Author Topic: Noob Question about voltage requirements  (Read 2571 times)

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Offline SylvestreTopic starter

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Re: Noob Question about voltage requirements
« Reply #30 on: August 21, 2011, 03:59:35 PM »
So what voltage regulators will I need, how many AH will the battery be for the electronics (everything besides motors), and what will the circuitry look like?  Specs are posted above of all the electrical components

Offline adanvasco

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Re: Noob Question about voltage requirements
« Reply #31 on: August 22, 2011, 11:38:15 AM »
You might as well use two different power supplies by separating the circuits. Take a look at the $50 robot tutorial and you'll get an idea on how to do this.
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Offline SylvestreTopic starter

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Re: Noob Question about voltage requirements
« Reply #32 on: August 22, 2011, 03:01:40 PM »
That's what I had in mind (I said this in an earlier post).  I'm going to have one battery for the motors and one battery for the electronics (everything except motors and motor driver).  Basically, I'm just looking for what my circuit will look like, what regulators I need, the battery I need for my electronics, and if there is any other things I need/ should know.

Offline Soeren

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Re: Noob Question about voltage requirements
« Reply #33 on: August 22, 2011, 03:16:08 PM »
Hi,

So what voltage regulators will I need, how many AH will the battery be for the electronics (everything besides motors), and what will the circuitry look like?  Specs are posted above of all the electrical components
You seem to think that we're somehow obliged to do your footwork?

You add the max. current consumptions of each unit that you want to be supplied by the +5V line.
If that comes to eg. 2A, you need a 2Ah battery for 1 hour of runtime and 3Ah for 1.5 hour.
Actually, you need to get a somewhat higher capacity battery, as the capacity rating is for a 20 hour discharge and the capacity falls with rising current draw and the battery is gonna get worn over time as well, so go for 30% to 50% more capacity than your calculations indicate.

When you have calculated the total consumption on the +5V line, it's time to start adding a regulator.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline SylvestreTopic starter

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Re: Noob Question about voltage requirements
« Reply #34 on: August 22, 2011, 04:44:25 PM »
Ok thank you.  I'm sorry, but I am just looking for some help and a starting point.  That's all.  That's exactly what you gave me.  Thanks.

So I added up all of the current draws for the hardware that'll be on the electrical battery and I got about 3 amps or 3051 ma (I did not add up the current the Axon II draws).  So if I wanted it to run for 1.5 hours I assume I should use a 10-15 AH battery just to be safe (considering I didn't add the current required from the Axon II), or am I wrong?

I am still a bit confused on the regulators though?  How do I figure out which one I need?

Offline rbtying

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Re: Noob Question about voltage requirements
« Reply #35 on: August 22, 2011, 06:56:28 PM »
If you need 3A at 5V, you get a regulator (preferably a switching one) which is rated for 5-6A or more at 5V. Usually a good choice for this amount of current is an R/C "BEC", which are commonly rated at ~5A/5V. Another option would be one of these.

And no, not quite: 3A * 1.5 hrs = 4.5 Ah, then overspec the battery leads to 7-8Ah. Of course, a 10-15 Ah battery will work, it'll just be large/expensive/heavy.

Offline SylvestreTopic starter

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Re: Noob Question about voltage requirements
« Reply #36 on: August 22, 2011, 08:33:52 PM »
If I wanted the Axon II and the video transmitter and receiver to run on 12 volt  I won't need a regulator, right?  If I need to boost the voltage from 12 volt to 24 volt, will I need a voltage regulator work or does the the Sabertooth motor driver take care of that?

