laptop output voltage

[raymo]

Can someone tell me what voltage my laptop puts out when in powered off mode. My tracker runs on 3 AA batteries [so max around 4.8v when batteries are fully charged], and stays at ambient temp, but when running off my laptop it gets hot, so I assume that something is wrong.
raymo

[Startrek (Martin)]

Raymo

If your laptop is powered off there will be no voltage at your USB ports for charging or other requirements ( unless yours is different? )
Once powered on the USB ports provide the following -
USB2 5V DC max 500mA or 0.5 amp
USB3 5V DC max 900mA or 0.9 amp

I assume these specs are for continuous rated load not transient load caused by a motor or transformer or the like

Nano tracker has a stepper motor but do not know it’s current draw as the voltage would fluctuate between 3.5 to 4.8 volts during operation
Don’t know if this helps at all
Cheers

[raymo]

Thanks Martin, my laptop, like many newer models has power off charging which is only available at one of the four USB outllets, and is a different colour to the other three. I had assumed it would put out 5v, but I can't understand why the tracker gets hot since 5v is only about 5% more than what it is normally subjected to.
raymo

[Startrek (Martin)]

Raymo
How long is the USB cord from laptop to tracker ?
Remember we are only running 4.8 volts DC not 12 or 24
Could be voltage drop in the cable if it’s longer than 1 or 2 metres. USB charger cords are usually only 1 metre long
A long cable will increase the current draw and cause some heat especially at extra low voltage
Cheers

[raymo]

The cable is about 900mm long, but as no cable for external power supply
is supplied with the tracker, I am using the cable that is used to transfer
images from the camera to my laptop, as the connection happens to be the same.It just occurred to me that maybe the cable is too thin, causing voltage drop, after all I imagine a cable used for transferring images wouldn't need to be able to carry much current.
I have just had a look at the tracker, and the power requirement is 4.5v @ 0.4amp.
I'll see if I can get a normal micro USB cable and see if that changes anything.
raymo

[sil (Steve)]

Could be your tracker isn't designed to work with the different voltages and amps of rechargable batteries. Some products burn out fast if you do not use alkaline as they were designed to use. Rechargable AA does not equal alkaline AA batteries. The purpose of the laptop power via usb when off is to charge your phone which is designed to suck power especially when its pushed fast. I just dont think your gear is designed to work the way you want and its lucky the tracker still works.

[redbeard (Damien)]

Hi Raymo,

Standard AA batteries are 1.5 volts.
Rechargable AA batteries are 1.2 volts.
USB Standard for all USB ports is 5 volts.

If you are using rechargable AA's, then the output voltage for your unit will be 3.6 volts.
That is well below 5 volts from the USB port and might explain why things are getting hot.

If you are getting voltage drop, then that would actually be in your favour as the voltage is too high in the first place. Unless the voltage drop is ridiculously low.

As Sil mentioned, your unit may not like different voltages. Most devices need to operate at their rated operating voltage. As for current, they will only draw what they need.

Cheers,
Damien.

[raymo]

Thanks everybody. The tracker is rated to work from 3.6v to 4.5v.
I used to use 3 AAs =4.5v, never rechargeables, then switched to the laptop as a power source. I used the cable that is used to transfer images from the camera to a laptop because the sockets on the laptop and tracker matched the USB and apparently Mini USB fittings on the cable, however on closer
inspection I have discovered that the plug and socket at the tracker end of the cable whilst superficially the same are in fact different internally, so I think that is the problem; the moral of the story is to never assume anything.
I'll get a new Mini USB cable and see if that fixes the problem.
Incidentally, this is the later model that is designed to run on rechargeables,
alkalines, or an external 4.5v power source; the previous model was not
equipped for external power. Yes I am lucky that it still works.
Thanks again.

[Startrek (Martin)]

Raymo

Glad your getting to the bottom of your power / charging issue
Next clear night , more wide field images please , we don’t see enough of them
Clear Skies
Martin

[raymo]

Hi Martin, am away from home adjacent to the big smoke and its
attendant light pollution, plus bright moon, so will be a bit of a delay
before resuming imaging.
raymo

[raymo]

I now definitely have the right cable, but the tracker is warm in two minutes,
very warm in four, and hot in 6-7 minutes, but still only faintly warm when running on 3 xAA, even after several hours. Barely detectable by the hand,
easier if put to the lips. Oh well, back to batteries.
raymo