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Running multiple pi's on a tractor

Posted: Fri Jun 23, 2017 6:01 pm
by Octradox
So basically I want to run about 25 raspberry pi 3's on my tractor to monitor some stuff using the camera.

Electricity-wise, I'm concerned about the different voltages that may come out of the tractor at different revs.

What would be the most suitable way to overcome this issue? I was thinking like a big ups for all of them, or perhaps individual ups would be necessary? Could I just get away with voltage regulators?

Sorry, weird question I know...

Re: Running multiple pi's on a tractor

Posted: Fri Jun 23, 2017 8:26 pm
by SurferTim
You will need about 65 amps of 5 volt to run all those.

DC-DC power supplies would be your best bet. That will depend on the maximum voltage/current output of the tractor's generator/alternator.

Re: Running multiple pi's on a tractor

Posted: Fri Jun 23, 2017 10:55 pm
by drgeoff
SurferTim wrote:You will need about 65 amps of 5 volt to run all those.
I'd say closer to half of that.

Re: Running multiple pi's on a tractor

Posted: Fri Jun 23, 2017 11:28 pm
by SurferTim
drgeoff wrote:
SurferTim wrote:You will need about 65 amps of 5 volt to run all those.
I'd say closer to half of that.
Oh, so a 1.25A power supply is ok on a RPi3? Seems I wasted my money buying that 2.5A wall wart as was recommended?

Re: Running multiple pi's on a tractor

Posted: Fri Jun 23, 2017 11:43 pm
by fruitoftheloom
SurferTim wrote:
drgeoff wrote:
SurferTim wrote:You will need about 65 amps of 5 volt to run all those.
I'd say closer to half of that.
Oh, so a 1.25A power supply is ok on a RPi3? Seems I wasted my money buying that 2.5A wall wart as was recommended?
No you have not: https://www.raspberrypi.org/help/faqs/#powerReqs

Re: Running multiple pi's on a tractor

Posted: Sat Jun 24, 2017 12:41 am
by mikronauts
Why on earth do you need 25 Pi3's?
Octradox wrote:So basically I want to run about 25 raspberry pi 3's on my tractor to monitor some stuff using the camera.

Electricity-wise, I'm concerned about the different voltages that may come out of the tractor at different revs.

What would be the most suitable way to overcome this issue? I was thinking like a big ups for all of them, or perhaps individual ups would be necessary? Could I just get away with voltage regulators?

Sorry, weird question I know...

Re: Running multiple pi's on a tractor

Posted: Sat Jun 24, 2017 3:46 am
by Octradox
SurferTim wrote:You will need about 65 amps of 5 volt to run all those.

DC-DC power supplies would be your best bet. That will depend on the maximum voltage/current output of the tractor's generator/alternator.

Ok, so it'll output 12 volt, do I just need to get it down to 5 volt with a buck down and it'll be fine?

Re: Running multiple pi's on a tractor

Posted: Sat Jun 24, 2017 5:48 am
by Gavinmc42
You can get those car cigarette lighter power to USB adapters for a few dollars.
These have 12 to 5volt converter chips in them.
Better to have many of these than just one big power supply.

Re: Running multiple pi's on a tractor

Posted: Sat Jun 24, 2017 5:58 am
by mosespi
Octradox,

Yes, a DC-DC converter is what is needed here. Some numbers for you..

- A Pi 3 with camera recording and all CPU cores going full bore will take about 1.0 amp or so, say 1.2 amp to be safe. I am assuming you don't have any other large power draws on the Pi, high draw USB devices for example.
- Convert it to watts so you can compare things easier.. so it becomes 1.2 amp x 5 volts = 6 watts.
- Most DC converters are about 85% efficient or so.. so to give you 6 watts you are doing to need to start with about 7 watts.
- 7 watts per Pi x 25 Pi = 175 watts
- Your 12v (is it 12v and not 24v right?) system will need to supply this power.. which in amps is 175w / 12v = 14.6 amps. You can go with 20 amps to be safe. You can also use 14v for your calculation, as this is what a running 12v alternator system usually provides, not too much of a difference and you should spec a little higher when you are building this anyway.

Most cars are OK with an additional 15 amp draw. Unless it's a really small tractor I would assume it's alternator could handle an additional 15 amp load, which is about what a bright pair of lights will draw. Google the alternator output of your tractor. If you can fit 25 cameras on it, it should have a pretty big alternator!

