Battery charging in parallel

Thread Starter

RodneyB

Joined Apr 28, 2012
697
Hi,

That's a very good idea, but only if the resistances are similar and if the added resistances dont have to be too high in value.

The best way however is to use a higher voltage for the higher resistance battery, and see if that brings the resistance down (it may). If so then the problem may get better and you wont have to do this again for a while.

If not, then the best way is to use a separate voltage for each battery. If you need a higher voltage for the 2nd battery you can use a small boost circuit. Yes that makes things a little more complicated, but batteries are devices that are not as simple as they appear to be.[/QUO

Can you direct me to a circuit for a boost circuit for a 12 volt 7Ah ela battery
 

MrAl

Joined Jun 17, 2014
7,191
Hi,

I think you mixed your reply up with the quote :)

Your question repeated here for clarity was:
"Can you direct me to a circuit for a boost circuit for a 12 volt 7Ahr ELA battery?"

I will look around. You really want a circuit or a ready made board ?
 

Thread Starter

RodneyB

Joined Apr 28, 2012
697
Hi,

I think you mixed your reply up with the quote :)

Your question repeated here for clarity was:
"Can you direct me to a circuit for a boost circuit for a 12 volt 7Ahr ELA battery?"

I will look around. You really want a circuit or a ready made board ?

Hi I would like the circuit, its really hard for me to get boards that are already made here.
 

Thread Starter

RodneyB

Joined Apr 28, 2012
697
Nobody in Zimbabwe makes circuit boards? Sounds like it's time to make your own.
Sorry i do make my own pcb what i meant it's impossible to buy anything a board completed from ebay or similar. Therefore i like circuit diagrams so i build my own. Often a lot more expensive however i have it

Sorry for confusion created
 

MrAl

Joined Jun 17, 2014
7,191
Hello again,

Because of your location, i can not be sure what kind of parts you can get so maybe you can show a few typical types of parts you can actually get.

If you can order from Amazon, you can get ready made boards.

If you can order from a supply house that carries TI products, maybe the LM3478 controller could be a good starting point. You can look on the Texas Instruments site for more info on that chip and see if it seems plausible. It will require a good external MOSFET for the power switching.

If you can not order any of these parts it will be more difficult using discrete parts like just transistors, but if you can use op amps like the LM358 that will help too.
 

Thread Starter

RodneyB

Joined Apr 28, 2012
697
Hello again,

Because of your location, i can not be sure what kind of parts you can get so maybe you can show a few typical types of parts you can actually get.

If you can order from Amazon, you can get ready made boards.

If you can order from a supply house that carries TI products, maybe the LM3478 controller could be a good starting point. You can look on the Texas Instruments site for more info on that chip and see if it seems plausible. It will require a good external MOSFET for the power switching.

If you can not order any of these parts it will be more difficult using discrete parts like just transistors, but if you can use op amps like the LM358 that will help too.
I can get it from RS components. In south Africa. Is it only a surface mount component
 

MrAl

Joined Jun 17, 2014
7,191
Hi,

Well i am not sure what you are saying here, but if you want to look at the circuit you can look up the part on the TI site and see how they recommend using it. If that seems to suit you that may be the way to go. I hesitate to give you a custom design because boost converters are a little more tricky than say buck converters. Which reminds me, if you had a higher voltage to start with already that would be even better because then a buck or linear regular could be used and that would be simpler.

Assuming the boost for now, it would be good for you to try to use a circuit that is known to work already, like a reference design from TI that goes with their part number.

I assume you can work with surface mount parts, but if not, we can look at another older chip which is also a controller chip. It's been around for a long time and it (or similar) is actually in many PC computer power supplies to this day. The TL497A might work here as they show a boost configuration on the data sheet. Comes in a DIP package i believe. Hopefully it is still made today.
 

Thread Starter

RodneyB

Joined Apr 28, 2012
697
Hi,

Well i am not sure what you are saying here, but if you want to look at the circuit you can look up the part on the TI site and see how they recommend using it. If that seems to suit you that may be the way to go. I hesitate to give you a custom design because boost converters are a little more tricky than say buck converters. Which reminds me, if you had a higher voltage to start with already that would be even better because then a buck or linear regular could be used and that would be simpler.

Assuming the boost for now, it would be good for you to try to use a circuit that is known to work already, like a reference design from TI that goes with their part number.

I assume you can work with surface mount parts, but if not, we can look at another older chip which is also a controller chip. It's been around for a long time and it (or similar) is actually in many PC computer power supplies to this day. The TL497A might work here as they show a boost configuration on the data sheet. Comes in a DIP package i believe. Hopefully it is still made today.
Hi

I can work with surface mount. I will organise to import the components. In the meantime i will do the PCB layout.

I find learning using thm components a lot easier but quite happy to try this
 
I don't understand why a battery I have in parallel with another battery does not charge.

The bigger of the batteries is connected to the charger. The smaller battery a 7Ah battery it is used as back up when the big battery is not connected.

