# For you inventors!

Discussion in 'Power Electronics' started by jkimbro01, Mar 10, 2019.

1. ### jkimbro01

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Mar 10, 2019
I'd like to make an IP cam battery powered. (or at least see if it's feasible).
It currently is powered by a 5v power supply. Info on it says 5vlts @ 1.5a.
I don't mind changing the battery(s) once a month or so,,,of course longer the better but how big of a battery am I looking at? Or how many? (ish). And I'm assuming it would need to be a 6v battery so nothing else is in the burning power....? Thanks!

2. ### BobK

7,671
1,681
Jan 5, 2010
That is 7.5 Watt hours. A standard car battery is about 45 Amp Hours x 12V = 540 Watt Hours. So a car battery would run it for about 72 hours, or 3 days. 10 car batteries should do it! Oh, wait, you would have to convert down from 12V to 5V and that would be about 80% efficient, so you better get 12 car batteries.

Bob

3. ### jkimbro01

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Mar 10, 2019
hahaha,,, ya,, that's what I was afraid of! Thanks!

4. ### Harald KappModeratorModerator

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Nov 17, 2011
Is that the info on the camera's rating label or on the power supply?
If it is on the camera, the go buy 12 car batteries (just joking).
If it is on the power supply, it only means that the power supply is able to deliver 1.5 A. It does by no means mena that the camera draws that much current. You nead the real current drawn by the camera to repeat Bob's calculation in a realistic scenario.

5. ### jkimbro01

3
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Mar 10, 2019
It's the info on the back of the camera, (Dlink DCS-935L),, but sure seems to me like that's a lot of juice to run such a little piece of electronics! It's not like it's a pan & tilt. <copied from the manual>
However, in the manual I just found an entry that says:
POWER CONSUMPTION • 3.5 watts maximum ± 5%
which my handy dandy calculator says is about .6 amps(ish).
So how many car batteries am I down to now? (LOVE the answer to be less than one! haha)

6. ### BobK

7,671
1,681
Jan 5, 2010
12 x 0.6 / 1.5 = 4.8 car batteries. But do not despair, 3.5W is the max, the average current could be less.

Bob

7. ### dave9

845
206
Mar 5, 2017
If the camera is not always streaming the power consumption will be markedly less. If the camera is not a night-time infrared illuminated model it will go down further.

You really have to measure it and estimate hours/dary and go from there. Also test for minimum voltage it can use and remain both stable and with acceptable wifi range (probably no voltage boost circuit for wifi so output power will directly drop with input voltage) I assume it must be wifi or else you should just use power over ethernet instead.

You did not mention the application but it seems this might be a candidate for a solar panel if you really can't run wire to it.

Whether a 6V battery is the right choice depends on several variables, including cost, size, weight, ease of charging, etc. It could be more cost effective to get a 12V battery if going lead acid, suffer a buck regulator drop to 5V even if it's only 80% efficient, because you can get more battery capacity per dollar going with a readily available commodity battery rather than a specialty battery sold in smaller volumes.

Plus if you go with a 12V battery there are ready made solar panel chargers meant for vehicle battery maintenance, though with a steady current draw as significant as an IP cam you might need to put a few of those in parallel to achieve the needed supply/charge rate. In that case your battery capacity only needs to be enough to handle low light (overnight) running hours, but it greatly increases the size.

It could also create a state where if the battery ever drops too low, that when the solar panel recharges it, when it approaches a voltage high enough that the cam attempts to boot up, it could crash and be locked up until a reset, so ensuring that the battery never depletes below a measured voltage stability threshold could be very important, or use of a switch that keeps power off until the battery solar charge exceeds that threshold voltage by a good margin so it has a successful boot.