Battery reading false results (1 Viewer)

ojbristow

Free Member
Nov 26, 2022
2
0
Funster No
92,622
MH
Transit14 Self Bulid
Hey all!

Currently converting a van and on the electric side of things now, all hooked up and working. Have a pair of new 95ah batteries (AGM) linked together and hooked up to solar panels, split charge relay, inverter and other minor elctrical devices.

The panels that have volt readings built in (Solar controller, invertor and diesel heater) show the batteries seem to drain very quickly from 12.9 to 12.4v. This is when using x6 led lights or just the diesel heater, super low loads which shouldn't even make a dent in the charge.

I have now unplugged everything fully charged with mains charger both batteries individually and verified they are now fully charged. Hooked electrics back up. Ran minor applicances for literally about 15 minutes. Now the volt meter readings on the invertor and solar controller are reading low voltage again at around 12.5v. Unplugged everthing and checked the batteries are actually running at 13.0v and 12.9v so I don't think the batteries are at fault.

Is there anything that could be causing the false readings on the devices when they are linked together? Hopefully it's just me being daft and missed something silly but I'm puzzled and figured to put the question out there.

Hope this makes sense, thanks!
Owen
 
Aug 4, 2019
1,923
8,510
North East Riviera
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62,993
MH
Low profile
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Enough to Survive
Details of your equipment and maybe even pictures of your wiring configuration may help people to advise.

Incorrect sized wiring could exaggerate the lower readings due to voltage drop along the cable run to the various device displays.

On start up your diesel heater isn’t a ’super low load’ it’s actually quite high while the glow plug is energised, but still shouldn’t cause the issue your describing.

What size cable did you use and how long are the cable runs for your devices.

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Last edited:
Upvote 0
May 29, 2013
2,628
19,486
Tyneside
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26,231
MH
Chausson best of Flash 10
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Several years now
Hey all!

Currently converting a van and on the electric side of things now, all hooked up and working. Have a pair of new 95ah batteries (AGM) linked together and hooked up to solar panels, split charge relay, inverter and other minor elctrical devices.

The panels that have volt readings built in (Solar controller, invertor and diesel heater) show the batteries seem to drain very quickly from 12.9 to 12.4v. This is when using x6 led lights or just the diesel heater, super low loads which shouldn't even make a dent in the charge.

I have now unplugged everything fully charged with mains charger both batteries individually and verified they are now fully charged. Hooked electrics back up. Ran minor applicances for literally about 15 minutes. Now the volt meter readings on the invertor and solar controller are reading low voltage again at around 12.5v. Unplugged everthing and checked the batteries are actually running at 13.0v and 12.9v so I don't think the batteries are at fault.

Is there anything that could be causing the false readings on the devices when they are linked together? Hopefully it's just me being daft and missed something silly but I'm puzzled and figured to put the question out there.

Hope this makes sense, thanks!
Owen

Define minor appliances. When we put the diesel heater on it takes a surprising amount of current, even after the initial switch on.

If you want exact science, buy some high wattage resistors of 48ohm, 24ohm and 12ohm. Put them individually across the batteries, with no other load at all ! The 12ohm one will give a load of 1A, 24ohm will give a load of 0.5A and 48ohm will give a load of 0.25A, then watch what the voltage of the batteries do, measure directly on the battery terminals with a multimeter and compare to your other displays.
 
Upvote 0
Apr 27, 2016
6,931
8,096
Manchester
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42,762
MH
A class Hymer
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Since the 80s
Do you have a multimeter to take readings at various points in the circuit? First thing to find out is if the battery voltage is really going down, or is there a voltage drop along the wires, or maybe the displays don't show an accurate voltage reading.

You need to take voltage readings at the actual battery terminals, positive and negative. First with the battery 'resting' (no charging, no load) then with a load taking a typical current. While you are there you could double-check the voltage on the wires next to the terminals, to be sure there's no voltage drop from a bad terminal contact for example.

Then check at the solar controller terminals and see if the multimeter reading agrees with the solar display.

Then, with a load connected, compare the voltage at the battery with the voltage at the terminals near the load. That will tell you whether the voltage drop is due to the battery or the wires.
 
Upvote 0
Jan 28, 2008
10,137
18,421
Dovercourt, Harwich, UK
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1,353
MH
Renalt burstner
Exp
7 years campers before that
deisel heater of the chinese variety often come with very under size power cables if youve matched the cable to run it to whats there it will be undersized
 
Upvote 0
Feb 14, 2022
177
417
Sheffield, UK
Funster No
86,876
MH
Nissan NV400 self bu
Surely if any load is applied to the batteries the voltage will reduce?
Mine does with 2 brand new 130ah batteries, lights on (led) and it drops a smidge but comes straight back up when turned off.
Also the diesel heater can draw 10 amps on startup, dropping to 1 amp when up to speed.
 
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