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Forum Index : Electronics : independent battery volt reading.

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irishron40
Senior Member

Joined: 22/09/2014
Location: Ireland
Posts: 251
Posted: 11:53am 06 Dec 2014
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just wondering how this can be achieved.

i have a charging system connected to battery thru a relay.

voltage from charging system could reach up to 30vdc.

if you look at relay , battery is connected to pin 87a and my charging supply to pin 30.

now i just wonder. when voltage drops from battery the relay will

i have a voltmeter connected to my battery which will show me current state of battery , and i would always like to be able to see that,

when battery is full my circuit will switch to pin 87.
at that point volt meter will show correct battery voltage.

but as soon my circuit connects pin 30 to 87 a my voltmeter will read the voltage of my charging supply.
I dont want that.

is there a way arround this without using a switch?4

regards.

ron

Edited by irishron40 2014-12-07
 
yahoo2

Guru

Joined: 05/04/2011
Location: Australia
Posts: 1166
Posted: 04:05pm 06 Dec 2014
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Hi Ron,
I would like to help but the symptoms you are describing do not match your description of your wiring. It could be that the volt meter is not connected how you think, the volt meter should always read close to the battery terminal voltage. Or there is a wiring/connector dry joint or fault somewhere. Have a good look at where the volt meter is connected and explore the voltages around this area with a multimeter with the relay in both positions paying attention to where both the +ve and _ve are connected.

If yo get no joy with that, at this point probably the best thing you can do is grab a chair and a cuppa and spend 30 minutes with a multimeter probing your wiring while the batteries are charging.

Start at the battery terminals and note the voltage and leaving the negative probe connected to the -ve terminal work your way with the +ve probe along your +ve wiring.

you are looking for a rise in voltage between two points. The same thing can be done working along the -ve wiring.

Once you get out of arms reach form the batteries I normally switch to a different technique and use both probes along the one wire and look for a reading that is not close to zero.

Remember this only works for finding high resistance when the wiring is under load, I normally hook up a 100+ watt light to the battery terminals to make sure that the power keeps flowing.

Hope this helps a little, its about the best i can do with limited info.

yahooEdited by yahoo2 2014-12-08
I'm confused, no wait... maybe I'm not...
 
irishron40
Senior Member

Joined: 22/09/2014
Location: Ireland
Posts: 251
Posted: 09:55pm 06 Dec 2014
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thank you, i gaveto much info i think. if i connect voltmeter strait onto battery it will read just battery power.

but am i correct in thinking, that the moment i connect my wind turbine which produces higher voltage then battery level, that volt meter reads that vallue?
 
yahoo2

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Joined: 05/04/2011
Location: Australia
Posts: 1166
Posted: 10:33pm 06 Dec 2014
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  irishron40 said  
but am i correct in thinking, that the moment i connect my wind turbine which produces higher voltage then battery level, that volt meter reads that vallue?


It is more of a balance between the two, in a brisk wind the turbine could be putting out 25-40+ volts, the battery bank is using the resistance of the chemical reaction in charging to hold the voltage down.

so a half charged battery that is resting at 12.3 volts will be reading 13.8 to 14 volts under a good charge current.

a full battery rests at 12.5-12.7 volts and will be at 14.4 - 14.8 volts while charging.

exactly the opposite happens when you apply a load, the chemical reaction cant keep up with the current draw and the voltage slumps.
So 12.3 volts resting will be 11.9 volts with the electric kettle on the boil.

that is why it is so handy to know where the current is going when you are looking at the battery voltage.

what you should not be seeing, is a voltage reading from your meter that is above the voltage that your relay is set to switch to the dump load. Something is not wired correctly if that is the case.
I'm confused, no wait... maybe I'm not...
 
irishron40
Senior Member

Joined: 22/09/2014
Location: Ireland
Posts: 251
Posted: 01:15am 07 Dec 2014
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  Quote  what you should not be seeing, is a voltage reading from your meter that is above the voltage that your relay is set to switch to the dump load.


thats answers my question.

at 15 volt it swiches to dumpload. so my battery voltmeter will never show more then 15v max.

thank you (-: (still a lot to learn)
 
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