Nuvi 750 Doesn't Get Power from AC Adapter

Did you happen to check the fuse for the cigarette lighter itself. I've replaced that fuse before on customer vehicles when their cell phone or other devices won't work.

In addition to checking the lighter's fuse- have you plugged it into another vehicle or another outlet in your vehicle.

Does the unit charge up and work if plugged in on a PC. If so the unit is fine and back to the plug/socket area.

I'll leave it to the tech's to explain how to check the adapter with a multi-tester.

Yes - The unit connects to the PC through the USB port. I have tried different vehicles' AC outlets without any positive results.

Even though the fuse looks good, I will replace it later today anyway and see what happens. Thank you,

You pretty much answered the problem being in the cigarette adapter, some cigarette adapters also have a fuse. As I recall the tip end unscrews, consealing fuse, try looking there.

Do you mean 12v DC? Few cars have AC.

Search for another recent thread at POI Factory about this. The opinion was that even if the cigarette lighter adapter and mount are working, and you drive long enough so the power is on a long time, the unit doesn't get charged as well as with the AC adapter that plugs in to the wall. The same goes for the USB cable to a turned-on computer - the current available is too low. Just yesterday I got a low battery warning on my nuvi 760, which had been in the car for a month. I plugged in the USB cable and it took 6 hours to charge fully based on the battery graphic.

Also, these units are getting old enough that their lithium-ion batteries may be failing. 2 - 3 years may be as long as they will work.

dobs108

My nuvi 255w charges at a maximum of 150ma no matter what the source of power. That includes a 5.7 volt ac/dc wallwart that I adapted by adding a USB socket to the wires, a Garmin cigar lighter adapter, and a Garmin USB cord to several PCs and laptops. All these will fully charge the 255w but the power has to remain of for a long time. Don’t forget your cigar lighter is probably not powered while the key is out of the ignition.

It is hard to imagine that a vehicle could not supply 150ma to the cigar lighter so I do not think low current is a factor.

If you tried other vehicles and it still didn't work with your cable, it is probably a broken wire, center adapter contact not touching the center of the lighter socket( I believe the contact on the adapter is spring loaded or terminal in your cable. Also if you still have your lighter element try it, if it heats up then your vehicle side is okay.

Evert, you are right about 150 ma being low current. I drive often, about 2 hours a day, and the cigarette lighter is then on. This is not enough for the 760. Every month or so I have to take it inside and charge it for a long time with the USB cable.

dobs108

From Garmins website:

"Garmin automotive devices will come with a charge out of the box. In most instances you will not need to charge before using. Your device will charge while attached to your 12V vehicle power cable.

In some cases your device may have lost a charge during shelf life. In this case you can charge these units in three ways:

Place unit on computer with USB cable for approximately 8-12 hours
Place unit on Garmin specified AC adaptor for approximately 4-6 hours
Place unit on 12V vehicle adaptor for approximately 4-6 hours

Your device should be fully charged after applying one of the steps from above.

*Charging of your device may be affected by extreme temperatures.
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Question: How do I charge my GPS unit?

There are three ways to charge the internal battery in your automotive GPS unit.

1. Use the provided vehicle power cable that came with your GPS unit. The unit will charge while powered on and using the device as well as when the GPS unit is powered off and plugged into a running vehicle.

2. Use an AC power adaptor. Some units come with this power cable to plug the GPS unit into a wall outlet allowing the GPS unit to take a charge. For units that do not come with this cable, one can be purchased from Garmin's online store.

3. For most units, the final way of charging the battery is to plug the GPS into a powered on computer with a USB cable. This method of charging will be a trickle charge and it may take longer than the other two options, however it will still charge the battery. A USB cable is provided with a few GPS models. For those that don't come with this cable, one can either be ordered from the online store or you can use a standard USB to mini-USB cable that fits the unit and plugs into your computer.

1 - Please note that temperature can play an effect on the charging of a device. If the battery registers a temperature of 0°C and below or 45°C and above (32°F and 113°F respectively) then it will not charge. When connected to external power it will only be operating off of external power.

2 - The Quest® and Quest® 2 will not charge using a USB cable."
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My 255W didn't come with an AC charger so I charge it 99% of the time in my truck. I've used it on several different occasions unpluged and the internal battery lasted several hours. From what I've observed, the unit can be fully charged from a vehicle charger.

Perhaps someone with specific technical knowledge in this field can confirm or deny all of the above.

Canuk, thanks for the comprehensive info. It confirms, from Garmin, that the GPS charges very slowly. Rdrivas probably has no problem with the power cord or mount - he needs to take it inside and charge it for a long time.

dobs108

I went to Best Buy and they checked and recommended a new car power cord that connects directly to the USB port on the unit itself, instead of the side of the socket, and it worked.

So I'm back in business. I appreciate all your replies and advice. Thank you!

