuit that Bobc showed will work perfectly well with Lead Acid batteries, but will just kill off any other ones.......

I personally feel that two intelligent 12 volt chargers (in one box if needed) are the only answer that will work reasonably well and not kill off both batteries in a fairly short time.

Current charged batteries need a REALLY GOOD QUALITY CHARGER. Nothing else will do.

Hello simple..

Well your diagram works, so far so good, no fires.. :o)

However, I do notice that a couple of times the voltage sensors, on my lith ion batteries have shut the battery off, but I think I might have touched the wrong wires, thereby causing that..

I will keep testing, and let you know how it turns out

Don

The system cannot be charged with the 24 v load connected. The suggested double pole double throw switch would do the job. The load will be off for the duration of charging.

...unless a proper 24volt charger is found......then the load can remain.....usually, but it can depend on the charger's design a bit too......and that we do not know about as of now!

Regards.

The only solution with your case:

1.) Charger capable to charge only one 12V battery

2.) Two 12V batteries

3.) Both batteries connected in Series to get 24V

4.) This 24V setup is in continuos use

Simple Solution is:

a.) Connect a crucodile clip to each out-put wire of charger; a black to (-) & a red to (+) one.

b.) Keeping in mind the polarities of Charger & batteries charge one battery at a time in turn.

Have a fine day !

Connect

Depending upon your intentions (unclear) in "a.)" you will either create a short circuit or did you mean to charge only one battery at a time?......which might work, but very unconventional.....

Of course it may be.

But normally the clips are mostly insulated & there is no chance of short circuit unless connected together.

Any how a caution is necessary as you pointed out.

Thanks

Yes, Just hook up bat A + n - terminal same as bat B as individual bat n leave jumper in place.

Still very unclear. Try to make statements that are clear and unambiguos or show sketch.

But if you meant charge "battery A" till full, then charge "battery B" till full, then I understand.....then don`t send the sketch!!!

If you mean that you can charge both batteries at the same time using a single 12 volt charger, then supply the sketch ASAP.

Whatever the scheme the charger will see the load if it is in circuit with the load on. If what was originally posted was to be a kind of UPS the batteries will be on float. In the various schemes outlined here the two batteries will be in series with the charger alternately in parallel with each. I do not see this as a workable proposition. Probably a 24 V charger is the optimal solution. Bioramani

In my opinion, the only correct (and foolproof) way is to disconnect the jumper wire and charge each battery separately and with a charger designed for LI ION batteries. They have a different charging rate than lead acid batteries. Your 12 volt battery will start out at 10.2 v and end at 12 v.

GOOD BUDDY: YOUR ANSWER IS YES ! ! ! JUST MAKE SURE YOUR POSS. & NEG. CHARGER LEADS ARE ON THE POSS. & NEG. POSTS OF THE SPEC. BATTERY YOU ARE CHARGING AT ANY GIVE TIME. SIGNED, AN OLD RETIRED POWER PLANT MAINTENCE TECH.

Lithium Ion batteries require PRECISE voltage, current, and charge monitoring conditions to avoid damage and/or destruction. Most modern LI battery packs contain a special IC to monitor battery conditions and communicate this data to the charger. IF the charger was designed for Lithium Ion batteries, charge each battery INDIVIDUALLY. SAFE charging in series OR parallel would require a specialized charger which I'm fairly certain you do not have.

If the charger was designed for batteries OTHER than the Lithium Ion batteries you HAVE, I suggest you reconsider this project before there is property damage and/or injury.

GA for a perfectly correct post, many thanks.

Just for clarity, when I stated "charge each battery INDIVIDUALLY", I was referring to each LI battery PACK. The cells inside the pack are all monitored by the internal IC which will usually disconnect the pack when a dangerous condition (short, large cell imbalance, cell reversal, etc.) occurs.

Why not use a 24V centertapped transformer with a diode for the positive and the diode reversed for the negative? A charger with 3 leads instead of 2, the centertap going to the junction of the batteries.

Hi Donald,

assuming that the lions are the same and that the charger is suitable for that type of battery. you can use this circuit which is typical of those used to get 24V for bow thrusters on 12 V boats. (rather more power than you would need i think!)

when the charger is plugged in it puts the batteries in parallel and disconnects the load. when the charger doesn't have power then the two batts are in series supplying 24V to your lighting load.

hope this helps

Chas

Goood Answer.This will work.No reverse charging of either battery, as in the previous sketch(#10)which will not work as intended or described.

At least in your house, the lighting does not blow fuses.

