Author Topic: odd voltage and how to handle it?  (Read 1406 times)

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Offline WizzardTopic starter

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odd voltage and how to handle it?
« on: April 19, 2009, 07:23:42 PM »
I have access to a lot of surplus 7.5 volt radio battery packs. They put out about 8.5vdc when fully charged and I want to use them to supply power for my project. I have a Axon that will be controlling my servos (6 HS7955tg's) a couple of GP2d12 ir range sensors and also a SaberTooth 2x10 running 2 7.2 volt Banebot motors.

I have a few questions?

Can I use some 7806 Voltage Regulators in parallel with a big Capacitor after them to drop the supply down for the axon, sensors, and the servos?

should I regulate the 8+ volts down for the Sabertooth and the 7.2volt Motors

Any idea what amount of current the axon, servos and the ir sensors will draw. Stall current is rated at 4200mA and no load running is 300mA at 6vdc for each of the servos but im not sure how to figure the normal amount they would use in a arm setup. I have not been able to find a data sheet for the ir sensors so if anyone has the current usage on them it would help also what does the axon itself draw?

I know that these will probably seem obvious to some of you. thanks for the help.

Wizzard. 

Offline SmAsH

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Re: odd voltage and how to handle it?
« Reply #1 on: April 19, 2009, 07:39:50 PM »
yes you can regulate the voltage down for the servos, im not sure on how much current the servos will draw t=but the axon shouldn't draw too much. and although the motors probably could take the 8V i would say rather regulate it to be safe.
Howdy

Offline Razor Concepts

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Re: odd voltage and how to handle it?
« Reply #2 on: April 19, 2009, 08:04:55 PM »
You might want to look in to a step-down DC to DC converter, a lot less waste compared to the linear voltage regulators.

Offline klims

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Re: odd voltage and how to handle it?
« Reply #3 on: April 20, 2009, 02:52:51 AM »
It's not good practice to run linear voltage regulators in parallel. Apparently they 'fight' against each other.

Razor is right, linear voltage regs just waste power.
Look for switch mode devices. I'm successfully using a UBEC I bought on eBay to regulate my LiPo power down to 6v

Offline WizzardTopic starter

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Re: odd voltage and how to handle it?
« Reply #4 on: April 20, 2009, 09:32:32 AM »
I have looked at Switching Regulators such as the ones by dimension engineering and it seems very expensive to get one that will handle the amperage I think I need.

My Motors could possibly draw 14amps each when switching from full forward to full reverse (I think)

I might be looking at this wrong.

Do I need to have regulation that will handle the full possible total amperage draw from all components at once?

So I was looking for a less expensive solution. I can get the lm7806 voltage regulators that are rated at 1 amp each for .68$ if I get 10 or more.

Offline Soeren

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Re: odd voltage and how to handle it?
« Reply #5 on: April 20, 2009, 10:18:29 AM »
Hi,

I have access to a lot of surplus 7.5 volt radio battery packs. They put out about 8.5vdc when fully charged and I want to use them to supply power for my project.
[...]
Can I use some 7806 Voltage Regulators in parallel with a big Capacitor after them to drop the supply down for the axon, sensors, and the servos?

No, unfortunately you can not.
Your batteries are probably 6 cell NiMH (or NiCd).
Nickel-based cells are charged to close to 1.45V and is considered flat when they reach 0.9V if high discharge currents are used and 1.1V if low discharge currents are used (and something inbetween for currents inbetween).
That means that your batteries will vary in voltage from up to 8.7V freshly charged and down to 5.4V.
An 7806 needs 8.5 to 9V in to provide a regulated 6V out.

With a Low Drop Out (LDO) regulator, you can get by with a bit less than 6.5V at the input for 6V regulated out, but that is not really too helpfull.

As I see it, your best option is to select matching pairs of batteries to get the voltage in the range 10.8V to 17.4V and then use a switching regulator to get the low voltages you need. The motors can be run from a battery of their own, or switched down too for a more stable approach, but the motors won't care either way.

A place to start for cheap switchers is http://www.romanblack.com/smps/smps.htm


Any idea what amount of current the [...] I have not been able to find a data sheet for the ir sensors so if anyone has the current usage on them it would help [...]

Strange, that datasheet is all over the net. The GP2D12 has an average current dissipation of 33 mA (50mA max.).
http://www.google.com/search?hl=en&safe=off&rls=com.microsoft%3A*%3AIE-SearchBox&rlz=1I7GGLJ_en&num=100&q=GP2D12+filetype%3Apdf
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

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