Switch between voltage sources automatically and charge battery

tcmtech

Joined Nov 4, 2013
2,867
What is unclear is how you plan to charge the battery and not have the charger power your circuit.
Simple voltage level logic. Which ever voltage source is higher will power the load.

If the supply voltage is lower than the battery voltage then the battery supplies power just like it supposed to.

I don't see the need to overly complicate the logic any further than that.

As for the charger unit drawing power when its supply is off I have doubts that it would be designed that way being if it could then its possible for a charger to completely drain a battery down to the point of doing damage if it ever lost its input power for long enough while still having the battery connected.

At worse if it did a simple low forward drop germanium power diode will solve that problem without drastically affecting the batteries charging process and capacity.
 

Thread Starter

Rtlane

Joined Dec 27, 2015
27
This is what I think you're describing:
View attachment 97423
What is unclear is how you plan to charge the battery and not have the charger power your circuit.

When the charger isn't being powered, it might appear as no load to the battery; but, then again, it might not.
What if I add another diode so the battery can't see it as a load.
upload_2015-12-28_15-25-7.png
 

dl324

Joined Mar 30, 2015
16,839
By the way, what are you using to draw your schematics?
I use the freeware version of Eagle. Instead of screen shots, I print to PDF and take "snap shots" from that in my PDF viewer. That gets rid of the annoying color coding on the drawing which conveys no useful information.
 

dl324

Joined Mar 30, 2015
16,839
What if I add another diode so the battery can't see it as a load.
If you connect something like this:
upload_2015-12-28_14-5-20.png
You only need 2 diodes. You still need to work out what to do when you're charging the battery. Will you also have PSU on? Or will you attempt to charge the battery and power the circuit simultaneously?

You stated that the charger was rated for 800mA. Will a 1.5A, or larger, load damage it? Will the battery ever charge? Will the circuit tolerate charging voltage minus a diode drop?

If you want simple, you can remove the battery from the circuit to recharge.

Personally, I would have put a switch in the box with a "?". But a P MOSFET wouldn't work well because the PSU voltage is lower than the charging voltage, and I was trying to avoid resorting a solid state relay.
 

ebeowulf17

Joined Aug 12, 2014
3,307
If you connect something like this:
View attachment 97431
You only need 2 diodes. You still need to work out what to do when you're charging the battery. Will you also have PSU on? Or will you attempt to charge the battery and power the circuit simultaneously?

You stated that the charger was rated for 800mA. Will a 1.5A, or larger, load damage it? Will the battery ever charge? Will the circuit tolerate charging voltage minus a diode drop?

If you want simple, you can remove the battery from the circuit to recharge.

Personally, I would have put a switch in the box with a "?". But a P MOSFET wouldn't work well because the PSU voltage is lower than the charging voltage, and I was trying to avoid resorting a solid state relay.
You keep bringing up a hypothetical scenario in which the psu is disconnected, but the charger is charging the battery. The charger gets power from the psu. It's not powered from some other phantom source not shown in these schematics. So the charger couldn't possibly be charging the battery when the psu is disconnected, right? Why are you worried about what appears to be an impossible situation? Am I missing something here?
 

dl324

Joined Mar 30, 2015
16,839
So the charger couldn't possibly be charging the battery when the psu is disconnected, right? Why are you worried about what appears to be an impossible situation? Am I missing something here?
You are making assumptions that are not foregone conclusions. The OP has not given sufficient detail to rule anything out.
 

Thread Starter

Rtlane

Joined Dec 27, 2015
27
You are making assumptions that are not foregone conclusions. The OP has not given sufficient detail to rule anything out.
I mentioned before that the charger is not plugged in the wall along with the psu. It is ONLY powered by the wall psu.
 

dl324

Joined Mar 30, 2015
16,839
I mentioned before that the charger is not plugged in the wall along with the psu. It is ONLY powered by the wall psu.
Yes, but you were not clear on whether the PSU would ever be used to power both simultaneously or the charger alone. That's why I had to ask so many clarifying questions.
 