I hope this works out for you. I am not sure if the 7x0 nuvi's are the same as the 7x5, but on the 7x5 you can't get full screen brightness when powering via the USB.

For what it's worth, I use the AC charger I have for my cel phone. As long as the tip matches the usb input on the GPS, it should work fine. Obviously not all chargers have the right tip, but mine works great.

The differences in the specs of the charger are primarily for the amount of current it transmits. I was concerned because they were different, but I researched it and found that it would be fine. Been doing it for a year with not issues at all.

The phone AC charger will charge the GPS (750) much more quickly than the computer's usb cord.

Ed Gcom, that is the best idea for charging. I also have a charger with the mini usb tip, so I will investigate the voltage and current before using it.

dobs108

I been using a Motorola cell charger to charge my Garmin for years and it works perfectly. I checked the voltage for my AC adapter before and it was safe for the Garmin.

AC charger ratings are output voltage plus amperage load.

1st
Compare gps charger, lets say it is 5vdc @ 500mA (1/2Amp), maximum amount of current this charger can handle
2nd
Compare to cell phone charger with same voltage output 5vdc
If amperage load on cell phone charger is 500 mA, 750mA (3/4A) or 1000mA (1.0A) using it is safe for the charger and gps use.

If less than 500mA best not to use that charger for gps use.

There is a bit more to it than just matching the physical size of the Garmin's USB mini socket. There are different sub-types of USB mini plugs that differ in how the ID pin (4) is used.

The mini-A ID pin is shorted to the ground pin (5). The mini-B ID pin floats i.e. is not connected to anything.

Charger manufacturers may use one of those and also may use various size resistors in a non-standard way to connect the ID pin to ground.

Garmin apparently uses the ID pin to determine what is being connected to the GPSr and adjusts the charging rate accordingly. I can see on my 255W and 285W diagnostic screens a reported “ID voltage” and that voltage varies according to the type of USB Mini plug I have inserted.

Also reported is the “USB Device”, which shows “USB Type-B when my Garmin USB cable (that I got with my Venture HC) is being used, and “Power Cable” when the cigar lighter socket adapter that came with my 255W is being used.

The Power Cable is rated 5 volts 1A (1000ma) and charges the 255W at a starting rate of 450ma, but charges the 285W at a starting rate of 536ma. Both rates taper off after a while. So even the same charging device may not charge different Garmins at the same rate.

I think that the ID pin on the USB Mini plug on the cigar socket adapter has a resistor to ground and the Garmin GPSr units use a voltage divider circuit to determine what the value is.

Question is, does the cell phone charger use the Mini-B plug, or do they use a resistor?

Also, if they use a resistor is it the same size resistor as Garmin uses and if not, how would the Garmin circuits react? What charging rate would it actually use?

Those questions can be answered by viewing the diagnostic screens on my Garmins, I don’t know if the 750 displays that screen.

As I've stated before, as have others, that my Motorola cell charger (500 ma) will not only charge the unit, but act in a way you can use the unit as a GPS at the same time.

I've even used it as a test with my power inverter in the vehicle. It works.

My Motorola charger puts out "5 volts at 850 ma" but it doesn't say whether it is AC or DC. It must be DC but I don't want to fry my 760 in an attempt to prove it. Evert's info on pin 4 makes me even more hesitant.

dobs108

My Garmins will do that with any wallwart I use that has 5 volts DC and at least about 200ma capacity. I just cut off any oddball plug that is on the cords and splice on the Mini-B end of readily available old camera cables.

Because the Mini-B plugs have a floating ID pin my Garmin nuvis first start up in “data mode” but after about 30 seconds they reboot into the normal use mode. Apparently after the short time of not seeing any activity on the two data lines, my Garmin nuvis decide that they are not connected to a computer and changes modes.

But of course they will only charge at the maximum rate of 150ma because of the Mini-B plug, so using any wallwart with greater than about 200ma this way would be kind of a waste, but I get lots of them free so that does not matter to me.

My favorite home brew charger is the one I made using a LG phone charger (AC/DC adapter rated 5volts 1000ma}. It had a flat connector I was able to open up and replace the insides with a USB-A socket that I salvaged from a USB-A extension cable.

With that socket, I can plug in any camera cable that has a Mini-B plug or can use the USB cable that came with my Garmin Venture HC (which also has a Mini-B plug)and then charge my nuvis.

So far the way I am using it I have to wait longer for the charge to complete but one of these days I am going measure the resistor on my Garmin cigar lighter charger and rig up a cable that will make better use of the higher current capacity.

If the charger cable has a USB Mini plug it is very unlikely that Motorola would put anything other than the USB standard 5 volt DC to pin 1(the power pin)of the plug.

Don't worry about the ID pin - the worst that could happen is your Garmin would go to the lower charge rate (150ma)instead of using the higher available capacity.