Battery Voltage readings

[Lorenzo Senior Member Find all posts View Profile Close Lorenzo]

Hi All,

after all the woes I had last week, I think I found out what was happening. The first few months of owning this dual battery system, I treated my aux like a bit of a refugee camp prisoner. Never fed it enough and demanded too much of it!

On wednesday night last week I stuck it on the charger overnight and the voltage was back up to about 12.73 I then plugged the fridge in and drove 8 hours. Over the next 3 days the car drove 10 mins a day but with absolutley no load on aux. I then drove back home at another 8 hours with fridge plugged in. Fridge has now been on since sunday night and I've been driving 25 mins to work and 25 mins back. with the fridge set at 0 degrees ever since I left on sunday lunchtime. Just went and tested it now and the reading is 12.4. and it has been running the fridge for the last 5 days straight.

I think it just needed a good charge and be reminded of what full status feels like. Now, with my hour of driving a day it's enough to charge the battery enough to keep running the fridge and maintain a similar SOC every morning. Very happy with it now!

All it needed was a good charge. When my experiment ends, I'll turn the fridge back off again as I don't need it on 24/7, and make sure that once a fornight/month or before a camping trip I give it a fair old rev up with the charger.

Thanks all for your input!

I'm still getting a .1v drop from main to aux but think it may be related to my wiring. I'll test everything out this weekend and update you all.

Cheers,
Lorenzo

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

Leigh,
finally have dual battery system up and running in my 120 series. Just wanted to thank you as I found answers to all my questions, and solutions to all my hurdles by reading your replys to other forum members. Used one of your boosters purchased off ebay. Couldn't be happier, seconds to fit and worked just like you said.

Thanks again


PARSO

Hi Parso,

That's great, good to read that the unit is working well for you,
happy motoring

Cheers
LeighW

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

The web has plenty of info and the table I have copied is a general guide. If you google your battery it is likely there is a specific chart for it.

State of Charge Sealed or Flooded Lead Acid Gel battery AGM battery
100% 12.70+ 12.85+ 12.80+
75% 12.4 12.65 12.6
50% 12.2 12.35 12.3
25% 12 12 12
0% 11.8 11.8 11.8

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Hi mjrandom, the figures you have posted are for OPEN CIRCUIT voltage readings and are of little use unless the battery has been sitting in a No-Load/No-Charge state for at least 24 hours.

You can get a much more accurate indication of the state of charge of a battery using a loaded voltage table with a small load connected to the battery ( like a compressor fridge ).

This table is the same for all types of automotive lead acid batteries, flooded wet cells, Gels and both Standby and Automotive type AGMs.

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

That's the chart I have in the glovebox, I just googled and posted figures without looking too hard. Thanks for the updated info.

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Hi again mjrandom, and not a problem.

Unfortunately when googling, most of the time, the OPEN CIRCUIT chart comes up but it rarely has the relevant info with it to show how to use it properly.

The link below is to info provided by Trojan batteries and gives a good explanation of how to properly use an OPEN CIRCUIT table.

http://www.trojanbattery.com/Battery...e/Testing.aspx