Thread Starter

Rtlane

Joined Dec 27, 2015
27
If the wall psu is plugged in i want:
-The wall psu to power the charger so the battery will charge and i dot NOT want the battery to power the circuit
-The wall psu to power the circuit

If the wall psu is Not plugged in i want:
-the battery to supply power to the circuit and thats it.
.
I said the above earlier, sorry if it wasn't enough detail.
Yes, but you were not clear on whether the PSU would ever be used to power both simultaneously or the charger alone. That's why I had to ask so many clarifying questions.
 

tcmtech

Joined Nov 4, 2013
2,867
Yes, but you were not clear on whether the PSU would ever be used to power both simultaneously or the charger alone. That's why I had to ask so many clarifying questions.
I don't see where the confusion could be from. The power supplies output voltage (14 VDC) is higher than the battery chargers output can go (12.6 max) thus it will be the supply for the device at the end regardless of whether or not the battery is charging.

I'm not sure how that concept can be so confusing or have so much read into it. :rolleyes:
 

Thread Starter

Rtlane

Joined Dec 27, 2015
27
I don't see where the confusion could be from. The power supplies output voltage (14 VDC) is higher than the battery chargers output can go (12.6 max) thus it will be the supply for the device at the end regardless of whether or not the battery is charging.

I'm not sure how that concept can be so confusing or have so much read into it. :rolleyes:
LOL
 

Thread Starter

Rtlane

Joined Dec 27, 2015
27
I don't see where the confusion could be from. The power supplies output voltage (14 VDC) is higher than the battery chargers output can go (12.6 max) thus it will be the supply for the device at the end regardless of whether or not the battery is charging.

I'm not sure how that concept can be so confusing or have so much read into it. :rolleyes:
Same though process I had, but Im still learning.
 

ebeowulf17

Joined Aug 12, 2014
3,307
How can 3 diodes in parallel with 1 be considered anything other than a mistake?
Since there are different components connected at the junctions of those three diodes, it seems like they could all serve useful purposes. I don't see an obvious problem here.

I'm still pretty new at all this, and I welcome learning opportunities. If this diode arrangement is problematic, can you explain why? Can you give an example of a situation in which it would do something undesirable?
 

Thread Starter

Rtlane

Joined Dec 27, 2015
27
Im going to try this circuit. I dont see any reason why it shouldn't work, but then again we'll find out.

image_Rtlane.jpeg

Mods Note:
Rtlane:
The files size that you attached were too big for you circuit, I was compressed them to the normal size, they are from about 1.2 MB compressed to about 36KB, next time before you upload the files, please compress the photos to 800x600 or 640x480, if necessary then you can compress to 1024x768, almost the photos using 800x600 image is enough.

Too much file size will affecting the connecting speed of members to get into the forums and to see the circuit, thanks for your understanding and cooperation.
 

Thread Starter

Rtlane

Joined Dec 27, 2015
27
Also if I use a 3 pin dc jack, theres no chance of the battery powering anything when the wall psu is plugged in and It wouldnt matter if the wall psu and battery is same voltage cause the battery would be disconnected when the wall psu is plugged in.
 

Attachments

ebeowulf17

Joined Aug 12, 2014
3,307
Im going to try this circuit. I dont see any reason why it shouldn't work, but then again we'll find out.

View attachment 97498

Mods Note:
Rtlane:
The files size that you attached were too big for you circuit, I was compressed them to the normal size, they are from about 1.2 MB compressed to about 36KB, next time before you upload the files, please compress the photos to 800x600 or 640x480, if necessary then you can compress to 1024x768, almost the photos using 800x600 image is enough.

Too much file size will affecting the connecting speed of members to get into the forums and to see the circuit, thanks for your understanding and cooperation.
Looks good to me. Let us know how it works out!
 
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