The small battery goes flat I then connect it to the big battery, the voltage goes up slightly but not to the same voltage as the big battery, I would really like to understand why
I am answering by assuming that we are talking about Lead Acid (LA) Batteries, the type was never mentioned! That could make a serious difference!!!

Never charge two batteries in parallel (or in series either! Though a battery is a series of "cells" and cannot usually be charged any other way.), even if always used together, bought together, same manufacturer etc etc....

Also, never forget that each "cell" is an individual, one cell in a battery will be, even from new, the weakest. Another will be the strongest. You must try to use and charge a battery BETWEEN the "needs" of both of these two cells.....difficult. This is true of any battery type, not just LA.

The weakest cell (or battery in a multi battery situation!) will be charged first. While the other cells are still being charged, it will be overcharged, making it weaker still!!

The weakest cell (or battery in a multi battery situation!) will be discharged first. While the other cells are still supplying power, this cell will be reverse polarised, making it weaker still!!

Even if you have say a 36 volt Golf cart, with probably 3 x 12 volt batteries, these are often charged in series, but if 3 x 12 volt chargers are used instead, with voltage limited charging, then all three batteries will achieve their best possible life, as long as they are not "over" discharged in use.

I also prefer not to charge above about 13.8 volts, then no gassing, but depending upon battery, type, age and manufacturer, only around 70% of capacity will be achieved. Therefore I tend to buy a larger battery, with at least 30% more capacity than I need. But do not use it!!

Never use a charger that has no setting for charge to STOP at a particular point (voltage) you select, it may get a higher percentage of charge in the battery, but dramatically lowers efficiency, causes gassing (water loss), and reduces life span. Once you charge above 70%, both of these things are happening.

Cheap car chargers, even ones with a low charge level (current), left on a battery far too long, are often the reason for early demise of a LA Battery. Adding circuitry to one of these to control the charge better is a cheap alternative nowadays. Also, adding full wave rectification, will make better usage of the transformer in such a unit as they generally have only half wave rectification for some unknown, obtuse reason!! A part that is worth only a few cents in large numbers....

Chargers with a "float" feature are a big risk for any battery, as unless VERY sophisticated electronics are used, the float voltage will almost never be right. It changes with the temperature, age, size, type of LA Battery....if it was always right with no electronics, go any buy a lottery ticket, I guarantee you will win!!!

Float must be a charge level, that maintains the voltage of the battery, never increasing or decreasing.....I also believe, that it "makes a battery lazy!" I have experience, but no proff....

Charging too fast will also cause gassing and battery deterioration. C/10 (batter CAPACITY divided by 10. e.g. a 100 amp battery only charge at max of 10 amps, lower is better!) is a max current!!

On a big heavy duty (high current) battery charger, adding some heavy duty ceramic resistors on the DC low voltage side, will reduce the charge current to a safe level....

With careful selection of resistors, any small battery can still be safely charged. Look for ones with values between say 12 to 40 Ohms will prove useful. although such a resistor wastes power.

Therefore one heavy duty charger can then be used for different sized batteries. But do learn your I2R, to make sure that the resistors will not overheat. More of them in parallel can be used to achieve cooler running! Learn Ohm's Law!!

Adding a voltmeter to a simple charger (assuming a current meter is already fitted!), will add dramatically to your knowledge and safety. Even a cheap multimeter could be used on say DC volts 20 volt range, once it has been carefully checked against a known good meter to show that in the range 8 - 20 volts, it is accurate enough. Some aren't!!

If you use external ceramic resistors, remember the voltmeter MUST be across the battery, NOT the charger output!! Important!!

I hope this helps.

I have read a lot of the posts here, some are wrong, some are downright dangerous, so be very careful!!
 

hp1729

Joined Nov 23, 2015
2,304
I am answering by assuming that we are talking about Lead Acid (LA) Batteries, the type was never mentioned! That could make a serious difference!!!

Never charge two batteries in parallel (or in series either! Though a battery is a series of "cells" and cannot usually be charged any other way.), even if always used together, bought together, same manufacturer etc etc....

Also, never forget that each "cell" is an individual, one cell in a battery will be, even from new, the weakest. Another will be the strongest. You must try to use and charge a battery BETWEEN the "needs" of both of these two cells.....difficult. This is true of any battery type, not just LA.

The weakest cell (or battery in a multi battery situation!) will be charged first. While the other cells are still being charged, it will be overcharged, making it weaker still!!

The weakest cell (or battery in a multi battery situation!) will be discharged first. While the other cells are still supplying power, this cell will be reverse polarised, making it weaker still!!

Even if you have say a 36 volt Golf cart, with probably 3 x 12 volt batteries, these are often charged in series, but if 3 x 12 volt chargers are used instead, with voltage limited charging, then all three batteries will achieve their best possible life, as long as they are not "over" discharged in use.

I also prefer not to charge above about 13.8 volts, then no gassing, but depending upon battery, type, age and manufacturer, only around 70% of capacity will be achieved. Therefore I tend to buy a larger battery, with at least 30% more capacity than I need. But do not use it!!