The 2.5 amp recommendation for the Pi 3 is for a worst case power draw condition. It's a spec that covers nearly all use cases. Most people will never see this amount of draw in normal use and is actually difficult in practice to get it to pull this much power.

EDIT: I would probably use individual DC-DC converters for each Pi instead of one large one, just to avoid failing parts (Pi or converters) from taking out your whole tractor Pi array!

You will need to figure out a suitable tap point for this power and how you will be switching this power. I generally like to go close, if not directly to, the battery to avoid as much bus noise as possible.

The UPS and proper shutdown of the Pi is a whole other story and I've got some advice on that too if you want.

Plan it out, build a couple and see how it goes. And do tell us what the end goal is, as 25 cameras on a single vehicle does seem kind of mad! An interesting kind of mad.. :twisted:

Regards,
-Moses

Re: Running multiple pi's on a tractor

Posted: Mon Jun 26, 2017 1:09 am
by Imperf3kt
Monkey wrench:
Can your alternator handle the amperage?
Take for example my car - it has a 110A alternator in it (which is larger than a standard alternator as I own a v8). The battery has 90 minutes 'reserve'.

Essentially, if my alternator cannot supply enough current to everything in the car, my battery will be dead in 90 minutes.
The car and electronics use ~80A, leaving me ~30A buffer. What does your tractor use and how many A are left over? If it is less than 30-40A, you may find one day your tractor won't crank over.

Re: Running multiple pi's on a tractor

Posted: Mon Jun 26, 2017 7:58 am
by hortimech
Octradox wrote:

Ok, so it'll output 12 volt, do I just need to get it down to 5 volt with a buck down and it'll be fine?
Unfortunately it will not be 12v, it will be whatever the battery voltage is when engine is not running, rising to 13.8v when the engine starts with a fully charged battery, or 14.4 (or above) if the battery is fairly flat.

Re: Running multiple pi's on a tractor

Posted: Mon Jun 26, 2017 9:12 am
by RaTTuS
Buck converters can operate from 6V-40V and step down to 5V [you can get various ones],
why do you need 35 RPi's that seems to be an awful lot/ where are you going to house them all ?

Re: Running multiple pi's on a tractor

Posted: Mon Jun 26, 2017 5:48 pm
by Octradox
hortimech wrote:
Octradox wrote:

Ok, so it'll output 12 volt, do I just need to get it down to 5 volt with a buck down and it'll be fine?
Unfortunately it will not be 12v, it will be whatever the battery voltage is when engine is not running, rising to 13.8v when the engine starts with a fully charged battery, or 14.4 (or above) if the battery is fairly flat.
Ok, but do buck down converters have a bit of tolerance for this?

Re: Running multiple pi's on a tractor

Posted: Mon Jun 26, 2017 5:51 pm
by Octradox
mosespi wrote:Octradox,

Yes, a DC-DC converter is what is needed here. Some numbers for you..

- A Pi 3 with camera recording and all CPU cores going full bore will take about 1.0 amp or so, say 1.2 amp to be safe. I am assuming you don't have any other large power draws on the Pi, high draw USB devices for example.
- Convert it to watts so you can compare things easier.. so it becomes 1.2 amp x 5 volts = 6 watts.
- Most DC converters are about 85% efficient or so.. so to give you 6 watts you are doing to need to start with about 7 watts.
- 7 watts per Pi x 25 Pi = 175 watts
- Your 12v (is it 12v and not 24v right?) system will need to supply this power.. which in amps is 175w / 12v = 14.6 amps. You can go with 20 amps to be safe. You can also use 14v for your calculation, as this is what a running 12v alternator system usually provides, not too much of a difference and you should spec a little higher when you are building this anyway.

Most cars are OK with an additional 15 amp draw. Unless it's a really small tractor I would assume it's alternator could handle an additional 15 amp load, which is about what a bright pair of lights will draw. Google the alternator output of your tractor. If you can fit 25 cameras on it, it should have a pretty big alternator!

The 2.5 amp recommendation for the Pi 3 is for a worst case power draw condition. It's a spec that covers nearly all use cases. Most people will never see this amount of draw in normal use and is actually difficult in practice to get it to pull this much power.