Offline SylvestreTopic starter

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Re: Noob Question about voltage requirements
« Reply #37 on: August 22, 2011, 10:42:10 PM »
Just drew up this schematic.  I will definitely take criticism because I know I did something wrong  ;D.  I still have the same questions as I did in the post above.  Where it got cut off, it says 12 volt 12 AH battery.  I forgot a few things; a fuse in between battery and motor driver and an IC to measure how much battery I have left.  Also the wireless rf modem that connects to the UART and power of the Axon II
« Last Edit: August 25, 2011, 02:01:06 PM by Sylvestre »

Offline SylvestreTopic starter

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Re: Noob Question about voltage requirements
« Reply #38 on: August 24, 2011, 09:22:08 PM »
Also, there will be a 5 volt cooling fan

Offline Soeren

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Re: Noob Question about voltage requirements
« Reply #39 on: August 25, 2011, 01:21:25 PM »
Hi,

Just drew up this schematic.  I will definitely take criticism because I know I did something wrong  ;D
And right you are...  :D


I still have the same questions as I did in the post above. 
Please post by using "modify" instead of chain posting, or answers will either not happen, be confusing or, as I have decided to do, just happen to a single of several chain posts.


Where it got cut off, it says 12 volt 12 AH battery. 
Using two batteries of 12V doesn't make sense. In that case it would be better to just use one.


I forgot a few things; a fuse in between battery and motor driver and an IC to measure how much battery I have left.
Instead, you added capacitors and they'll be fine as fuses, restricting any bit of current flow at all  ;)
Most of the writing on the "schematic" is intelligible and the bit in the middle, right of the controller is a bit of a mystery to me?

'And no, no motordriver will make the 12V into 24V and even if it did, that would mean a current draw from the battery of more than 88A!

You could draw such diagrams in Eagle with 100% clarity.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline SylvestreTopic starter

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Re: Noob Question about voltage requirements
« Reply #40 on: August 25, 2011, 01:59:54 PM »

Quote
Using two batteries of 12V doesn't make sense. In that case it would be better to just use one.

I would use two batteries to avoid brownouts. 

Quote
right of the controller is a bit of a mystery to me?

Basically, that's just the wireless camera setup (transmitter, receiver, camera).

Quote
And no, no motordriver will make the 12V into 24V and even if it did, that would mean a current draw from the battery of more than 88A!

Could I use a boost converter to boost the voltage?


Will I need any voltage regulation to output a steady voltage?


Offline Soeren

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Re: Noob Question about voltage requirements
« Reply #41 on: August 25, 2011, 02:48:39 PM »
Hi,

I would use two batteries to avoid brownouts. 
All your logic runs on a regulated 5V. This leaves a very wide margin for voltage drops of the battery before they would get through to the logic and if you fear that's gonna happen with a correct wired and sound battery, a power buffer for the logic is easy to implement.
Assuming the bare logic takes 100mA (it's probably less) and the brownout time is 10ms (it's probably shorter), then a diode and a 220µF capacitor will make sure the supply keeps the voltage OK.


Basically, that's just the wireless camera setup (transmitter, receiver, camera).
Aha. Why would you have a receiver on the 'bot?


Could I use a boost converter to boost the voltage?
Yes, if you're able to make a boost switcher for such high currents. You will find it hard to get an efficiency of more than 80%, Which means the peak current will be huge.

This sets quite hard demands for the battery and the input capacitors of the switcher and since the average drain will be around 110A (including losses), you'd need a battery of more than 200Ah for a 1.5 hour runtime.

It would be fair to tell you that a I know several experienced engineers that wouldn't touch such a project with a long stick.
Neither would I, as the sensible way to get the 24V in your app. is to connect two 12V batteries in series (same type, age and capacity).


Will I need any voltage regulation to output a steady voltage?
Yes.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline SylvestreTopic starter

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Re: Noob Question about voltage requirements
« Reply #42 on: August 25, 2011, 03:15:41 PM »
Quote
All your logic runs on a regulated 5V. This leaves a very wide margin for voltage drops of the battery before they would get through to the logic and if you fear that's gonna happen with a correct wired and sound battery, a power buffer for the logic is easy to implement.
Assuming the bare logic takes 100mA (it's probably less) and the brownout time is 10ms (it's probably shorter), then a diode and a 220µF capacitor will make sure the supply keeps the voltage OK
Ok thank you for the advice on the capacitor.  I'll do that instead of using a separate battery to power the motors.