Never use a charger that has no setting for charge to STOP at a particular point (voltage) you select, it may get a higher percentage of charge in the battery, but dramatically lowers efficiency, causes gassing (water loss), and reduces life span. Once you charge above 70%, both of these things are happening.

Cheap car chargers, even ones with a low charge level (current), left on a battery far too long, are often the reason for early demise of a LA Battery. Adding circuitry to one of these to control the charge better is a cheap alternative nowadays. Also, adding full wave rectification, will make better usage of the transformer in such a unit as they generally have only half wave rectification for some unknown, obtuse reason!! A part that is worth only a few cents in large numbers....

Chargers with a "float" feature are a big risk for any battery, as unless VERY sophisticated electronics are used, the float voltage will almost never be right. It changes with the temperature, age, size, type of LA Battery....if it was always right with no electronics, go any buy a lottery ticket, I guarantee you will win!!!

Float must be a charge level, that maintains the voltage of the battery, never increasing or decreasing.....I also believe, that it "makes a battery lazy!" I have experience, but no proff....

Charging too fast will also cause gassing and battery deterioration. C/10 (batter CAPACITY divided by 10. e.g. a 100 amp battery only charge at max of 10 amps, lower is better!) is a max current!!

On a big heavy duty (high current) battery charger, adding some heavy duty ceramic resistors on the DC low voltage side, will reduce the charge current to a safe level....

With careful selection of resistors, any small battery can still be safely charged. Look for ones with values between say 12 to 40 Ohms will prove useful. although such a resistor wastes power.

Therefore one heavy duty charger can then be used for different sized batteries. But do learn your I2R, to make sure that the resistors will not overheat. More of them in parallel can be used to achieve cooler running! Learn Ohm's Law!!

Adding a voltmeter to a simple charger (assuming a current meter is already fitted!), will add dramatically to your knowledge and safety. Even a cheap multimeter could be used on say DC volts 20 volt range, once it has been carefully checked against a known good meter to show that in the range 8 - 20 volts, it is accurate enough. Some aren't!!

If you use external ceramic resistors, remember the voltmeter MUST be across the battery, NOT the charger output!! Important!!

I hope this helps.

I have read a lot of the posts here, some are wrong, some are downright dangerous, so be very careful!!
It certainly does help. Thanks much.
 
In this case, I would take a note from the trucking induatry. When you have multiple pack batteries, separate them and charge them individually. Does not matter series or parallel, weak batteries won't charge properly. Little story.
Four guys digging a hole and one gets tired. He goes home but hole still needs to be dug by deadline. Three guys work harder to get it done. Boss sends in new guy to help. New guy does most of work because he's fresh and othe three slack off. New guy gets tired faster than normal.
Moral of story:eek:ne bad battery in pack, replace all. I work in this industry and have seen all the battery ideas there are. The guys here have not lead you astray. Separate, charge and test. Replace as necessary.
Are u a truck mechanic?
 

JMW

Joined Nov 21, 2011
123
Is there no circuit i can build to be able to assist the charging. If the charger is charging at 13.8 volts and the small battery has dropped to 10.6 volts what i don't understand is why the smaller battery won't charge to the 13.8 volts
Yes there is, one such device is called an "Echo Charger" by Heart. As another fellow stated the 10.6 volt battery has a defective cell, probably can't be salvaged
 

bwilliams60

Joined Nov 18, 2012
1,261
Are u a truck mechanic?
I am a certified Truck and Coach technician, certified Automotive technician and a College Professor of both with about 35 years in the trade. Most of my time has been spent working on the electrical and electronic side of vehicles having owned an Auto Electric business for many years. I have spent a lot of time working with batteries and charging/starting systems. Electronics is a hobby which I just got back into over the last year or so.Curious about the question??
 

JMW

Joined Nov 21, 2011
123
Boats will typically have a "house" bank that is used to run lights, fans, etc w/o the need for the generator. I have worked on boats with 6 8D deep cycle batteries. They are always charged in parallel. Occasionally there will be 24 or 48VDC systems using series parallel combos. These systems usually supply an inverter. Multi-bank chargers are available that will accomodate different types batteries. The manufacturer always states the batteries should be replaced as a unit, e.g. each bank should be replaced in its entirety. The Heart Echo charger I mentioned above/below can be used to charge a different type of cell from the "house" bank. It automatically switches on/off depending upon the state of charge of both the batteries. Yes, you can make your own, the factors you must consider are, type of battery, and the manufactures recommended charging rates. Leaving batteries in a partially discharged state may lead to sulfation of the plates, permanently reducing the capacity of the battery. Battery isolators, while nice, prevent the charger from "seeing" the battery/bank on the other side of the isolator. If you go this route be aware of the limitation and charge accordingly. Newer isolators use Schotkey diodes, minimizing the voltage drop.
Most of what I have posted is distilled from the "Battery University" a fine site with more info than most will ever need.
 
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