EDIT: I would probably use individual DC-DC converters for each Pi instead of one large one, just to avoid failing parts (Pi or converters) from taking out your whole tractor Pi array!

You will need to figure out a suitable tap point for this power and how you will be switching this power. I generally like to go close, if not directly to, the battery to avoid as much bus noise as possible.

The UPS and proper shutdown of the Pi is a whole other story and I've got some advice on that too if you want.

Plan it out, build a couple and see how it goes. And do tell us what the end goal is, as 25 cameras on a single vehicle does seem kind of mad! An interesting kind of mad.. :twisted:

Regards,
-Moses
Thanks. End goal is to put them on a spray rig. One camera per metre on a 24m boom. The 25Th pi is just a touch screen controller for settings.

Re: Running multiple pi's on a tractor

Posted: Mon Jun 26, 2017 6:10 pm
by drgeoff
Octradox wrote:End goal is to put them on a spray rig. One camera per metre on a 24m boom. The 25Th pi is just a touch screen controller for settings.
Pay due consideration to location of the dc-dc converters and the wiring to the RPis. For example, if the 5 volt supply is at the other end of the boom from a RPi, that means 24 metres of wire (or 48 metres if not using the metalwork as ground return) giving a voltage drop.

Re: Running multiple pi's on a tractor

Posted: Tue Jun 27, 2017 2:21 am
by Octradox
drgeoff wrote:
Octradox wrote:End goal is to put them on a spray rig. One camera per metre on a 24m boom. The 25Th pi is just a touch screen controller for settings.
Pay due consideration to location of the dc-dc converters and the wiring to the RPis. For example, if the 5 volt supply is at the other end of the boom from a RPi, that means 24 metres of wire (or 48 metres if not using the metalwork as ground return) giving a voltage drop.
Wouldn't it be 12m as you go from the centre out? Shouldn't voltage drop not matter since we're turning the voltage down for the pi's anyway?

Re: Running multiple pi's on a tractor

Posted: Tue Jun 27, 2017 3:07 am
by Imperf3kt
You can do it like that, sure, but I imagine you'd need multiple buck converters. DC doesn't travel very far. 12M even, will be too far.

Re: Running multiple pi's on a tractor

Posted: Tue Jun 27, 2017 3:26 am
by Octradox
Imperf3kt wrote:You can do it like that, sure, but I imagine you'd need multiple buck converters. DC doesn't travel very far. 12M even, will be too far.
Can't I just have a big wire to minimise resistance?

Re: Running multiple pi's on a tractor

Posted: Tue Jun 27, 2017 3:49 am
by Imperf3kt
Octradox wrote:
Imperf3kt wrote:You can do it like that, sure, but I imagine you'd need multiple buck converters. DC doesn't travel very far. 12M even, will be too far.
Can't I just have a big wire to minimise resistance?
I calculated the load with copper wire @2A, 12M and 5v to be possible with 10AWG wire. Thats one massive wire for a Pi.
Using 10AWG, you can expect a maximum voltage of 4.86v at your furthest Pi

Assuming your Pi and accessories use exactly 0.5A, you could get away with a minimum of 18AWG which will give you 4.75v - the bare minimum recommended voltage for a Pi.
You'd also need a LOT of wire. Each would need to be connected in parallell, meaning over a hundred and fifty meters of copper wire.
I doubt one buck converter will handle all that current, so multiple of those. 25 Pis, 24 cameras, one monitor...
The costs are climbing into some pretty heavy numbers here.

I suppose your best approach would be one wire from 12v that you connect to 24 buck converters that are right next to the Pi they will power.
But this is getting too complicated for my limited knowledge on electronics.

Re: Running multiple pi's on a tractor

Posted: Tue Jun 27, 2017 4:48 am
by Octradox
Imperf3kt wrote:
Octradox wrote:
Imperf3kt wrote:You can do it like that, sure, but I imagine you'd need multiple buck converters. DC doesn't travel very far. 12M even, will be too far.
Can't I just have a big wire to minimise resistance?
I calculated the load with copper wire @2A, 12M and 5v to be possible with 10AWG wire. Thats one massive wire for a Pi.
Using 10AWG, you can expect a maximum voltage of 4.86v at your furthest Pi

Assuming your Pi and accessories use exactly 0.5A, you could get away with a minimum of 18AWG which will give you 4.75v - the bare minimum recommended voltage for a Pi.
You'd also need a LOT of wire. Each would need to be connected in parallell, meaning over a hundred and fifty meters of copper wire.
I doubt one buck converter will handle all that current, so multiple of those. 25 Pis, 24 cameras, one monitor...
The costs are climbing into some pretty heavy numbers here.

