Power Cable Compatibility

[JBGarrity]

Until now, I've been using the cables that came with the products I've purchased for my rig. I recently bought a power bank that gives me a variety of cable options. I'd like to make good use of them.

The 12V DC cigarette plug that came with my Celestron AVX mount is too narrow for the power outlet on my Bluetti eb70 power bank. The loose connection is problematic and the exceptionally long cable is less than desirable. Several power cables that came with my various devices are too long. I've decided to find an alternative to the cigarette plug power cable since my power bank provides so many options. I also want to find shorter cables for my ASI cameras, ASIair Plus, dew heater ring, etc.

I've come to find that the amperage of the cables is indicated by markings on them. All of them show to be 18AWG. From what I can tell by looking at some of the online charts, is that an 18AWG cable is a 5A power cable. This would make sense since the Celestron AVX mount has power requirements of 3.5 amps. There is also the matter of 5.5mmx2.1mm cable types. Not being familiar with the specs and finding equivalents, leads me to several questions, since I've heard many comments on social media about cables becoming too hot, batteries overloading, and components smoking. All of which I would like to avoid.  😆

As far as I can tell, to avoid "cables becoming too hot", I need to make certain the amperage of the cable exceeds the amp draw of the device. Are there any problems or issues that arise from cables being well over the recommended amperage? For example, my AVX mount requires 3.5 amps yet the AC adapter Celestron provides is a 5amp power supply. Would a 10amp DC cable connected to my Bluetti's 10amp DC barrel plug output port be problematic in any way? Or let's say, I used 7A or 10A cables that exceeded the 18AWG/5A cables that are being used with the other products on my rig.

I'm trying to get the proper cable length as well as male 90-degree elbow barrel connectors at each end. I like that the cable that came with my mount has a lock screw on the barrel connector. It's a shame the cigarette plug is too narrow and the cable is so **** long. Ideally, if I could find a cable that is a 1.5 meter, 5.5mmx2.1mm, 18AWG/5A, 90-degree elbow barrel connectors, with a lock screw at one end, I'd have what I'm looking for.

Is there anything I do not understand about compatibility? Are there any alternative approaches that might work? Are there any online suppliers with a large selection of cable configurations? I'm having trouble finding the ideal cable management approach. Mostly because these cables don't fall off trees and I don't want to use cables that have been custom made for the applications.

Any insight you could share would be appreciated, thanks. 👍

Edited March 2 by JBGarrity

[Cosmic Geoff]

I can't give a complete answer, but would point out that the 'cigarette lighter' and the 5.5/2.1 connectors are both rubbish.  Industrial connectors would perform better, but would be troublesome to source and fit.

The AVX mount requires 3.5 amps? - that will be the current required for slewing at maximum speed. The current required for tracking will be far less.

A current rating for a cable is a guideline rather than a hard limit.  Common sense is required.  A cable that is adequate when completely unrolled might overheat when coiled on a drum.  A very long 18 AWG cable might give an excessive voltage drop, while an under-rated cable two metres long might not.

Specifiying a heavier grade cable (thicker, higher current rating) will cause no problems, except that it will cost more, weigh more, and be more difficult to handle.

[Geoff Lister]

I am a retired electronics engineer, so making up leads is easy to me.

The 18AWG cable has good current capacity for most astro equipment needs.

The other thing to consider is volts-drop along the cable. Some of the Skywatcher equipment (particularly Synscan handsets) is sensitive to lowered voltages at its end of the lead chain. This is where the lead lengh, and its related resistance, is important. The table that I looked at, showed 18AWG resistance as 20.9 ohms for 1000 metres. That equates to a volts drop (with supply and return wires, and the 3.5A mentioned above) of about 0.15V per meter of cable length. If you assume 10 milliohms contact resistance for each (clean) connection in your connectors at each end of the lead, 4 * 0.01 *3.5 = 0.14V will be added to the drop, independent of lead length.

I think that, given a good 12V supply, most equipment that requires 12V will be OK with 1.5 metres of your 18AWG cable.

Geoff

[JBGarrity]

4 hours ago, Cosmic Geoff said:

A current rating for a cable is a guideline rather than a hard limit.  Common sense is required.  A cable that is adequate when completely unrolled might overheat when coiled on a drum.  A very long 18 AWG cable might give an excessive voltage drop, while an under-rated cable two metres long might not.

Specifiying a heavier grade cable (thicker, higher current rating) will cause no problems, except that it will cost more, weigh more, and be more difficult to handle.

Thanks for the reply.

What you've said about there being "no hard limit", explains why I've seen comments in Google searches that have multiple exceptions to the rule. I intend to match my current cable specs to the new shorter cables I'll eventually purchase. Fortunately, my objective is to shorten not lengthen the cables, which should avoid the cables being too long or bundled/coiled together.

It's good to know that a "thicker, higher current rating" wont be an issue. Cheers. 🍻

[JBGarrity]

4 hours ago, Geoff Lister said:

I think that, given a good 12V supply, most equipment that requires 12V will be OK with 1.5 metres of your 18AWG cable.

Geoff

Thanks for the reply.

It's good to hear this from someone who has professional knowledge. I've heard conflicting and contradictory information on the internet from multiple discussions in my Google searches. It's why I chose to register and post to an Astrophotography group.

Appreciate the help.

[Geoff Lister]

A warm welcome to SGL. We like to help with advice where we can. There is no such thing as a stupid question.

Geoff

[adyj1]

6 hours ago, Cosmic Geoff said:

but would point out that the 'cigarette lighter' and the 5.5/2.1 connectors are both rubbish.

Can I ask why the DC 5521 barrel connectors aren't considered to be adequate?

I got rid of any cigarette lighter connectors on my cables and toyed with using two-pin GX12 aviation connecters - but decided to stick with the 5521's as the centre-positive wiring is a common standard and I'd never had any problems with them. 

Ady

[Cosmic Geoff]

13 minutes ago, adyj1 said:

Can I ask why the DC 5521 barrel connectors aren't considered to be adequate?

I got rid of any cigarette lighter connectors on my cables and toyed with using two-pin GX12 aviation connecters - but decided to stick with the 5521's as the centre-positive wiring is a common standard and I'd never had any problems with them. 

I have several mounts where the power is fed in via a 5.5/2.1 connector, and each of them have proved prone to intermittent connections if the plug is touched or disturbed, which loses the GoTo alignment. As I wrote above, rubbish.  Fettling the split center pin helps, but only temporarily.  Providing a cable restraint next to the plug also helps.

[Geoff Lister]

I think that the main problem with these 5.5/2.1 mm connectors is that the plug, with its 2 metal cylinders is ok, but the equipment side, with centre pin and cantilevered spring side contact provides poor electrical contact and very poor (as mentioned above) plug retention. I have added a cable retention clip on most of my mounts that use these connectors.

Geoff