Solar LiPo charger and display meters

[DVCnerfherder]

I'm getting ready to assemble my Mintyboost and Solar LiPo charger kits and would like to pimp them out with a couple of meters. I'd like to add a volt meter to measure the battery voltage while a device is charging but I'd prefer that it not be powered if there's no load on the charger. I could wire in a switch to turn off the display, but could I use a 3-wire volt meter (ID 705), connect the power leads to GND and LOAD and the third wire to BATT? That way, if there's no load there's no power to the meter and it won't drain the battery.

I'm also planning on using this quite a bit over the summer and would like to connect a temperature meter but only want to have it display while the battery is charging (i.e. when the unit is out in the sun). Again, I could simply connect it to +5V and GND with a switch (again, so as to not drain the battery when it's not charging), but I was wondering if I could I connect the sensor to DC IN and STAT1 (instead of or in parallel with an orange LED) to have it display only while charging. Since the temp meter (ID 576) requires a minimum of 4.5V to run it wouldn't function (and again, drain the battery) in a low battery condition.

Will these work or am I completely out to lunch? It's been a long while since I've dabbled in electronics. Thanks.

[john444]

Hi DC,

The 3-wire volt-meters are some nice little meters.
Also, I believe they will almost but not quite work without modification.
There are two problems.

The big one is that they may stop working below 4.5-V.
(Although, mine works @ 3.8-V)
Since the charger pulls the solar-panel voltage down when it is drawing
current to charge the LiPo, there will not be more than 4.5-V to
power the meter. Although, by adding a diode or two between the
solar panel and the charger, the available voltage on the solar-cell will be
high enough to power the meter when there is enough sunlight.
The meter will steal 3 to 4-mA but you will probably not notice the loss
when there is enough sunlight to charge your LiPo.

The other problem is that the meter does not have a very high
input resistance. The meter will put a slight (~10-uA) but continuous
drain on the battery even when the meter is not powered.

A bigger problem for me was that the meter does not have a bezel
so it is somewhat difficult to mount.

Good Luck with your project.
Would love to see it as you go along,
John

[Roliideowly]

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