I suppose your best approach would be one wire from 12v that you connect to 24 buck converters that are right next to the Pi they will power.
But this is getting too complicated for my limited knowledge on electronics.
Was planning on doing one buck down each. Your calculation is at 5v. But it's outputting 12v, so it shouldn't be an issue.

Cost shouldn't matter too much. Losing roughly 30k a year by not having this machine.

Re: Running multiple pi's on a tractor

Posted: Tue Jun 27, 2017 5:22 am
by Imperf3kt
To be perfectly honest, I think a simpler solution might just be to invest in one of those wireless CCTV systems. I know they can do multiple cameras, but I don't know about 24!.

Re: Running multiple pi's on a tractor

Posted: Tue Jun 27, 2017 5:43 am
by Octradox
Imperf3kt wrote:To be perfectly honest, I think a simpler solution might just be to invest in one of those wireless CCTV systems. I know they can do multiple cameras, but I don't know about 24!.
That won't be able to do enough image analysis at fast enough rates. Plus I need IO to drive solenoids.

Re: Running multiple pi's on a tractor

Posted: Tue Jun 27, 2017 5:49 am
by Octradox
Anyway. Thanks for all the advice guys, I'll put a simple buck down on each Pi I think. Shutdown isn't needed as I have a button on the controller for it (and also if it loses connection it'll shutdown). Price is pretty fine, I did calculations and reckon I can do it for 10- 15k which is cheap for what I'm hoping it will do.

I'll let everyone know what happens after its hooked up. Currently waiting to get the money but this will go ahead :)

Re: Running multiple pi's on a tractor

Posted: Tue Jun 27, 2017 11:18 am
by Gavinmc42
I have a Pi security camera at the end of 20+m of cat 5 DIY PoE setup.
12Vin and a $2 12volt to 5V USB cigarette adapter, ripped open for the circuit.
Been working for years.

Only a 12m boom, thicker cable would be used and half the Pi's are only 6m away.
Pay a bit more and I would use TO-220 Voltage regulator Switch mode version of a LM7805.
Some have lowdrop out down to 5.5V and 36V? input, available from 500ma to 2amps+.

I will assume you are using Pi3 with camera for spot location spraying.
The 12Volt solenoids will need 1amp too?

You could use a Cat5 12V PoE but bunch of 12 cables per boom gets a bit big.
Hmm, actually cat5/6 cables can be got at various lengths for quite low prices, this could save a lot of cabling costs.

How are you controlling the Pi's Ethernet or RS485/CAN?

Re: Running multiple pi's on a tractor

Posted: Tue Jun 27, 2017 12:43 pm
by Octradox
Gavinmc42 wrote:I have a Pi security camera at the end of 20+m of cat 5 DIY PoE setup.
12Vin and a $2 12volt to 5V USB cigarette adapter, ripped open for the circuit.
Been working for years.

Only a 12m boom, thicker cable would be used and half the Pi's are only 6m away.
Pay a bit more and I would use TO-220 Voltage regulator Switch mode version of a LM7805.
Some have lowdrop out down to 5.5V and 36V? input, available from 500ma to 2amps+.

I will assume you are using Pi3 with camera for spot location spraying.
The 12Volt solenoids will need 1amp too?

You could use a Cat5 12V PoE but bunch of 12 cables per boom gets a bit big.
Hmm, actually cat5/6 cables can be got at various lengths for quite low prices, this could save a lot of cabling costs.

How are you controlling the Pi's Ethernet or RS485/CAN?

Yeah, 2 solenoids per meter. I'll have a look at some of the stuff you suggested.

I'm using the WiFi atm. Have one set as a server, using socket. Can even send altered video through. Helps with selecting the settings. Am a bit worried if the WiFi can handle all that/ the distance, but worst to worse, I'll hardwire it up Ethernet style.

Having lots of cables is fine. But if it's avoidable why would you do it.