lead acid battery question...

[jim gilmore]

I got a question but not sure where to get competant answers. In my other hobby I use 12 by 10 amp hour batteries.
I'm trying to figure a way to solar charge them and here is my question...
Assuming I have 4 batteries, does it work like a 12v 40 amp battery if i connect them in parrel to charge them ?
I'm wondering if I could say connect them 1234 and on day 1 draw from #1 while the others remain charging. then day two I use battery #2 and so on. Each day I use a different battery to work with. And the other 3 charge.
Would this work assuming they are all 12v 10 amphr batteries ?

[Clancy Arnold]

Jim

I would NOT recommend paralleling the 12 Volt lead acid batteries as they will try to equalize and draw current from any battery that has a greater voltage even if that battery has less actual charge in it.  you could go ahead and series charge three while the fourth is being used.

This will require about 42 volts from the charger.  This will require about 96 solar cells in series. 

In All Seriousness, I recommend that you do not do it as you are playing with lethal voltage / current levels!

Clancy 

[dave siegler]

If you want to charge in parallel, you will need a way to prevent the strong battery from charging teh weak ones.  You could use a power diode on each battery to prevent battery to battery current flow, but that could be problematic also. 

[Howard Rush]

That sounds like a good idea.  You could use wimpy diodes, because they would only carry the charging current.  You could keep all four batteries hooked up to the charger all the time if you want to, and put the load on whichever battery you want.  How can one draw this here?  I tried with keyboard symbols, but it's even cruder than my CAD program.

                  
                    

[Paul Smith]

Jim

I would NOT recommend paralleling the 12 Volt lead acid batteries as they will try to equalize and draw current from any battery that has a greater voltage even if that battery has less actual charge in it.  you could go ahead and series charge three while the fourth is being used.

This will require about 42 volts from the charger.  This will require about 96 solar cells in series. 

In All Seriousness, I recommend that you do not do it as you are playing with lethal voltage / current levels!

Clancy 

Good advice.  They don't call it THE SILENT KILLER for nothing.

[jim gilmore]

ok, two questions here.
1- whats wrong with the batteries trying equalize. Especiall since I've been told it's easier to fill batteries when they are under 80% full ?
2-Why will it require 96 volts when in paralle  the total voltage of the 4 batteries is still just 12 volts...
or 13. something to charge....?

[Tim Wescott]

ok, two questions here.
1- whats wrong with the batteries trying equalize. Especiall since I've been told it's easier to fill batteries when they are under 80% full ?
2-Why will it require 96 volts when in paralle  the total voltage of the 4 batteries is still just 12 volts...
or 13. something to charge....?

1 - because then when you take a battery out of the charger, you won't be sure if it's all the way charged, unless you've verified that the whole group is up to full charge.
1a - because you should control the charge current to the battery for its health, and you can't do that when all are paralleled.

2 - Not 96 volts, 96 solar cells.  And that's for the recommended three batteries in series.

The right way to do this would be with three or four chargers, all running from your solar cell bank.  But they'd have to be pretty smart chargers, to take the best that the solar cell had to offer and not over tax it.  Alternately, get a solar cell system that charges its own battery and run three regular 12V input battery chargers from it (like Tritons).  You'd have to get one that's smart enough to shut down if the sun goes behind the clouds long enough for the solar system's battery to run down, and if that happened you'd have to start the charge cycles again, but it should work.

[Tim Wescott]

Jim
This will require about 42 volts from the charger.  This will require about 96 solar cells in series. 

In All Seriousness, I recommend that you do not do it as you are playing with lethal voltage / current levels!

Clancy 

42 volts is hardly lethal, unless you get it in just the right place _and_ your skin is wet.  And "lethal current" is a pretty smoky concept when you're at low voltage levels -- you just don't get lethal levels of current through your heart unless there's enough voltage to drive it.  Even a 12 volt car battery will drive enough current through a metal watch band to leave you scarred for life -- but it won't kill you.

Playing with 42 volts and giving it the proper respect is less hazardous than playing with model fuel, or those spinning steak knives that we use to propel our airplanes.  You can touch 42 volts and you're OK if you don't hug it, you can short out a 42 volt supply and get sparks and smoke.  But splash a tank full of fuel on your shirt then torch it off and you're in a world of hurt.

[jim gilmore]

ok, but if I'm using a 10-15   watt panel do I need to worry about cell count ?
Second question is when In an rv there is only 1 charger for a bank of batteries  correct ?
Do chargers go by the overall amphours of the bank or each battery ?

[Howard Rush]

I was able to make a crude drawing of Dave's idea:

[Paul Smith]

ok, but if I'm using a 10-15   watt panel do I need to worry about cell count ?
Second question is when In an rv there is only 1 charger for a bank of batteries  correct ?
Do chargers go by the overall amphours of the bank or each battery ?

