Interesting USB charging behavior - the cables seem to matter.

This isn't really a quetion but more of an observation.

I have recently tried several different micro-USB cables to charge my 750i: Anker Powerline Micro USB cable, various micro-USB cables from various devices I've had over the years, and the Garmin cable that came with my 750i.

Apparently the Garmin cable is specified as a "2 amp" charging cable, which I've never seen specified in my other cables. In fact, the Garmin website specifically sells a micro usb cable only for the 700 series, whilst they have other micro usb cables for other devices.

The power supply is a high power SiC USB charger, with more than enough capacity to charge anything.

Most of the cables I have tried except for the Garmin USB cable will charge the unit (I know this because the charging icon and battery percentage appears on the screen) for approximately one to two minutes before the device simply shuts off. One other non-Garmin cable I tried charged for about 5 minutes / 8-10% before the unit shuts down.

When I use the Garmin 2 amp charging cable, the unit charges without any shutdowns.

I think the conclusion here is that while most people seem to be focused on the capacities of their charger, they should instead be much more focused on the capacity of their USB cable.

(I have a strong feeling that the Montana draws more than 500mA when charging via USB. I have measured the current draw when charging via the AMPs power cradle and it is closer to 700mA. I don't have a USB powermeter handy, but I think it would be useful if someone who has one could measure the current draw of the Montana when USB charging.)

0 twolpert over 2 years ago

I have never had any problem charging my 750i with ANY USB cable.

The USB device always controls the current draw during charging. There is a standard (if I ever knew them, I have forgotten the details) for sensing the capacity of the charger. Modern devices with some brains typically draw as much as they can handle based on what the charger can deliver. For example, I would expect the 7x0i to draw 500 mA from a standard USB port on a PC. Or up to 2A from a suitable wall wart or power bank.

0 2829612 over 2 years ago in reply to twolpert

You probably have a collection of better cables than I do just lying around

Garmin's own web site has a micro-usb cable specifically deisgned for charging the Montana 700/700i/750i:

https://www.garmin.com/en-US/p/pn/010-12978-00#devices

Oddly enough, all the other Garmin devices are not listed under the "compatible devices" section. At first I also thought all micro-usb cables were fungible, but this specific cable seemed curious to me. I'm guessing that it comes down to wire gauge.

My own experimentation seems to show that not all USB cables are alike. My only point is to offer that if someone does have a problem with charging their Montana unit, they try with a Garmin cable (or equivalent) first.

0 twolpert over 2 years ago in reply to 2829612

I have no idea what is magic about Garmin's "2A" charging cable. Makes no sense to me. Possible that it is heavier gauge wire than their ordinary cables.

The lack of compatibility with other devices (with the proper connectors) is like just an oversight on the web site. Not the first time for that.

I don't doubt that you see what you see. But I don't think it's normal. You might want to open a support ticket. To me, it sounds like the charging circuitry (specifically, the part that senses the capacity of the charger) might be defective.

0 twolpert over 2 years ago in reply to twolpert

I will admit that I do not own ANY charge-only USB cables. These typically come with chargers or power banks. I throw them away as soon as I get them. Just not worth the grief of getting them confused with a data transfer cable.

Edited to add: I don't see anything in the 7x0i release notes about f/w-related charging problems.

There has been some forum discussion about a possible hardware problem which causes the device to shut down at random times.

0 LEARNYEE over 2 years ago

this is my observation, the montana would draw up to about 1.5A, when it is power on or off and connected to a charger. also in some months before, I observed the following, which can be the problem with the USB cable or the USB charger can not provide the full 1.5A or the firmware itself:

1. When the Montana 700 is cradled and powered through cradle, it run at the full brightness, or at the brightness your set. Of course the internal beeper stop working at all.

2. When the Montana 700 is not installed at the cradle and battery powered, it can also run at full brightness, or at the brightness you set
2.1 If your brightness is set to max when battery powered and you connect to a USB power at this point of time, it will reduce the brightness of the unit. Sliding the brightness level up doesnt really increase the brightness, but lets slide it to the max

3. When the Montana 700 is cradled but not being powered by the cradle (for whatever reason, I think the fuse on my AMPS cradle was fried):
3.1 If it is not powered by the USB, it can run at the full brightness or any brightness you set. Internal beeper is working somehow.
3.2 If it is powered by USB, it will reduce the brightness to something like 60% for no whatever reason (the same brightness at point 2.1). Try this, boot up the Montana, set the brightness to max when it is running on battery, put it onto the cradle which is not powered, then plug in the USB power. On my unit, I will be able to observed that the brightness has been reduced. Press power button to call up the status page, leave it a while or start sliding the brightness slider, the unit would likely reboot itself, out of 10 times I try this, it rebooted 10 times.
3.3 now this is the other part of it, upon reboot, detach any usb power (but it is ok if it is sit in the unpowered cradle), press the power button to call up the status page, you can see the brightness is actually set at 60%, even it was set to max brightness when it is powered by the USB. Somehow if you are from point 2.1 and you restart the unit, you will observe this behaviour also.