Hi there.

I am a total novice when it comes to understanding power supplies and the like. Last year I built myself a multi-camera rig in order to produce realistic human 3D models for animation. I am looking this year to improve on my build. One such area for improvement would be its power supply. Currently each camera has a dummy battery connected to a mains transformer ( https://www.amazon.co.uk/PremiumDigital-Canon-Replacement-Power-Adapter/dp/B00841UIOU )... very messy cables and lots of multi plugs. I would like to remove all the individual power supplies and replace them with a single transformer or even a couple to service all the cameras. At the moment the rig uses 18 canon eos 400d cameras but I plan to double this number so wish to accommodate scalability. Any formulas on how to calculate what I would need a transformer to deliver or any help/guidance would be much appreciated (I do dislike having to cable tie transformers together to try to make them tidy)

 

You may be able to use that power supply to power all the cameras, since it has a 2A output.
How much current does each camera take?

 

You may be able to use that power supply to power all the cameras, since it has a 2A output.
How much current does each camera take?

I don't know what each camera 'draws' and the only figures I can see are DC 8.1v on camera body, 7.4v 720mah on batteries and output 7.4v 2A on the SC adapters. Is there a way I can test the current draw of the camera ?

 

You should be able to measure current draw of one of those cameras using a power coupler - a "dummy battery" (and you can get those separately https://www.ebay.com/i/192587228960?chn=ps) and making your own cable with leads so that you can insert your meter into the circuit...have you used a meter to measure current before?.

I would be amazed, however, if you could operate 36 cameras off of that 2A supply. That is 55 mA/camera and I think it is way to low, but I could be wrong. Remember, the current draw from the camera is going to vary with the use of various functions like the flash, the LCD screen, auto focus servos and not just the shutter. But you could examine the current requirements to guide you.

Because that camera is designed to only run on batteries, you are probably going to have to use a power coupler like I posted (edit: and which you already have as part of the external power supplies), and you could power more than one camera with a supply...but not likely 36 with that supply.

 

Thankyou Raymond.. I have flirted with a meter before to test circuits so will give this a go I do have all the necessary power couplers as well as a few old defunct batteries I can modify into couplers if needed. Once I've worked out the power need of a camera I would then need to source a suitable replacement ac adapter.. I've got one of these hhttps://www.wholesaleledlights.co.uk/led-strip-lights/led-power-supplies/150w-led-driver.html that I use to power 7 odd metres of LED strip lighting.. Is this the sort of power supply I should be looking at ? I can't seem to find any 7.4v supplies with anymore than 2A.

 

Thankyou Raymond.. I have flirted with a meter before to test circuits so will give this a go I do have all the necessary power couplers as well as a few old defunct batteries I can modify into couplers if needed. Once I've worked out the power need of a camera I would then need to source a suitable replacement ac adapter.. I've got one of these hhttps://www.wholesaleledlights.co.uk/led-strip-lights/led-power-supplies/150w-led-driver.html that I use to power 7 odd metres of LED strip lighting.. Is this the sort of power supply I should be looking at ? I can't seem to find any 7.4v supplies with anymore than 2A.

I think that you should get a handle on estimating how much current you use/need first. If I am understanding correctly, you already have 18 power supplies. If you add 18 more cameras and you get (or already have) 18 more power couplers, you may be able to simply use one power supply for two cameras but each camera is going to need a coupler. Maybe you can run four cameras with one of you existing 2A supplies. Maybe more, maybe less, I don't know, but you will have an idea after you measure the current consumption of one (or more) cameras.

While you don't *have* to make a cable to measure the current with a meter (you could splice into an existing cable before it goes to the coupler, measure the current, and then solder it back together) it will be cleaner if you make a little cable and you can use that cable with multiple supplies/cameras for testing. One end would have a jack like the one on the coupler and the other a plug like that on the power supply that goes into the coupler. Remember, you are measuring current so you will break into only one of the two power wires and your meter leads will bridge the ends of that wire. Sorry if it seems like I am talking down to you, I am just being cautious and want to make sure that you know how to measure the current - so if that is unclear please ask questions.

Edit: and BTW, the power supply that you linked to is 12/24 volts output - right? and that would probably damage the cameras. This is another reason to use some of the power supplies that you already have and that already work correctly.

 

No, you are definitely not talking down to me You've given me exactly what I need to hear. I am a self declared novice but I do like to learn new things and to understand how things work..
So my first step will be to knock up a little cable to facilitate easier splicing into the supply circuit , enabling me to monitor the current draw as I switch on the camera (or cameras) and operate it. Next step would be to take that value and multiply it by the number of devices (or relevant factor if my current reading is for 2 cameras). So.. once I have that in hand this would leave me with the figures 7.4v, and an ampage value for all the cameras (lets say 200ma x36 =7.2A). So, on the premise of the theoretical figures mentioned, would this be a suitable supply https://www.tme.eu/gb/details/rsp-75-7.5/built-in-power-supplies/mean-well/ ?
I understand the principle of powering say 3 or more cameras from one of the supplies I already have and will most likely be the route I initially adopt just to make things tidier. At the moment with the 18 cameras I have on 6 columns (3 cameras per upright) running 3 cameras from 1 of my existing supplies would work fine but it wouldn't enable me to scale the number of cameras in a column to say 5 without adding another power supply(and plug). At the moment the 18 cameras cover 180 degrees of a circle and in the grand scheme of things I would just build another rig identical to provide 360 degree coverage. So, in my head 'in the grand scheme of things' the simplicity of 2 power supplies per half of the rig (1 for cameras, 1 for LED lights) greatly appeals to me.

