Need someone to design and make a basic circuit (UK)

[SamSpurgeon]

Hi there,

Hoping this is the right place to post! I am currently in the process of building an underwater camera housing. This housing will be tethered to the surface and I need a circuit (that will be housed inside a peli case) to manage power. It's just a one off at the moment (so maybe two so I have a backup). If you are interested, it would be great to find out a rough idea of cost. The circuit will be as follows. I'll need someone to both design and manufacture the circuit:

- 2 x power inputs (1 x 24v positive and ground, 1 x 12v positive and ground) on the surface.
- 3 x power wires going down to the housing (1 x 12v positive, 1 x 24v positive and a shared ground)
- 2 x power outputs on the surface (1 x 24v pos and ground, 1 x 12v pos and ground)

The logic is:

- if only the 12v power supply is plugged in, only 12v gets fed down to the housing (unregulated direct from the power supply). On the surface, 12v is regulated to 24v and 12v for the two outputs
- if only the 24v power supply is plugged in, only 24v gets fed down to the housing (unregulated direct from the power supply). On the surface, 24v is regulated to 24v and 12v for the two outputs
- if both 24v and 12v supplies are plugged in, the 12v and 24v cables to the housing are live (unregulated direct from the power supply), sharing the ground. On the surface, input voltage from one of the sources (is it best that 24v takes priority? Happy to take a lead on this) is regulated to 24v and 12v for the two outputs.
- the inputs are batteries and not constant voltages. 12 could be 16v to 9v and 24v could be 30v to 20v. Would be good to have some kind of LCD readout for voltages too.

- the outputs for the housing only need to be wired to a connector in the peli case (I can do this) - no need to worry about marine cabling etc I already have that covered!

Thanks!

Sam

 

[GPG]

Why two supplies? This is the converter topology that will do buck/boost
http://www.ti.com/lit/an/slyt309/slyt309.pdf
Google voltmeter module . There are heaps of them.

 

[SamSpurgeon]

Hi, thanks for your response. The camera packages will ship with either 12v block batteries for the surface or 24v blocks depending on the input voltage of the camera. I'd like to be able to cater for either. It's unlikely there will be two input voltages but I'd like to cater for that too just in case. The industry standard inputs are 4 pin XLR for 12v and 3 pin XLR for 24v so it's not like I could just have one input that you could plug either a 12 or 24v battery into.

That convertor you linked to looks great and also I am aware there are many voltmeters. I am looking for someone to build this circuit for me exactly as specified as I am tied up trying to make sure the thing doesn't leak!

Thanks

Sam

 

[AnalogKid]

I tried to sketch the interconnects based on post #1 and got lost. Can you sketch what goes where?

ak

 

[SamSpurgeon]

OK please bear with me - my electronics knowledge is limited so I don't know if the way I've drawn it is even correct but here it is:

- two power sources are on the left
- the positives from each go to the housing with a shared GND
- if only one of the sources is plugged in (eg 24v only), there will only be one voltage going down to the camera.
- the regulator/logic box (this is the real unknown for me) takes 24v and 12v positive in as well as a GND.
- it's logic determines which source has a battery plugged in and taking that battery's power, it provides a both regulated 24v and 12v feed to two connectors on the surface (if both sources are plugged in, ie there's both a 12v and 24v feed then it will use whichever is best from an electronics standpoint).
- the thinking behind it is that no matter whether you have a 12v camera or a 24v camera using 24v or 12v power from the surface, there will always be a need for BOTH voltages to be available via the sockets on the surface.
- would be great to have digital voltage readouts for both power sources.




Hope that makes things a bit clearer!

Sam

 

[AnalogKid]

Much better. What are the peak and average (if different) currents for the two sockets and the two lines to the housing. Also, are the sockets labeled correctly? You have the 24 V Socket connected to 12v+ Out.

The most efficient way will have two independent regulators. The 24 Vin has a 12 V buck, the 12 Vin has a 24 V boost, and steering diodes connect everything and play traffic cop. I assume that when both power sources are available you want both internal power converters bypassed. At worst, a pair of switching transistors. Most of this can be done with ebay Chinese modules. How big can theReg & Logic enclosure be, does it need to be waterproof, etc.?

ak

 

[SamSpurgeon]

Oh yes well spotted, that should be the other way round...

