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Old 04-23-2012, 07:11 PM   #1
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voltage drop


Hello All,
Hopefully I am posting this in the correct forum!
I am new to the forum and I have a question I would like to pose.
I am trying to make an extension cable for my telescope hand control.
I have had good results with the 25' length but it is to short . So I made another one 50' in length but it give me connection error codes. The cable is correct as it worked for a while .I am using an rj12 6pin connector with cat5 cable(24awg). The power supply is 12V DC with 2.5 amps running on house AC.
The question is: If I put a different power supply on that is 12v DC using 5.0 amps will the increase in amperage effect the DC current flow?

Thanks,
Don

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Old 04-23-2012, 07:31 PM   #2
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I have had good results with the 25' length but it is to short . So I made another one 50' in length but it give me connection error codes. The cable is correct as it worked for a while .I am using an rj12 6pin connector with cat5 cable(24awg). The power supply is 12V DC with 2.5 amps running on house AC.
The question is: If I put a different power supply on that is 12v DC using 5.0 amps will the increase in amperage effect the DC current flow?

Thanks,
Don
Substituting a bigger power supply more amperes capability will accomplish nothing regards voltage drop on a longer length of wire.

You need heavier wire for the longer distance of 12 volt run. Now if you can run 120 volts closer to where the telescope is so the 12 volt line is much shorter then you will not have the voltage drop problem.

For the same piece of wire the number of volts dropped (lost) is the same for a given number of amperes regardless of the voltage. Losing 3 volts out of 120 almost never causes a problem while losing 3 volts out of 12 almost always causes a problem.

For electronic equipment do not try to use a higher voltage power supply given the distance to overcome voltage drop problems. The voltage will vary as the equipment amperes draw varies and can burn out the equipment.

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Last edited by AllanJ; 04-23-2012 at 07:36 PM.
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Old 04-23-2012, 08:12 PM   #3
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You can also set up a battery cart with a deep cycle battery to power, if you are using the telescope in places that you may not have access to power (ie unable to drive your car or truck out there, or unable to pull a 120vac leg outside.).
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Old 04-24-2012, 02:01 AM   #4
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Try Cat 6 cable. It uses 22 AWG wire....the voltage drop will be less.
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Old 04-24-2012, 05:43 AM   #5
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Try Cat 6 cable. It uses 22 AWG wire....the voltage drop will be less.
This sounds like something good to try. You mentioned "connection error codes" so there is a possibility that the DC voltage drop isn't your problem. Do you know which protocol your controller uses? If it is unbalanced RS-232 you may be getting close to the maximum length and the larger wire might help in this case also.
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Old 04-24-2012, 08:22 AM   #6
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An added thought if you have enough spare wires and are good at soldering and working with small wires. It's a little hackish but you could double up on your important wires right behind the RJ connector but only connect with the mating twist. Two each for power and ground if voltage drop is your problem. If you are having comm errors and it is an unbalanced protocol then doubling up with the same twist will help that issue as well. Twisted wire is not the best to use with an unbalanced circuit but doubling up will essentially make it act like a single wire.

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