That's rich !

Drive an RV and make Al Gore happy by solar-charging your model airplane battery.

[dave siegler]

ok, two questions here.
1- whats wrong with the batteries trying equalize. Especiall since I've been told it's easier to fill batteries when they are under 80% full ?
2-Why will it require 96 volts when in paralle  the total voltage of the 4 batteries is still just 12 volts...
or 13. something to charge....?

1)  Because you will take life out ofthe stronger battery.  If the stronger battery is constantly discharging well the weak one will kill it.

2) First of all you can't chearge a 12 battery with 12 volts.  You need about 2.3V/cell to charge or 13.8volts( 2.3*6) .  You need to place that voltage across each battery.  

Leathal.

Electric power sources can hurt you in many ways.  Under 50 volts, it is not easy to have electrictry flowing thought your body, but there is a lot of stored energy.  A short circuit from a watch band or ring can make a lot of heat and burn you badly.


If it were me I would use a diode on each battery to prevent battery to battery current flow and leave them connected all the time.

  

[jim gilmore]

ok, first off I understand that
I need 13. x to charge.... that's up to the charge controller to put out.
Solar panel on most sunny days should make plenty of volts...charge controlly lowers it down.

As for voltage concerns only connection points would be moving battery around. not totally rewiring.
As I said it's not an airplane...my actual use is a small puffer dry washer.. I mine for gold.. not really caring about al gore the wack job...

It's far easier to transport a 20# drywasher ,shovel and a small batter than a 75# lb battery.

[Pinecone]

http://www.ednasia.com/article-7565-hazardousvoltageprimer-Asia.html

[Howard Rush]

I mine for gold.. not really caring about al gore the wack job...

If you believed in science, you'd probably know how to make a circuit.  Nevertheless, I'd use Dave's suggestion.

[jim gilmore]

believing that al gore is and wack job and believeing in good science and good politices are not neccessilary the same or exclusive.

Looking at the article on dangerous voltages .,.what does that have to do with multiple batteries hooked up in parralle where my highest voltage is just 12-14 voltage depending on charge ?

[Howard Rush]

believing that al gore is and wack job and believeing in good science and good politices are not neccessilary the same or exclusive.

Looking at the article on dangerous voltages .,.what does that have to do with multiple batteries hooked up in parralle where my highest voltage is just 12-14 voltage depending on charge ?

I just wondered why you would have a sufficiently strong opinion on such a complicated subject that you would express it while requesting advice on how to charge a battery, but you literally spell out the explanation well in your response above.  

I'm not sure what Dave meant by 2) in his second post, but I think his earlier suggestion was to put the batteries in parallel and use diodes to keep them from hurting each other.  With that arrangement, even if the open-circuit solar panel voltage is high, you wouldn't be exposed to a high voltage if you remove one cell at a time, leaving the others hooked up.  I don't know the electrical characteristics of solar cells, but looking some at links from the photovoltaic page on Gary Reysa's excellent Web site, http://www.builditsolar.com/Projects/PV/pv.htm#Basics , it looks like RV solar panel systems come with a controller for charging a 12V RV battery.  That could result in too much current to your smaller batteries on a sunny day or too little current if the controller is a constant-voltage source at, for example, 14.4V, and you wire the charger per the sketch I drew: the diodes will lower the voltage to each battery by .7 volts or so.  If there's plenty of voltage from the solar panel, you may be able to use resistors in series with the diodes to make the charge current come out right.  

 

[Richard Grogan]

Besides using the diodes and balance resistors to prevent backfeeding the solar panels, you could also add a photocell with a relay- to drop(open) the B+ lead from the solar cell panels, and open the path at night...all automatically. On at dawn, off at dusk.

[jim gilmore]

Is all the diods neccessary if I'm using solar panels with a charge controller ?

[Jimmy R. Jacobs]

  To charge batteries, you need 13-14 volts and amps.  My small battery charger is 2 amp trickle charge and 10 amp on high charge.  In the winter I keep 3 RV batteries wired parallel on 2 amp charge, and it works.  You need amperage to charge batteries, not just voltage, but you must have 13-14 volts.

[Larry Cunningham]

I've designed charge controllers for high altitude balloon payloads, and they can be fairly sophisticated, but they are not charging lead-acid batteries. Lead acid batteries are pretty robust and tolerant of charging and discharging - connecting multiple ones in parallel is unlikely to damage them; and as pointed out, 12V lead acid batteries are not really 12V but >13.4V (as I recall). So, what's going to happen? Well charged one(s) will source current to the discharged one(s). But unless there is damage to a battery (say it is dead and shorted), nothing dreadful is likely to happen - eventually you might end up with four similarly charged batteries..