So the two sockets will be 2 amps each max at their respective voltages. For reference, the 12v will probably be used to power something like a TV Logic 5.5" 058 monitor which I think maxes out at about 14w consumption (the 056 previous model is 12w max). So only about 1.1a for that. The 24v socket will power a hard wired focus control handset which I don't see being more than 2a either (the website of the handset company only has power consumption for the motor driver that sits on the camera which states "The power requirements of the MDR2 are 24 - 30 VDC at .15A quiescent, 3A peak". This is for something that drives three high torque motors though, I think the handset will be nowhere near 3a).

re: regulator bypassing when both power sources are plugged in - I think the socket feeds should still be regulated so that their voltage behaviour is consistent no matter what power sources are plugged in.

As far as power down to the housing is concerned....10a for each feed at their respective voltages? Is this info required for the control circuit as it is essentially a direct, unregulated feed from the battery?

To answer your other questions - no it does not need to be sealed/waterproof, it will be housed in this:

http://www.pelican.com/us/en/product/watertight-protector-hard-cases/small-case/standard/1400/

Whilst it won't be the only component inside, it will be the one that takes up the most room (the rest will just be wires coming from an underwater connector mounted to the peli itself that split out to the various connections required (ethernet control, video feeds etc). There won't be any additional circuitry in there...

I'd like it to be as robust as possible if that means it's bigger in size then no problem.

Thanks

Sam

 

[AnalogKid]

http://www.ebay.com/itm/6-35V-to-1-...577986?hash=item4199679a42:g:ITgAAOSwjVVVoPRG

Two of these look like a good starting point. From your point of view, they take anything in and make anything out. Under worst case conditions, boosting a sagging 10 V source to 24 V 2 A out at 85% efficiency means the input current to that one regulator is over 5 A, and this module is rated for 7 A.

12 V input > 10 A OR-ing diode > 10 A breaker input
24 V input > 10 A OR-ing diode > 10 A breaker input
10 A circuit breaker / master power switch > internal master power bus

This creates a protected internal master power bus that always is at the higher input voltage. This means that when both external DC sources are connected, the 12 V source is ignored and everything runs on the 24 V. For more intelligent input power management a small control circuit would have to be designed and built.

From the internal bus:
5 A circuit breaker / 24 V power switch > 24 V output regulator > connector
5 A circuit breaker / 12 V power switch > 12 V output regulator > connector

or something like that

ak

 

[SamSpurgeon]

Thanks AK, that seems like a great solution. Always running at the higher voltage definitely seems to me in my limited understanding to be the best solution. I think I'd be pretty happy to give this a go myself, so thanks for your support. On my shopping list so far I have:

2 x voltage convertors (I found a UK supplier for your option)
http://www.ebay.co.uk/itm/6-35V-to-...768328?hash=item3d07237148:g:htEAAOSwl9BWLdf1

2 x panel mount LCD voltmeters
http://www.ebay.co.uk/itm/0-100V-LE...795499?hash=item463cebc6ab:g:nKMAAOSwyQtVh92Q

1 x hand held voltmeter to make sure all the ins and outs are as expected
http://www.ebay.co.uk/itm/Digital-L...867886?hash=item20ecdd1f2e:g:zyMAAOSwFnFWCjoO

I have to admit, after searching around for the other components, there was so much choice (eg of diodes), I wasn't really sure what the right components would be (or even look like). If you can point me in the right direction for these components, I'd be really grateful (I realise this is kind of hand holding a bit and you've already offered lots of advice so no worries if you don't have the time for this!)

Thanks

Sam

 

[AnalogKid]

Hold off on the panel meters; the tech description does not match the title.

Hand holding is what this forum does. We get cranky when someone tries to get their homework done for free, but other than that a decent question gets a decent answer.

Diodes and misc stuff will have to wait - I'm going to a REAL football game.

ak

 

[SamSpurgeon]

Oh yeah I just noticed. AC! Thanks again and talk soon...