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[on:]

Hi Now have a voltage sensor using voltage divider , I'm measuring a solar battery bank .
This bank has a lot of amps 1000, and a lot of high amps devices inverters etc
When the inverter push by the battery arduino some times get strange USB results on the pc side  ...
So going direct I want to measure voltage without having common grounds..
At first I was thinking in 2 arduinos that communicate wireless
One measuring voltage other connected to pc ..
Then one arduino wireless connected but...
Must be a way to this cheaper and easy ..

Please give me advices ..
Regards

[Reply #1 on:]

i had the idea to do it with a mechanical relay that connects both ends of a capacitor first to the battery and then to the arduino... but i dont know if the relay likes it...

the other idea is: 1 ATtiny13 for each battery (powered by that battery) and communication with the "central" via opto-couplers...   

[Reply #2 on:]

For now I dont want to measure. Individual cells, just all bank total  range from 23v to 30v...

[Reply #3 on:]

ok
u could still use that relay idea with a voltage divider and a 35V capacitor:

http://www.falstad.com/circuit/#%24+1+5.0E-6+81.92041607667615+50+5.0+43%0A178+208+112+288+112+0+2+0.2+0.02563182296591928+0.05+1000000.0+0.02+178.0%0Ag+208+160+208+176+0%0Aw+208+144+176+144+0%0AR+176+144+80+144+0+2+100.0+2.5+2.5+0.0+0.5%0Ac+128+64+128+112+0+9.999999999999999E-5+29.999998525073813%0Aw+128+112+208+112+0%0Aw+128+64+208+64+0%0Av+288+128+352+128+0+0+40.0+30.0+0.0+0.0+0.5%0Ag+384+96+384+112+0%0Ar+288+48+384+48+0+33000.0%0Ar+384+48+384+96+0+1000.0%0Ap+480+48+480+96+0%0A167+480+48+576+48+0+4%0Ax+500+189+551+195+0+24+ADC%0Aw+384+48+432+48+0%0Aw+432+48+480+48+0%0Aw+384+96+432+96+0%0Aw+432+96+480+96+0%0AR+480+144+448+144+0+0+40.0+1.1+0.0+0.0+0.5%0Aw+288+96+384+96+0%0Ac+432+48+432+96+0+1.0E-7+0.01474927170325975%0Aw+288+80+352+80+0%0Aw+352+80+352+128+0%0Ad+208+160+176+160+1+0.805904783%0Aw+176+160+176+144+0%0Ao+11+8+0+34+1.25+9.765625E-5+0+-1%0A

[Reply #4 on:]

Thanks but I'm bit lost with your diagram I will try to understand this better on the conputer.
But how does a relay and a capacitor isolate grounds ?

Rhanks

[Reply #5 on:]

maybe my drawing is a little bit too weird...  

the isolation works as follows:
1. when the capacitor is connected to the battery pack, it is not connected to arduino ground (not even via a voltage divider... air is a good isolator...)...
2. when the capacitor is connected to the voltage divider, it is isolated from the battery (again by air)...
 

does the URL work for u?
it doesnt work for me...

PS: i took the idea from the LTC1043 datasheet...  

PPS: the relays might need external fly back diodes...

PPPS: i changed the picture a little bit... it might be easier to read now...

[Reply #6 on:]

Hi no the link dont work and now no picture on the post

[Reply #7 on:]

then u can use the File-Import method with this (it is animated): 

Code:

#$ 1 5.0E-6 81.92041607667615 50 5.0 43
178 208 112 288 112 0 2 0.2 0.02563182296591928 0.05 1000000.0 0.02 178.0
g 208 160 208 176 0
w 208 144 176 144 0
R 176 144 80 144 0 2 100.0 2.5 2.5 0.0 0.5
c 128 64 128 112 0 9.999999999999999E-5 29.999998525073813
w 128 112 208 112 0
w 128 64 208 64 0
v 288 128 352 128 0 0 40.0 30.0 0.0 0.0 0.5
g 384 96 384 112 0
r 288 48 384 48 0 33000.0
r 384 48 384 96 0 1000.0
p 480 48 480 96 0
167 480 48 576 48 0 4
x 500 189 551 195 0 24 ADC
w 384 48 432 48 0
w 432 48 480 48 0
w 384 96 432 96 0
w 432 96 480 96 0
R 480 144 448 144 0 0 40.0 1.1 0.0 0.0 0.5
w 288 96 384 96 0
c 432 48 432 96 0 1.0E-7 0.01474927170325975
w 288 80 352 80 0
w 352 80 352 128 0
d 208 160 176 160 1 0.805904783
w 176 160 176 144 0
o 11 8 0 34 1.25 9.765625E-5 0 -1

is the picture back?

[Reply #8 on:]

Have you considered to use analog optocouplers? Like this one:

http://www.conrad.ch/ce/de/product/140035/OPTOKOPPLER-HCNR201-000E