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Author Topic: Digital Voltage meter & battery  (Read 1448 times)

RAAArtyGunner

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Digital Voltage meter & battery
« on: October 14, 2016, 06:04:57 AM »

What are the pros and cons if any, to leaving a digital voltage meter connected to a battery. Either in use or stored.

The volt meter would display the current voltage at that time and would no doubt use some current until the battery becomes flat.

However by that time the battery would (should) be back on charge.

Instead of tagging the battery with the date it was recharged, looking at the meter would indicate if it ready for use, or am I missing something??

These digital meters are relatively inexpensive so would not break the bank.

Am not thinking of Lipo's etc, only Gel cells, Ni cads and NiMh's.
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inertia

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Re: Digital Voltage meter & battery
« Reply #1 on: October 14, 2016, 09:09:20 AM »

In storage, batteries will self-discharge over time because of their own internal resistance but if you connect a load across them - even a low current one like a DVM - then they will discharge a lot faster.
NiCAD and NiMH batteries have a high voltage when first charged - up to 1.5v when new. This drops quickly down to their nominal voltage (1.2v) and remains there until they are over 90% discharged, then the voltage drops very rapidly. For NiMH cells the absolute minimum voltage should be 1.0v/cell. Unless you check them very regularly you run the risk of them going below this and into deep discharge, which can damage cells fatally. Unfortunately connecting a DVM across a cell will give no indication of how far along the V/T curve the discharge has gone i.e. how much charge remains. I wouldn't do it, but that's only my opinion.
When in use, however, you will be taking a significant amount of power from them and so the addition of a DVM will make very little difference to the rate of discharge e.g. the voltmeter/battery state indicator on the front of a transmitter.
DM
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plastic

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Re: Digital Voltage meter & battery
« Reply #2 on: October 14, 2016, 10:31:23 AM »

Out of curiosity, would the DVM be powered from the mains or batteries?

If you're not there looking at it 24/7, why would you want it connected?

I can understand hooking up a data logger to log the performance of each battery so you can trend the data - but why?
Is your life incomplete without the data?

Models anen't super-critical devices - especially boats - when the battery runs down they just stop & bob about until the wind blows them to the side.
Just make sure you have spares & stick another in to continue playing.
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RAAArtyGunner

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Re: Digital Voltage meter & battery
« Reply #3 on: October 14, 2016, 11:27:26 AM »

Many thanks. :-))

Definitely a bad idea, so won't be that lazy.

Have now also learnt the cause of some of my battery woes. Namely, infrequent checking. {:-{

Will now mend my ways and get better organised. O0
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inertia

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Re: Digital Voltage meter & battery
« Reply #4 on: October 14, 2016, 11:30:14 AM »

I suspect that RAAAG has seen something like this http://www.componentshop.co.uk/general-purpose-voltage-meter-white-0-28-7mm-display.html
which isn't exactly what you and I would interpret as a digital volt meter (a big thing with multiple ranges and test probes). This is more of a voltage monitor and consumes 50mA i.e. enough to flatten a fully-charged 2600mAh Rx pack in just over four days.
The only way of determining how much charge is left in a battery is to discharge it across a load and measure the time it takes and the current it draws - there's no way of taking the lid off and looking inside or shaking it to see how much it rattles!
Dave M
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RAAArtyGunner

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Re: Digital Voltage meter & battery
« Reply #5 on: October 14, 2016, 11:37:28 AM »

I suspect that RAAAG has seen something like this http://www.componentshop.co.uk/general-purpose-voltage-meter-white-0-28-7mm-display.html
which isn't exactly what you and I would interpret as a digital volt meter (a big thing with multiple ranges and test probes). This is more of a voltage monitor and consumes 50mA i.e. enough to flatten a fully-charged 2600mAh Rx pack in just over four days.
The only way of determining how much charge is left in a battery is to discharge it across a load and measure the time it takes and the current it draws - there's no way of taking the lid off and looking inside or shaking it to see how much it rattles!
Dave M

They are what I was talking about.

Have one of the others, Digital Multi Meter, actually it's my son's but I get to use it.
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NFMike

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Re: Digital Voltage meter & battery
« Reply #6 on: October 14, 2016, 12:11:13 PM »

Most DMM turn off automatically after a time anyway, to save their own battery, so with one of those you'd probably need to wake it up anyway.

All rechargeable batteries need 'refreshing' occasionally. I just got a power bank for my wife's phone that has a lithium battery and even that says to recharge it every four months even if not used, to avoid permanent damage. For lead-acid batteries I do them every month as a rule.

Kipper

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Re: Digital Voltage meter & battery
« Reply #7 on: October 20, 2016, 04:57:57 PM »

when the battery runs down they just stop & bob about until the wind blows them to the side.
Just make sure you have spares & stick another in to continue playing.

 {-) not on our lake you don't, it's in a nature park & only at a few certain points can the waters edge be accessed, even then some of these points have overhanging green stuff that snares the boat before it's within reach.  O0

Not everyone sails on a man made pond with access all round like a paddling pool, some of us are 'deep water' sailors.  :-))
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