Circuit on batteries recharging Battery packs, 2 questions

[prathamesh_d2001]

I am running a . The Circuit needs +12V and -5V supply w.r.t. ground. so the battery packs are arranged in this way as shown in the diagram. there is a switch Put in the common Path to ON/OFF the supply for both Display as well as circuit. I have 2 Problems here :

1. I want to develop a circuit for recharging the batteries all of them but without breaking the existing arrangement. Right now only +12V side can be recharged but not -5V.

2. The batteries are losing their charge very fast. In 2 hours only after charging and even in switched off condition the batteries lose charge and are unable to switch ON the circuit. While I suspect this is due to ON/OFF switch in COM path (Negative Switching), my colleagues suspect that the batteries are made in china and of bad quality. Please help me in understanding this phenomena.

 

[JStuffer]

Re: Recharging Batteries

When the switch is off and the batteries still attached to the circuit, there is still connection to the voltage terminals. It depends on what circuit you are working with, but if there is a current path between ie. the 12V and 6V terminal, it will obviously discharge, even if the ground/Com is disconnected. Look at the circuit to see how it's connected. It would help if you could post the schematic here to give us better insight.

You could also change the single switch to multi-channel switch or something.

Edit:
Just added a drawing of how i mean it. It also includes a simple charging connection. Please note, that if all the 1.5V cells (an assumption) are connected this way, it's 16 cells in series. You probably shouldn't charge them in this configuration, because due their slight differences in capacity, they will soon diverge in charge state and some of them may become forced into overcharge or reverse. In order to recharge, you should remove them and recharge outside, properly.


JS.

 

[prathamesh_d2001]

Recharging Battery packs !!

thank U very much for the Scheme u have suggested..it definitely worked. how should i design a DC -DC converter that will work with variable input (18-30VDC) and give 20VDC at the output.? i think i need to apply boost technology here..any suggestions ?

 

[karesz]

Recharging Battery packs !!

Hi,
Batteries are for limited cycle usable!
Its value is very depend of the special model & handling! :-(
Especially, if you did it not discharged (i.e. a laptop battery) ca. 1x pro month; after some time (can be at 2 years) the battery will be "to old", lost on capacity, as in your case:its to change out....
Btw has your battery surly enough nominal capacity?
K.

 

[JStuffer]

Re: Recharging Battery packs !!

Hi, you should probably look for a buck-boost converter (or boost-buck, supposedly they're different?) or SEPIC topology, as your input voltage varies both below and above your desired output voltage.

Here's what i found:

http://www.onsemi.com/pub/Collateral/AN920-D.PDF
Page 17: step-up/step-down. The MC33063 is a cheap device, but doesn't have the current capability you need. An external transitor is usually added to do the switching.

www.onsemi.com/pub_link/Collateral/MC34163-D.PDF
MC33163 is a more powerful version of the above. See datasheets.

http://cds.linear.com/docs/Datasheet/3780fe.pdf
LT3780 looks like the right thing if you want to make it look "pro". Perhaps a bit too clumsy? It may be unavailable or expensive, though.

www.national.com/ds/LM/LM5118.pdf
LM5118 looks promising, easier to work with.

http://cds.linear.com/docs/Datasheet/4607fa.pdf
This thing has a ridiculous package, SMD LGA, no way to hand-solder.

I definitely like the LM5118 - see if you can find it. Also the MC33163 could do a good job.

Do some searching for the keywords "buck-boost" and similar. See if you find something more.

Last note: I'm not sure from what you wrote, whether you'll be able to charge the batteries separately or if you're planning to charge them chained as the're now. But bear in mind that if you keep them serialized and charge, you'd be asking for a disaster after several cycles. For charging, try to split them into shorter chains, even if it involves a lot of reconnecting/switching when you get to charge them.

Good luck.
JS

 

[prathamesh_d2001]

Re: Recharging Battery packs !!

Thanks for the help, all of u. I will work on those schemes too. by the way, the plan has been changed. now instead of +12V and -5V, I am going to use +5V and -5V. also the battery pack i was using earlier was hopeless as it had lots of Mechanical problems and Battery Quality Issues. so I am going to use 6V single Rechargeable Battery. i.e. circuit will need 2 batteries of 6V arranged similarly. now that i will need only buck converter of 12-13V to recharge them. I am reading earlier posts of buck converter/chargers. unfortunately size is the problem, cannot have big circuit. need somthn small enough to fit with the rest of the PCBs in a small box.

 

[JStuffer]

Re: Recharging Battery packs !!

Good. Try to find out what type the batteries are (ie. two lead-acid packs of 3 cells or two lithium-based packs of 2 cells or two nickel-based packs of 4 cells).
A circuit that uses up little space is one with LM2576, but you'll probably find better suiting devices. It depends on the battery chemistry and capacity / rated charging current. Please share those parameters, so you can get better feedback.
www.national.com/ds/LM/LM2576.pdf
- but this circuit still may have to be modified for good charging control.

JS

 

[prathamesh_d2001]

Re: Circuit on batteries recharging Battery packs, 2 questio

finally I have created a Solar PV panel tester which is actually nothing but an Electronic CV Load. I put only +5V supply and inverted it thru TPS60400 which at output gives -5V. Now all I need is 4 Batteries of 1.2V. and batteries i am using are NiMH. I have provided charging system thru adapter of 6V , but need to built a circuit of 6V buck which will charge the batteries whenever the Tester is connected to PV panel. Thanks again for the links of Buck Converter..