Quote
Aha. Why would you have a receiver on the 'bot?
Oh man I am getting my terms mixed up :P.  I meant to say just the transmitter and camera.

Quote
It would be fair to tell you that a I know several experienced engineers that wouldn't touch such a project with a long stick.
Neither would I, as the sensible way to get the 24V in your app. is to connect two 12V batteries in series (same type, age and capacity).

Yes that is a brilliant idea.  The solution you explained would be more than I could handle (money and knowledge).  I'll buy two 12 volt 75 AH batteries.


If I use capacitors to regulate the motors and the Axon II already has on board regulation will I still need regulators?

Offline Soeren

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Re: Noob Question about voltage requirements
« Reply #43 on: August 25, 2011, 03:41:27 PM »
Hi,

If I use capacitors to regulate the motors and the Axon II already has on board regulation will I still need regulators?

Capacitors doesn't regulate and I'm not sure what you mean?

As I already mentioned, you have to find a datasheet for the regulator used on the Axon and see what input it can handle.
You shouldn't tap 12V from one of the series connected batteries, as that will unbalance their charge.

A simple buck switcher taking the 24V down to 6..8V would be the best way to feed from the two series connected batteries. You could use more than one switcher.

If you use something like this and change ZD1 to somewhere around 7..8V, you'd get a reasonable input for 5V LDO's (with a peak efficiency of around 94% at 200mA and still in the high eighties at 7he max. of 700mA).
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline SylvestreTopic starter

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Re: Noob Question about voltage requirements
« Reply #44 on: August 25, 2011, 04:13:39 PM »
My motor driver will regulate the current and voltage applied to my motors. Could I use a product like this to regulate the voltage and current applied to the electronics (everything besides motors)?

http://www.google.com/products/catalog?hl=en&rlz=1C1RNCC_enUS321US321&q=dc+to+dc+converter+12+volt+5+amp&gs_upl=6799l10714l2l10790l6l5l0l0l0l0l214l615l0.3.1l4l0&bav=on.2,or.r_gc.r_pw.&biw=1280&bih=666&um=1&ie=UTF-8&tbm=shop&cid=3288733956479599320&sa=X&ei=APJWTsfFC8eKsQLPmdW3DA&ved=0CHkQ8wIwAg
« Last Edit: August 25, 2011, 07:08:53 PM by Sylvestre »

Offline Soeren

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Re: Noob Question about voltage requirements
« Reply #45 on: August 25, 2011, 09:24:07 PM »
Hi,

My motor driver will regulate the current and voltage applied to my motors. Could I use a product like this to regulate the voltage and current applied to the electronics (everything besides motors)?

http://www.google.com/products/catalog?hl=en&rlz=1C1RNCC_enUS321US321&q=dc+to+dc+converter+12+volt+5+amp&gs_upl=6799l10714l2l10790l6l5l0l0l0l0l214l615l0.3.1l4l0&bav=on.2,or.r_gc.r_pw.&biw=1280&bih=666&um=1&ie=UTF-8&tbm=shop&cid=3288733956479599320&sa=X&ei=APJWTsfFC8eKsQLPmdW3DA&ved=0CHkQ8wIwAg

What did the datasheet on the voltage regulator say?
And how high a voltage will the rest of the equipment handle?
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline SylvestreTopic starter

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Re: Noob Question about voltage requirements
« Reply #46 on: August 25, 2011, 09:43:08 PM »
Here are the main specs:

INPUT voltage 20 to 32 VDC
OUTPUT voltage 13.8 VDC
Efficiency >92 %
Output current: 5 amps
max output current: 5.5 amps

Datasheet URL:
http://www.samlexamerica.com/customer_support/pdf/SlickSheets/SDC-5_Samlex_Specifications.pdf

The axon II can handle 5-15 input voltage
The transmitter and camera just says it requires a 12 volt input voltage

« Last Edit: August 26, 2011, 10:16:33 AM by Sylvestre »

 


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