Can electronic device be run right to low voltage?

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  #1  
Old 07-25-11, 06:14 PM
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Can electronic device be run right to low voltage?

Battery in my GPS died so I have to order another 3.7 volt battery.
Wanted to use the GPS so I rigged 12 volts to my auto inverter and then ran my GPS thru the 120 volt cord.
GPS shut down and just before thatthe green power lite on the inverter was flashing then went off.
I read that the inverter has a auto shut off at 10 volts to protect the auto battery from being run down to a no start condiion.
My question is: Can an electronic device be run right down in voltage until it stops to operate with no damage?
 
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Old 07-25-11, 06:48 PM
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Is this a pure sine wave or a square wave? Electronic wallwarts shouldnt be run on a square wave.
 
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Old 07-25-11, 07:38 PM
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Wanted to use the GPS so I rigged 12 volts to my auto inverter and then ran my GPS thru the 120 volt cord.
Do you mean you have a 120v AC input on the GPS?
 
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Old 07-26-11, 02:45 AM
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Originally Posted by ray2047 View Post
Do you mean you have a 120v AC input on the GPS?
It is a Magellan 400 Explorist with a built in battery or it can be plugged in to AC
 
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Old 07-26-11, 02:48 AM
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Originally Posted by Justin Smith View Post
Is this a pure sine wave or a square wave? Electronic wallwarts shouldnt be run on a square wave.
It cost $12 so I would guess square. I dont know what a wallwart is.
 
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Old 07-26-11, 05:08 AM
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Originally Posted by frankiee View Post
It cost $12 so I would guess square. I dont know what a wallwart is.
That cheap is definitely square wave. A wallwart is an AC adapter with prongs sticking out of it that plugs right into an outlet - the ones that take up two or three spots on a power strip (so named because they bump out of the wall like a wart when plugged in).

I have to ask, how did you rig this inverter up? Did you do it for use in the car (plugged into the cigarette lighter or power port) or for hiking (12v battery in a backpack)?
 

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Old 07-26-11, 08:47 AM
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I'm not clear what the question is? Are you worried about the GPS unit being damaged from having been run off the inverter?
 
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Old 07-26-11, 09:59 AM
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I'm not clear what the question is? Are you worried about the GPS unit being damaged from having been run off the inverter?
It sounds to me like he was wondering if he can use the gps until the inverter shuts down due to low battery.
 
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Old 07-28-11, 09:55 PM
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Originally Posted by JerseyMatt View Post
I have to ask, how did you rig this inverter up? or for hiking (12v battery in a backpack)?
I put 8 AA batteries in series and connected them to a "female" cigarette lighter receptical. Then plugged in my inverter and had the AC transformer of the GPS plugged into that. Put that creation into my backback and went riding bike.
I am now wondering if I can just run it off 2 AA batteries. That would be 3 volts instead of the original 3.7 volts DC. Or would it run at all. Is there a point in electronics that the low voltage will damage the unit?
This was the reason for the question. Sorry for being vauge.
 
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Old 07-28-11, 11:40 PM
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Ahhh I see. 8 AA's don't have enough capacity to run that inverter for any amount of time. And for what you're doing (12vdc > 120vac > 3.7vdc), it's incredibly inefficient. 3.7v is a lithium-ion voltage, and to charge usually takes 5v. Approx 2.5v would be where the device considers the battery dead, so that's only slightly less than what two AA's put out. So take a look at the AC charger.. Is the output voltage 3.7v or 5v? And what kind of plug is at the GPS end? Is it like the barrel connector with the pin in the middle or is it mini-USB (like on a digital camera)? Depending on your answers there may be a few options available.
 
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Old 07-30-11, 05:05 PM
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Most electronic devices have a generous range of voltages in which they will operate. The unit is protected from undervoltage and will just shut itself off when the voltage reaches the threshold. (3 volts? 2.7 volts?) Overvoltage is another story. 5 volts may damage the unit. 12 will probably kill it.

However, since your device needs 3.7 volts you could series-wire 3 AA rechargeable NiMH. Each NiMH has a nominal voltage of 1.25, so the total would be 3.75. If you need more capacity use D-cell NiMH (up to ten times the milliamp hours of an AA) or wire a couple of the AA series-wired 3-packs in parallel with each other.

If you go this route, recharge the batteries individually (not wired in series).
 
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Old 07-31-11, 09:49 AM
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Thanks for your help people. I did find a used GPS that uses 2 AA batteries for $40. Thats the cost of a new 3.7 LiON battery
So I am up and biking (I use GPS to record average speed etc for bicycle training) with the new to me GPS. I can order another battery for the other GPS in my liesure now.
I acually made that contraption for my 1st GPS as part of an experiment. With 8 AA's I did think it would run longer then the 40 minutes that it did run. The inverter must be the inefficient part I think because I thought transformers were near 100% effecient. The run time for the used Magellan Triton 300 is stated to be 10 hours on the 2 AA batteries.

Thanks again
Frank
 
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Old 07-31-11, 10:11 AM
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Use to you could get a bike powered light that used a generator driven by the wheel. You might be able to mount one of those minus the light and a rechargeable battery so you always have power for the GPS. Bit more drag when biking but hey, you said you were training.
 
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Old 07-31-11, 11:05 AM
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I'm certainly no expert on the matter, but the efficiency of the transformer might not be as close to 100% as you think. I took a quick gander on Wikipedia to see what I could find and they seem to say that the large transformers used for electrical grids are the most efficient at about 98%. They also say that the materials to make then that efficient require more expensive materials. Based on that, I would expect transformers in consumer grade electronics to be less efficient. They also throw off a lot of heat too.
 
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Old 07-31-11, 11:24 AM
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The inverters actually use dc-dc power supply and then switch it to ac.
 
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