solar panel + battery to power electronics project

[littlepigboy5]

I am making a little recording light so that when i flip a switch attatched to an arduino in my room, it will send a signal to an rf transmitter, which will transmit that signal to the receiver which will be above my door.  then that receiver will send a signal to a transistor which will connect a red led to a battery to turn it on.  I have most of the design done, but I am stuck with the part that will be above my door, the receiver transister and led.  I don't want to have to plug it in and have an ugly wire running down my door.  So i thought to use a solar panel that works with indoor lighting, but I want it to work when the lights are off so the solar panel will charge a battery.  I don't know what kind of battery i should use.  it will only be powering a receiver and led.  I am not great with ohms law and figuring out how much voltage or amperage i need, so does anybody know how I can find out what kind of battery I need, and if there are any solar panel recommendations you can make that would be great.

Thanks

[Enderman]

all that really matters is that you get the voltage right

as long ass its a decent sized battery the amps dont matter, more is better

find the right voltage nimh cell for the led and receiver, and get a solar panel which outputs the same or slightly more voltage than the battery

i would recommend at least 1-2Ah for the battery

[littlepigboy5]

Just now, Enderman said:

all that really matters is that you get the voltage right

as long ass its a decent sized battery the amps dont matter, more is better

find the right voltage nimh cell for the led and receiver, and get a solar panel which outputs the same or slightly more voltage than the battery

i would recommend at least 1-2Ah for the battery

Ok, I think I just figured a lot out on my own while searching around.  I need a 5v battery for the receiver, and that will also go to transister and then to my led, which will be fine.  Does the amperage of the solar panel matter?  because the battery needs to be able to supply power with the lights off, for longer than a few seconds lol, so the solar panel needs to be able to charge the battery at a reasonable pace.

[Enderman]

5 minutes ago, littlepigboy5 said:

Ok, I think I just figured a lot out on my own while searching around.  I need a 5v battery for the receiver, and that will also go to transister and then to my led, which will be fine.  Does the amperage of the solar panel matter?  because the battery needs to be able to supply power with the lights off, for longer than a few seconds lol, so the solar panel needs to be able to charge the battery at a reasonable pace.

more is better

but dont go over 1C charge rate

so the solar panel should output the same or less amps than your battery has amp-hours

[littlepigboy5]

Just now, Enderman said:

more is better

but dont go over 1C charge rate

so the solar panel should output the same or less amps than your battery has amp-hours

what is 1C?  or I guess what unit is C?  and I am looking on ebay and I can only find nimh chargers, no batteries, could you link me to one, or let me know where I can find one?

[Enderman]

1 minute ago, littlepigboy5 said:

what is 1C?  or I guess what unit is C?  and I am looking on ebay and I can only find nimh chargers, no batteries, could you link me to one, or let me know where I can find one?

c = charge rate/discharge rate

if you have a 2000mAh battery 1C = 2 amps

50C = 100 amps

 

you want to charge nimh batteries at no more than 1C

[littlepigboy5]

1 hour ago, Enderman said:

c = charge rate/discharge rate

if you have a 2000mAh battery 1C = 2 amps

50C = 100 amps

 

you want to charge nimh batteries at no more than 1C

I'm not finding any nimh batteries on ebay, just nimh chargers, where should i look for those?

[Enderman]

2 hours ago, littlepigboy5 said:

I'm not finding any nimh batteries on ebay, just nimh chargers, where should i look for those?

there should be tons...

a lot of rechargeable batteries are nimh

stuff like these http://www.ebay.com/gds/Top-5-NiMH-Rechargeable-Batteries-/10000000177747424/g.html

you can also find C size battery packs which store more mah

[vanished]

3 hours ago, littlepigboy5 said:

I'm not finding any nimh batteries on ebay, just nimh chargers, where should i look for those?

They're the most common type.  If it doesn't say it is probably NiMH (but make sure though)

[DragonTamer1]

Not sure what kind of convenience stores you have in your area so I figured that Walmart would be a good place to look.

