12v Power Pack - HEQ5 Pro

[Mr_Smith]

Hi, I use a HEQ5 Pro powered from the mains and it works perfectly but when I try to power it from my Skywatcher power pack cigar lighter socket it blows the fuse in the lead. It works ok via the USB port but not from the 12v cigar socket. Any ideas how to get this to work? 
 

The output on the cigar socket is 12v 10amp. 
 

Regards

Gray 

[wulfrun]

First off, do you have or have access to a multimeter? It'll be pretty indispensable to have one and you don't need an expensive, all-singing one.

Are you sure the lead delivers the correct polarity? When exactly did the fuse blow? Was it when you plugged it into the power pack, when you plugged the other end into the mount or only when you switched the mount on? What's the rating marked on the blown fuse? (Not what it should be, but what it actually is).

You need to troubleshoot methodically to find the fault and the first thing to note is NOT to keep replacing the fuse and blowing it again, you may well do (more) damage.

[Mr_Smith]

Thank you, I do have a multimeter. The fuse blew as soon as I turned the power pack on. The fuse that blew was 5amp 

[wulfrun]

9 minutes ago, Mr_Smith said:

Thank you, I do have a multimeter. The fuse blew as soon as I turned the power pack on. The fuse that blew was 5amp 

OK, so everything was connected up before switching on at the powerpack? I'm not familiar with the mount, it'll have a rating marked on it...is a 5A fuse enough (I'm guessing it's plenty)?

Use your test meter to check the lead first of all then. Continuity along both conductors, the polarity can be verified and no short between the conductors. If that checks OK, replace the fuse, plug the lead in and don't connect the other end to the mount. Switch the powerpack on and the fuse shouldn't blow. If all's well up to then, the fault is in the mount as some disassembly will be needed but let's see.

 

[Mr_Smith]

So I’m guessing the 10amp output was too much. I always thought that the mount would only draw the amount of amps that it needed though. Or am I completely wrong? 

[Mr_Smith]

Just checked the continuity, all is good. 

[Mr_Smith]

Just checked the continuity, all is good. The lead is now plugged into the power pack and it’s staying ‘on’ as in powered. 

[Mr_Smith]

What baffles me is that it’s a Skywatcher power pack and a Skywatcher mount. Surely they should be compatible right? 

[wulfrun]

22 minutes ago, Mr_Smith said:

So I’m guessing the 10amp output was too much. I always thought that the mount would only draw the amount of amps that it needed though. Or am I completely wrong? 

No, you're completely right, the mount draws what it needs (provided there's an edequate supply).

[Mr_Smith]

1 minute ago, wulfrun said:

No, you're completely right, the mount draws what it needs (provided there's an edequate supply).

Thank you. This is baffling me…

[wulfrun]

Next step would be to take meter readings on the mount then (no power applied). Use the Ohms range and test both ways with the meter leads. If you can't easily get at the mount socket terminals, use your lead and test the cigar-end. Just to repeat...the powerpack is NOT used or connected at all for this bit.

[Mr_Smith]

13 minutes ago, wulfrun said:

Next step would be to take meter readings on the mount then (no power applied). Use the Ohms range and test both ways with the meter leads. If you can't easily get at the mount socket terminals, use your lead and test the cigar-end. Just to repeat...the powerpack is NOT used or connected at all for this bit.

Just done that and got readings both ways. 

[wulfrun]

OK, kind of not unexpected. Next step is to get at the power leads inside the mount and trace back then. Once inside I'd expect an obvious short somewhere since you know the mount works. Sadly, it's not my area of knowledge and you'll have to wait for someone else to guide you on it. Before doing so, just double-check if the fault is present with mount switched OFF as well as ON. If it's still there with the mount OFF it pretty much narrows it down to the mount's power socket itself.

If you power it from mains, are you still using the same 12V socket on the mount? Just realised that that would be puzzling if it works OK that way.

[Mr_Smith]

32 minutes ago, wulfrun said:

OK, kind of not unexpected. Next step is to get at the power leads inside the mount and trace back then. Once inside I'd expect an obvious short somewhere since you know the mount works. Sadly, it's not my area of knowledge and you'll have to wait for someone else to guide you on it. Before doing so, just double-check if the fault is present with mount switched OFF as well as ON. If it's still there with the mount OFF it pretty much narrows it down to the mount's power socket itself.