Chas

GA on this challenge! Note also that Donald can still use a 2P2T relay he seemed to accept but he can use a (MBB)"make before break" 12VDC failsafe relay (more available than 1P4T 110VAC relay) by connecting batt 1 to the 2 common relay inputs. The 12V coil would be across the input to his load & batteries. Batt 1+ switches from the load (NC) to batt 2+ (NO) for charging, and batt 1- switches from batt 2+ (NC) to batt 2- (NO) also for charging. As soon as the 12V charger is plugged into the batteries & load the relay will automatically switch over from the batteries being in series across the 24V load to the 12V batteries in parallel across the charger. The charger would have to be sized to keep the relay energized and charge the batteries or the batteries would take longer to charge. Hope Donald gets this.

Under NO Circumstances can he use a make before break relay as that will cause a short circuit and destroy the contacts on first operation.

Using a 110V relay makes better sense as a relay on the DC side will be powered by the battery unless a diode is added, which will defeat the program/sensing in the charger.

Chas

OOPS - You are so right. I meant a BBM (break before make) which is the standard. Thanks for the correction.

The 110 V coil in the charger means the relay must be part of the charger, so no easy "plug in the charger" solution. The charger can be adapted for the small drop across the steering diode.

Sounds like he has selected another course anyway!

A good reply but the drawing be ammended as below as the NC contact have the connected line on left so that it breaks on nergising of the relay:

Regards

Hi Hajee,

It actually doesn't matter which way the contacts are drawn, they still show as nc contacts which must perforce open when the coil is energised. However, I do agree that the way you have drawn them is more self explanitory.

Incidentally the two left contacts could also be one changeover contact, making this an ideal subject for an eleven pin "valve base" relay, since the charger will not have an output>10A.

OK

As you like

From the wording of the OP, I had presumed that the charger was correct for charging one of the battery packs alone. As such all I was doing was showing a way to charge each battery while leaving the remainder of the system intact. I also believe that for best results, a 24 volt charger would be best. But that is not the cards that were dealt by the OP.

(chocolate tea pot)?

In principal I tend to agree with you on that point.

But I also feel that two 12 volt chargers, one connected across each battery may not only be slightly better, but far, far cheaper as well, as 24 volt chargers for this battery type are to my mind seldom seen/expensive.....but maybe someone can prove me wrong!

WARNING WARNING DANGER WILL ROBINSON! Li Ion and Li Polymer batteries are easily destroyed and even can catch fire ( I know i've burned a couple ) if not properly charged and balanced. ONE use LiFe batteries, they are safer and less prone to catching fire ( also they have a longer cycle ( charge/discharge/charge/discharge etc ) life. You do need to get a proper charger for these batteries, especially LiIon or LiPolymer batteries that check voltage and prevent overcharging. I guess you could use a 24 volt charger but be careful, one method would be to bring out the 12 V wires frm each battery, and charge them seperately, using 2 12V chargers. Definately use LiFe batteries over LiPolymer.

I agree fully.

GA from me too...

OK, OK, already.. I hear you guys... and THANKS so much !

After playing with these Li Ion batteries, I have decided to make my application totally fool proof, from a user point of view.

I will keep the batteries separate, in two separate, solid aluminum enclosures, providing only one connection, in and out, and each battery box will indeed have its own, (proper from the factory) charger.

Then I will provide a Y adaptor so that 24vdc can be achieved externally by physically plugging into the in/out connection.

This will force the customer to only use the Y adaptor for obtaining 24vdc, and then removing the 24vdc cord, and then plugging into the same holes where the Y adaptor was to individually charge each battery from two, separate approved chargers..

Hopefully this will let those concerned sleep easier, and if the batteries fail, catch fire, whatever, it will NOT be my fault for sure.. and that's what insurance is for.. :o)

Thanks again for all the great advice, and the concerns, and warnings..

Cheers

donald

Good decision to my mind. Should also give all concerned peace of mind....

Nobody seems to have mentioned most Li-ion batteries have an internal thermistor to monitor the temperature while charging. This usually comes out on a third contact so charge current can be limited by the charger circuit if it gets too hot.

hmmm.

Please fuse each battery pack unless they have bulletproof internal protection. The fault currents from a rechargeable battery can be very high - enough to cause welding of switch contacts, fire or battery explosion.

Some Lion cells are only protected against short circuit by blowout system at one end of the cell which permanently disconnects one terminal. The cell cannot be used again if this happens.

http://www.sciencedaily.com/releases/2008/08/080807073753.htm

http://www.faqs.org/patents/app/20090233165