 

http://www.walmart.com/search/?query=rechargable+batteries

[littlepigboy5]

9 hours ago, Enderman said:

there should be tons...

a lot of rechargeable batteries are nimh

stuff like these http://www.ebay.com/gds/Top-5-NiMH-Rechargeable-Batteries-/10000000177747424/g.html

you can also find C size battery packs which store more mah

ok, I am going to put 4 aaa nimh batteries in series for ~4aH , but that would mean i need a 6v(1 more volt than my receiver operating voltage) 4a(1C or charge cycle) solar panel, which is 24 watts, which are way too expensive.  COuld I get a way with a few of these in a series? http://www.ebay.com/itm/Mini-6V-1W-Solar-Power-Panel-DIY-For-Cell-Phone-Toys-Chargers-Portable-/201503135437?hash=item2eea85d6cd:g:gA4AAOSwaA5WlyZk .  Also, how would I connect the solar panels to the batteries to charge them and the batteries to my circuit because the batteries only have 1 positive and 1 negative terminal

[Enderman]

4 hours ago, littlepigboy5 said:

ok, I am going to put 4 aaa nimh batteries in series for ~4aH , but that would mean i need a 6v(1 more volt than my receiver operating voltage) 4a(1C or charge cycle) solar panel, which is 24 watts, which are way too expensive.  COuld I get a way with a few of these in a series? http://www.ebay.com/itm/Mini-6V-1W-Solar-Power-Panel-DIY-For-Cell-Phone-Toys-Chargers-Portable-/201503135437?hash=item2eea85d6cd:g:gA4AAOSwaA5WlyZk .  Also, how would I connect the solar panels to the batteries to charge them and the batteries to my circuit because the batteries only have 1 positive and 1 negative terminal

series will increase the voltage not Ah

[vanished]

3 hours ago, Enderman said:

series will increase the voltage not Ah

Wouldn't the total capacity (Ah) increase regardless of configuration?  I mean, you had 2 Ah (just for example) before, and now you have 4 batteries so 4 * 2 = 8 Ah... no?

Putting them in series will increase the voltage and putting them in parallel will increase the current you can safely draw, but I can't escape thinking that capacity would increase regardless.

[littlepigboy5]

3 hours ago, Enderman said:

series will increase the voltage not Ah

then parallel

[vanished]

Just now, littlepigboy5 said:

then parallel

then your voltage is limited to the voltage of 1 battery.  Is that enough?

[littlepigboy5]

23 minutes ago, Ryan_Vickers said:

Wouldn't the total capacity (Ah) increase regardless of configuration?  I mean, you had 2 Ah (just for example) before, and now you have 4 batteries so 4 * 2 = 8 Ah... no?

Putting them in series will increase the voltage and putting them in parallel will increase the current you can safely draw, but I can't escape thinking that capacity would increase regardless.

yeah

 

3 hours ago, Enderman said:

series will increase the voltage not Ah

Do either of you have an idea of how I would wire this, our would I just put the batteries in parallel and have the solar panel connectd to one end and the circuit to the other.

[Enderman]

2 hours ago, Ryan_Vickers said:

Wouldn't the total capacity (Ah) increase regardless of configuration?  I mean, you had 2 Ah (just for example) before, and now you have 4 batteries so 4 * 2 = 8 Ah... no?

Putting them in series will increase the voltage and putting them in parallel will increase the current you can safely draw, but I can't escape thinking that capacity would increase regardless.

Wh=/=Ah

so in parallel you increase the current but not the voltage

in series you increase the voltage and not the current

having multiple batteries will increase the Wh but not the Ah because Ah is how many hours you can continuously draw 1 amp from it, regardless of the voltage

 

two 1v 1Ah batteries in series would have double the voltage but only 1x the amperage, so for 1 hour they would only provide 1 amp and 2 volts

 

in parallel they would last two hours because they can provide 2 amps and 1 volt

 

overall they provide the same Wh because W=A*V but in parallel they last twice as long due to less voltage output

[littlepigboy5]

27 minutes ago, Enderman said:

