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   Home   Help Search  
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Author Topic: looking for help on amp-volt meter readout  (Read 6151 times)

Posts: 15

« on: September 18, 2012, 01:48:55 PM »

I am trying to find a source for anything on building a amp/volt meter to watch my battery charger and battery usage I guess it is. I like to just watch my batteries with a/v at same time not 1 meter for each.

I have some LCD screens 4 line modules I like to use if anyone can help me with a diagram parts list a website suggestions anything at all.


New to home brew ! please help a guy out some.  OH I do have pic programmer well my son does and if needed to go that way I can do so also.


Posts: 545

« Reply #1 on: September 18, 2012, 04:16:00 PM »

There are quite a few dual units on ebay; a search for "digital volt amp meter" produced ones like this;

This is just an example; there are others of various kinds.

Posts: 15

« Reply #2 on: September 18, 2012, 06:59:44 PM »

Yes but what I need is a way to monitor the AH used and amps in etc. so I do not over charge or over use the battery bank. I saw these meters but they will NOT do everything needed so what I am needing to go with a unit like this is a schematic to build the complete unit to verify more then 1 source I guess i am trying to do. like input to battery and output from battery so I know I do not over use it and burn it out.

I am not sure how to explain it fully in techie terms. I know in my head but have trouble putting it on p[aper. (disabled ham here)

what I will need is maybe 2 or 3 of these to monitor each battery in and output Huh or how would you suggest to do this ?


Posts: 5482


« Reply #3 on: September 18, 2012, 07:26:57 PM »

what I need is a way to monitor the AH used and amps in etc. so I do not over charge or over use the battery bank.

Whatever you're using to charge the battery should take care of the "Ah in" part.

As far as "Ah used", do you need just state of charge or do you care exactly how many Ah you've used?  I ask this because how many Ah you get out will depend a lot on how much current draw there is.

For a simple SOC meter, an expanded scale voltmeter will tell you a lot, and is "passive" (just connect and read):

Curtis instruments makes several models of electric "fuel" gauge instruments that will tell you predicted state of charge.  If you want detailed battery stats, anything from a "Watt's Up" unit, an E-Xpert Pro battery gauge to solar system battery bank monitors to DIY DAQ on a PC are all possibilities.

how would you suggest to do this ?

Do...what?  What do you want to monitor and how accurate does it need to be?

Mark K5LXP
Albuquerque, NM
« Last Edit: September 18, 2012, 07:48:53 PM by K5LXP » Logged

Posts: 2409

« Reply #4 on: September 18, 2012, 10:22:30 PM »

As you are new to homebrew this may not be a good project to start with.
Anyway at the guy offers to send his circuit design.
If you really want to do this design by yourself you need to measure voltage, current and time for incoming and outgoing, Mathematical calculation is a matter of programming the PIC. Depending upon the batteries, of course, there is a factor to be applied for losses, i.e. not all charge can be obtained on discharge.

Posts: 1265

« Reply #5 on: September 18, 2012, 11:40:15 PM »

Get a hydrometer, that is the best indication of the state of charge of a LA battery.

ex MN Radio Officer, Portishead Radio GKA, BT Radio Amateur Morse Tester.  Licensed as G3YCP ZL1DAB, now taken over my father (sk) call as ZL1BBW.

Posts: 1460


« Reply #6 on: September 19, 2012, 09:00:41 AM »

Not cheap but pg 22 of the Oct 2012 QST shows a very interesting device.


Posts: 14491

« Reply #7 on: September 19, 2012, 09:20:09 AM »

It is quite possible to monitor total AH used by monitoring current over time (for example, using a microcontroller). The problems is, what are you going to compare it to. The rated AH capacity of any battery is not necessarily the AH capacity that it can provide in your application. The rated capacity is at some specified constant current draw until some terminal voltage (like 10V) is reached. If you draw more or less current then the available AH capacity changes. Most radios stop working somewhere around 11.5V which means that the remaining specified capacity is not available to you.

A two-state or three-state charger will take care of making sure you battery is fully recharged. I'd use a simple voltmeter to monitor battery usage because it is the minimum operating voltage of the radio that will be the limiting factor rather than the specified terminal voltage of the battery. Typically once the battery voltage drops much below 11.5V under full transmitter load you will be done, in spite of the fact that the battery may have some AHs left to provide at a lower voltage.


Bob  AA4PB
Garrisonville, VA

Posts: 2409

« Reply #8 on: September 19, 2012, 10:28:57 AM »

I thought this was about DIY.
A commercial unit would be:

Posts: 2085

« Reply #9 on: September 19, 2012, 02:08:41 PM »

sounds like you need to know a lot more about the physics of your battery plant.

you can get this usage/predictive software for big commercial UPS units like Powermate and Liebert.  you either have to load the battery characteristics for the power stacks you are using, or the software has to have a few hours to dynamically determine rate of use and length of backup using temp sensors and tables, etc.  these are purpose-built for the dynamics of each manufacturer's systems.

to write it yourself, you must dynamically monitor the battery stack voltage and current use by ADCs, one across a shunt resistor, monitor ambient and battery stack temperature, figure in the dynamic power use from the load (in this case T to R ratio, etc) and finger out the math.  you will have to have a voltage/current table for your battery stack to work against, with the "orange line" and "red line" conditions for warnings to avoid low voltage or overdrain damage.

if you have the device table each instance and rewrite flash tables with actual results, like the engine control computer does in a car to have a dynamic record of how you drive, it gets better with time.

but it's a nice exercise in programming.  you've now got a roadmap.  decide where you want to go, and then reduce it to math and data collections.  the actual electronics is basically sling black boxes together, that is the easy piece of the project.  having it do something other than blink lights and put up nonsense numbers is the part that takes work.
« Last Edit: September 19, 2012, 02:24:28 PM by KD0REQ » Logged
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