Considering the current levels available from typical solar arrays, four car batteries in parallel aren't going to be harmed in any manner, and the batteries WILL regulate the applied voltage to ~13.4V. (Batteries make great voltage regulators.)

I'd likely use diodes, because diodes are cheap (get a pack of six at Radio Shack for a few bucks) and work very well (they do cost you about .6V forward drop for a silicon diode) and because I Fear No Diode. Series resistors aren't required to protect such batteries, I suppose they might protect the solar cells (which I doubt will be harmed being shorted or heavily loaded in atmosphere <vs vacuum of space> where cooling is not likely any problem).

Under good conditions, sunlight energy amounts to about a kilowatt per square meter. That's a lot, but typical solar cell efficiency is only about 12-20% for commercial ones (newest research cells are now approaching 50% efficiency). A typical 150W commercial solar panel is about a square meter in size, and will produce about 1 kilowatt-hour per day.

Anyway, unless you have a very large solar array (very large!), it's unlikely to generate any very dangerous voltages or currents. But a 12V car battery can turn a ring or watch into a red hot object that will damage your flesh severely - in seconds.

(If you really want to do harm with the sun, a magnifying glass works quite well.)

L.

"Everything goes wrong all at once." -Quantized Revision of Murphy's Law

[Clayton Berry]

I was all prepared to say that 1.5 volts from a starter battery seems a lot safer around a partial gallon of glow fuel than your typical 12 volt motorcycle battery that the RC guys use to run their 'power panels'.  And that a hand crank or a syringe will fill your tank reasonably quickly.

Now that I realize you're searching for gold - can I get you to seek out my first wedding band?  About 40 feet from shore, maybe 6 feet deep.  Lake Manassas, in Virginia.  Was fishing, went to shake my hand to rid myself of slime, and watched it shoot off the ol' finger.  Eastern shore, think.  Reward money is still available.

[john e. holliday]

It doesn't matter  if it's a 1.2 volt nicad or a 12 volt gel cell, it is the spark that causes the explosion.  That is if I remember right.  Did watch a guy put out a lit match in a can of gasolene.   

[Pinecone]

The point was that when you get up above 60 volts DC, you are into an area where you can get some serious consequences.  Even in series, you are up to about 55 volts fully charged.

The problem with parallel setup is not when charging, but when the charger is off.  At that point, the highest voltage battery will try to charge any lower voltage batteries.  And the batteries can ratchet each other down until they are all dead.

[John Witt]

Lead acid cells will (at room temperature) self discharge about 1/2% per day. This is the reason for trickle charging stored lead acid batteries. In addition, the chemistry of these cells makes them like to be stored fully charged. As the lead combines with the sulfur during discharge, lead sulfate is formed. The lead sulfate has two material phases. In the first phase the material is amorphous and the chemical combination is easily reversed by charging. If the battery is left discharged for some time, the amorphous phase changes to a crystalline phase which is not reversible, and your battery is dead.

As stated earlier, the lowest cells will pull the others down to the same voltage, but the chemical self discharge will pull down the whole string of cells until the battery is dead.

Periodically recharge lead acid cells about once a week or get a proper trickle charge on them. This is basically all true for lead acid gel cells as well.

John W

[Larry Cunningham]

As a result of charging, lead-acid batteries produce hydrogen (and oxygen), which is combustible. Under normal conditions (not overcharging) gasses will safely dissipate.

But any device which can release a large amount of stored energy is potentially dangerous. Remember Apple's early problems with "exploding" laptops?  An electrical short can release enough energy to cause a fire or explosion. The more efficient types of batteries are typically the worst about doing dangerous things.

L.

"Never cut what can be untied." -Joseph Joubert

[jim gilmore]

Yup, I know all about batteries and their minor problems. I say minor because they are all simple to avoid.
1- never short a battery or a wire on a car. It will result in big problems as the insulation will met fast and the fire.
2- batteries create hydrogen. make sure any space for batteries is vented well.
avoid wearing rings and placing wrenches where they can come in contact with the batteries.

All these problem have simple solutions.
While 12 volts is insufficent to kill, capicitors can hold enough to do the job nicely. Even if the battery has been disconnnected.

[Peter Ferguson]

So this looks like a good place to ask my question. When I was in scouts I built a 2 tube radio, remember them? It used a 90 vdc dry cell battery(ninety). It cost a fortune and looked like a giant 9v battery with the snap connector at one end. I was always dared by my brother to put my tongue across the smaps like you do with a 9v battery but i wouldn't. I always wondered what kind of jolt I would have gotten from that battery. Anyone here try it?

[jim gilmore]

as the current goes from point a to point be depending where it most likely would put a hole in your tongue.
As a battery it is attempting to go to the second post for a complete circut.
if you were to grab both posts from hand to hand you may not even feel a shock but if you use your tongue and the posts are close say both posts could tough your tongue it wold smart.