If you power it from mains, are you still using the same 12V socket on the mount? Just realised that that would be puzzling if it works OK that way.

I am using the same lead when running it on mains power and plugged into the same socket on the mount. 

[Mr_Smith]

The battery pack output is 12.4v, I’ve tested it. 

[wulfrun]

Ah OK, that adds to the confusion then! If the mains power supply works fine, then the mount must be OK with no power shorts. No need to start messing there. In that case, logically the 5A fuse is inadequate. It's not unusual for electronics to have a current-surge at power-on but I'd be very wary of just upping the fuse rating.

What exact type of fuse is the one that blew? Is it definitely the recommended fuse?

[Mr_Smith]

30 minutes ago, wulfrun said:

Ah OK, that adds to the confusion then! If the mains power supply works fine, then the mount must be OK with no power shorts. No need to start messing there. In that case, logically the 5A fuse is inadequate. It's not unusual for electronics to have a current-surge at power-on but I'd be very wary of just upping the fuse rating.

What exact type of fuse is the one that blew? Is it definitely the recommended fuse?

It was the same as this one…. 12v 5amp 

[Carbon Brush]

Do you still have the blown fuse?
If so, can you read the numbers and letters from the end caps?

 

[Mr_Smith]

I’ve just tried this 12v air compressor in the battery pack and it worked fine.

[Mr_Smith]

5 minutes ago, Carbon Brush said:

Do you still have the blown fuse?
If so, can you read the numbers and letters from the end caps?

 

F5AL250V

[wulfrun]

7 minutes ago, Mr_Smith said:

F5AL250V

It's a quick-blow fuse. I was about to ask what was on it but beaten by @Carbon Brush

The F means fast, so it blows quickly on any surge/overload. I'd get a slow-blow/anti-surge type, it'll be marked T5A not F5A.

EDIT: we may have found the problem!

Edited September 3, 2022 by wulfrun

[Carbon Brush]

@wulfrun. Simultaneous typing 😁

OK you have a quick blow (F for fast acting) 5Amp fuse. with 250V rating.

If you fit a fuse with a 'T' rating, rather than 'F' the probability of blowing on surge is much lower.
In this application, the fuse is there to protect against damage (or fire) if there is a short circuit.
If the fuse takes a fraction of a second longer to trip, it doesn't matter.

Usually shorts are in the leads or connectors, allowing quite high fault current.

A battery pack (using led acid) will deliver >100A into a short circuit, or when delivering inrush to a mount.
Depending on design, a mains PSU may current limit at 150% or so rating, making fuse failure less likely.

HTH, David.

[Mr_Smith]

You guys are amazing. I’ll search Amazon and get some T rated fuses ordered. Fingers crossed this is the problem. Once they arrive I’ll test it all and report back. 
 

Oh……thank you all very much. 

[Clarkey]

To be honest you shouldn't get close to 5 amp from the HEQ5. My total imaging rig only draws about 3 amps.

I have run my heq5 on this power pack without issue so there is no reason why it shouldn't work.

Was it the fuse in the power pack or the cable?

[Carbon Brush]

@Mr_Smith You are very welcome. Happy to help.

@Clarkey The problem here is inrush, not steady stste current.
Most mounts have an inrush current at power up. How high, and for how long, depends on the mount.
Most will contain a large-ish electrolytic capacitor. Some may momentarily energise motors until the controls 'wake up' after a fraction of a second.
Either condition will place stress on a fast acting fuse.
You can demonstrate this for yourself by having a lead acid battery and an exposed fuse. Then connect a load with inrush. A large capacitor is good.
At power up you may see the fuse wire momentarily sag as it heats. In extreme you can pick up a momentary red glow.
The fuse is still OK. But after a few dozen operations like this is fatigues and fails.

Fast acting fuses cost a little less (pennies) than time delay models so often find their way into the wrong applications.
You sometimes see cheapie stuff from China that fails on inrush. Easy enough if the fuse is accessible. But sometimes it is internal.
Then there is the stuff with fake fuses - but I am wandering off topic.

HTH, David.