Wh=/=Ah

so in parallel you increase the current but not the voltage

in series you increase the voltage and not the current

having multiple batteries will increase the Wh but not the Ah because Ah is how many hours you can continuously draw 1 amp from it, regardless of the voltage

 

two 1v 1Ah batteries in series would have double the voltage but only 1x the amperage, so for 1 hour they would only provide 1 amp and 2 volts

 

in parallel they would last two hours because they can provide 2 amps and 1 volt

 

overall they provide the same Wh because W=A*V but in parallel they last twice as long due to less voltage output

OK, I think I understand.  so in that case 1 AAA battery is about .57 amps, so four of them in parallel would be about 2 amps, but the same amount of watt hours because the wattage is the same, but in parallel they will last longer.  aside from this, where do i hook up the solar panel?

[Enderman]

59 minutes ago, littlepigboy5 said:

OK, I think I understand.  so in that case 1 AAA battery is about .57 amps, so four of them in parallel would be about 2 amps, but the same amount of watt hours because the wattage is the same, but in parallel they will last longer.  aside from this, where do i hook up the solar panel?

positive end of the solar panel goes to the positive end of the battery

negative to negative

[vanished]

2 hours ago, Enderman said:

Wh=/=Ah

[...]

having multiple batteries will increase the Wh but not the Ah because Ah is how many hours you can continuously draw 1 amp from it, regardless of the voltage

I'll admit I thought about this for an embarrassingly long time before I realized you are right; the Wh (which is what I was thinking about in my initial comment for some reason) will sum regardless of configuration but Ah only add in parallel, since in parallel, the 1 amp of load is spread across all batteries but in series each battery in the stack would have to supply the full 1 amp, no different than if the 1 amp was drawn from a single battery.

[Enderman]

5 minutes ago, Ryan_Vickers said:

I'll admit I thought about this for an embarrassingly long time before I realized you are right; the Wh (which is what I was thinking about in my initial comment for some reason) will sum regardless of configuration but Ah only add in parallel, since in parallel, the 1 amp of load is spread across all batteries but in series each battery in the stack would have to supply the full 1 amp, no different than if the 1 amp was drawn from a single battery.

[littlepigboy5]

23 hours ago, Enderman said:

positive end of the solar panel goes to the positive end of the battery

negative to negative

Then how does that hook up to my circuit, the batteries only have 1 positive and 1 negative terminal

[vanished]

1 minute ago, littlepigboy5 said:

Then how does that hook up to my circuit, the batteries only have 1 positive and 1 negative terminal

Same way it would have without the solar panel, except now there is a solar panel in parallel with the battery to provide extra power and charging when possible.

[littlepigboy5]

2 minutes ago, Ryan_Vickers said:

Same way it would have without the solar panel, except now there is a solar panel in parallel with the battery to provide extra power and charging when possible.

ok I understand.  One more thing, with 4 AAA nimh batteries, what wattage of a 6v solar panel should i get?

[vanished]

19 minutes ago, littlepigboy5 said:

ok I understand.  One more thing, with 4 AAA nimh batteries, what wattage of a 6v solar panel should i get?

Basically you need enough battery capacity to last as long as the longest expected dark period (I assume you've worked out that the 4 AAA is enough) plus (imo) a little extra since over time the batteries won't quite hold a complete charge any more.  Also you don't want to cut it too close do you?

 

Once you've got that sorted out, you need a panel that will deliver enough power during the times that it is bright to be able to run the device and charge the batteries fully from near dead in whatever period of time it is bright for.

 

I'm not sure about your specific batteries but if we assume each one is about 1.5 Wh, the four together will be 6 Wh.  Lets say the lights will be on for 8 hours.  You need to be able to provide 6 Wh in 8 hours, or in other terms, 6 Wh / 8 h = 0.75 W.

 

So a 0.75 W panel should be able to charge the batteries in 8 hours (if your durations or capacities vary, adjust this as necessary).

 

Note that you'll want to make sure whatever option you pick does not exceed the "C" charge rate you worked out earlier