Power Consumption

[idahowayne]

Am trying to decide between the OBi 100 and the OBi 200. We live off grid (solar power only) so I will be running the OBi straight from 12 volts without the power adapter.

I have been told that the OBi100 draws 95 milliamps at idle and 150 milliamps while talking. I would like to know what the 200 draws for comparison. If it is the same or close I would prefer the 200.
Thanks in advance for any info you can provide.

[sailing]

I cannot help you with the current draw from these devices but I have some recommendations for you. The 12V must be regulated. The Obi expects 12V not 14-15V lead acid batteries could supply. Also, you need a fuse in series with the 12V to the Obi for your setup. There must be a way to limit the current should some kind of short occur in the Obi.

[OBiSupport]

OBi200 needs 110-120 milliamps while idle and 160 milliamps while talking.

[idahowayne]

Thank you support. How about the 202, does it draw any more current than the 200?

[Jackson]

The 12V must be regulated. The Obi expects 12V not 14-15V lead acid batteries could supply. Also, you need a fuse in series with the 12V to the Obi for your setup. There must be a way to limit the current should some kind of short occur in the Obi.

Would this simple approach work?  12V zeners are quite inexpensive.

http://www.learningaboutelectronics.com/Articles/Overvoltage-protection-circuit.php

[OBiSupport]

Thank you support. How about the 202, does it draw any more current than the 200?

When it comes to power consumption, the OBi202 is almost identical to the OBi200.  OBi200 needs 110-120 milliamps while idle and 160 milliamps while talking.  If there is a second simultaneous call on the other phone port of the OBi202, then the consumption will increase by a proportionate amount.

[Shale]

Would this simple approach work?  12V zeners are quite inexpensive.

http://www.learningaboutelectronics.com/Articles/Overvoltage-protection-circuit.php

No. That circuit presumes a power supply whose voltage is less than the zener point, and the zener is only absorbing short overvoltage spikes.

When a zener diode used as a regulator, there needs to be a resistor in series with the power source. That type of regulator is very inefficient. Instead you would want to use a low-dropout regulator.

[sailing]

Jackson, in addition to what Shale said, the circuit you linked to is for overvoltage protection. That circuit is for if the voltage goes over the zener voltage, the fuse will open. A zener requires a properly chosen resistor in front of it so the zener will regulate the voltage by shunting the current through the resistor.

Since idahowayne is so concerned about energy consumption, a linear regulator is still the wrong approach. There are dc/dc converters with efficiencies of 98% no matter what the input voltage is. You can find them at Digikey, Mouser or Newark Electronics.

A linear regulator regulating an input voltage of say 15V must drop 3V at 110ma to dissipate 0.33 watts. It isn't much but when running off grid, every watt reduces the run time of the battery.

[dircom]

I assume, over/under dc/dc voltage regulators use more energy, the farther the presented voltage is from the target voltage?
ie, 9vdc -> 12 volts uses less power than say 18vdc -> 12 vdc?
or 14vdc -> 12vdc uses less power than 18vdc -> 12vdc?

[sailing]

dircom, The efficiency ratings will not change for the voltage ranges you gave. In fact, there are dc/dc converters that will maintain 98% efficiency stepping 56V to 12V. The losses aren't in dropping the voltage. These converters chop the voltage at high frequency then pass them through a transformer to step down the voltage. The losses are in the chopping process which doesn't change much over the voltages we are talking about.

[idahowayne]

Sailing, Thanks for all the info. I have some DC to DC converters and plan to use one to keep my 24 volts down to 12 for the OBi.
I have read that DC to DC converters are not reliable at around  10% or less that their rated output and can produce voltage as much as double what they are set for. The OBi draws about 110 milliamps and I have not seen any converters that small. Any ideas?

[sailing]

The output voltage will always regulate no matter what the output load is. Efficiency may suffer a few percent at light load but think about the power you are using and the extra few percent of loss. It ain't much. You will want an isolated output so the Obi's ground isn't part of the rest of your system otherwise you may create other problems.

XP Power is one manufacturer. There are many others.
http://www.xppower.com/EN/DC-DC

You can order XP's converters from
http://www.newark.com.