 

No, you are definitely not talking down to me You've given me exactly what I need to hear. I am a self declared novice but I do like to learn new things and to understand how things work..
So my first step will be to knock up a little cable to facilitate easier splicing into the supply circuit , enabling me to monitor the current draw as I switch on the camera (or cameras) and operate it. Next step would be to take that value and multiply it by the number of devices (or relevant factor if my current reading is for 2 cameras). So.. once I have that in hand this would leave me with the figures 7.4v, and an ampage value for all the cameras (lets say 200ma x36 =7.2A). So, on the premise of the theoretical figures mentioned, would this be a suitable supply https://www.tme.eu/gb/details/rsp-75-7.5/built-in-power-supplies/mean-well/ ?
I understand the principle of powering say 3 or more cameras from one of the supplies I already have and will most likely be the route I initially adopt just to make things tidier. At the moment with the 18 cameras I have on 6 columns (3 cameras per upright) running 3 cameras from 1 of my existing supplies would work fine but it wouldn't enable me to scale the number of cameras in a column to say 5 without adding another power supply(and plug). At the moment the 18 cameras cover 180 degrees of a circle and in the grand scheme of things I would just build another rig identical to provide 360 degree coverage. So, in my head 'in the grand scheme of things' the simplicity of 2 power supplies per half of the rig (1 for cameras, 1 for LED lights) greatly appeals to me.

I would like to see your project so if you ever want to post some pics or link to a movie, that would be great because it sounds cool.

Basically, I think that you have a decent plan. Here are two caveats...

1. When you are measuring the current, you are likely to see some quick swings when some function (like autofocus) is going on. You may need to try your best to estimate what the value of that spike is from the meter display. Some of that is going to be meter-dependent and I don't know if mine has any kind of time averaging, but some might. On this point I would ask someone else who knows more than I do - i.e., @crutschow about the best way to deal with that because I am thinking that a peak draw, even for a short period of time, is going to be of interest as is an average draw over some period of time. Further, since many cameras are involved, you would want to be conservative and assume the case that all will draw the maximum together at some time. I would compensate by using a PS that was gave me a lot of room for error (like twice what I think I need), largely because I don't know any better. Not to stray too far, but I just got a new Canon dslr and I was just looking at their battery life estimates and they have table with columns of number of pics, pics with flash, and notations about how autofocus will reduce the numbers.

2. About the power supply. Well, the voltage would seem ok - 7.4 vs 7.5, but you may want to look at the specs on the battery that the XTi uses (actually I have one, but you have 18, so you can look . Then there is an issue of regulation - again, I would defer to the more experienced, like @crutschow What I like about the PS that you have is that you *know* from experience that they can reproduce the battery output as far as the Canon is concerned. But, I was surprised that they were 2A supplies when they are only covering that one battery - that is another reason why it is so important to do some measuring first. All I could give you about some of those details is a "well it seems like it might work".

Hope this helps.

 

So what is the battery used in the camera and how long will it typically last before it dies?

 

The battery that comes with the 400D (Rebel XTi) is an NB-2LH 7.4V, 1800 mAh, (correction) 5.9 Wh https://www.amazon.com/NB-2LH-Battery-Canon-Camera-Video/dp/B01C2859YO

How long it typically lasts depends. Camera folks typically talk about how many shots can be taken, with or without flash etc... - see this thread for an example https://www.dpreview.com/forums/thread/2056500

I just looked in the manual and I do not see a shot estimate (my earlier reference is to a new camera that I just got). I do have an XTi and have had it for a good 6-7 years I guess. Good old camera, but for the life of me, I could not tell you an average # of shots on a battery charge. Maybe the OP has information on this.

 

An anecdotal story:

I once had a project where I needed to power 12 little LCD TV sets that were normally powered by batteries.

They were normally powered by 4 X AA batteries, I measured the current, bought a 6V switching supply and wired it all up.

The damn thing would not work!

The TV's had a nasty property- a very large spike of current was required to start them up, 3X the running draw.
My little switch mode supply saw this as a short and refused to start into the load.

What I failed to do was fully characterize the loads, If I had, I would have known that I needed a much bigger power supply to start them all at once. What made this extra evil was the fact I had NO ROOM for a larger PSU, I ended up painfully building a complex power sequencing circuit to fix the problem, the power supply could start one, but not all at the same time.

What seemed like a quick project turned into a money-losing nightmare.
Looking like an idiot in front of the client.

 

Well.. the batteries I have are all old ... but according to the spec they accommodate 280-360 shots dependent on temperature... with a caveat of you will be able to take more if you don't use flash and preview... so not very helpful.
The figures I have are 'DC 8.1v ' on camera body, '7.4v 720mah' on batteries and 'output 7.4v 2A' on the AC adapters.
I wouldn't be surprised to see a spike as mentioned by @Sensacell which is maybe why the camera has a slightly higher voltage requirement.
Just putting a meter on the power supply and battery show that the AC adapter provides 7.6v (I remember when searching for the power supplies that some people did say the voltage was a touch low but mentioned no issues caused by it) and the battery 8.1v. Would I then use a 9v powersupply ?
Function wise the cameras will be used in a very specific fashion.. switch on, LCD on, focus and check/adjust fstop under lighting, passive external trigger, review of shots (displayed on LCD).. The LCD's need to be on all the time and the taken image previewed automatically. All cameras are linked to a laptop vis USB to enable checks and download of images. So I can test current draw specifically for those tasks.
Currently all the cameras are 400D but I will be upgrading to 600D this year.. using the 400D's to cover the back 180degrees of the subject whilst the 18mp 600D's take over the front.
Some piccies