Charging batteries with engine idle

[No_heroes]

This may have been covered many times, but I did a little experiment today.

T6 199 engine. I let the battery readout go down to 50%. With the fridge on 6 and some items charging like a wireless speaker etc I ran the engine to see how long it would fully recharge the readout back to 100%

I let the engine idle for 20 mins and checked. It reported back at 100%

May not be that useful or accurate test and certainly not scientific but gives me confidence on offgrid power etc.

 

[TripleBee]

This may have been covered many times, but I did a little experiment today.

T6 199 engine. I let the battery readout go down to 50%. With the fridge on 6 and some items charging like a wireless speaker etc I ran the engine to see how long it would fully recharge the readout back to 100%

I let the engine idle for 20 mins and checked. It reported back at 100%

May not be that useful or accurate test and certainly not scientific but gives me confidence on offgrid power etc.

In 20 minutes the display will show 100%, but what ampere was there still going in your batteries? That is the main goal. The moment the batteries take no more amperes, then they are full.

 

[GSX1300R]

I have had our batteries go down to 20% then take a trip to our local Aldi (2 miles) it will show 100% for a very short time but run back down to 20% in no time.. The only way Ive found is to mains charge overnight or do a 200 mile run.

 

[No_heroes]

I still don’t have a good grasp of Volts, Amps and Watts. I don’t have it clear in my mind how power is stored, flows and is consumed. Ie battery, charge etc. As well as the creation from the alternator and it’s specification under different loads idle, driving etc.

How they relate and how time i.e. the ‘hours’ element plays into it.

Is there a link or spreadsheet as an idiots guide?

 

[GrannyJen]

Almost always when running the engine the battery indicator will show 100% .... then after a few minutes it will tick down to what it thinks the real level is! Best check after 30 minutes or so and see what the level is then.

 

[No_heroes]

After stopping the engine it has held at 100% dropped to 90% after an hour. Same load.

 

[GSX1300R]

After stopping the engine it has held at 100% dropped to 90% after an hour. Same load.

Check it again after a few more hours. But if it works for you then go for it....

 

[No_heroes]

Will check in a while!

 

[GrannyJen]

I only query it because when we go away, Alfie towing my Sisters caravan, we use my fridge as the freezer so I'm quite used to seeing the level drop below 40% and there ceases to be enough voltage to drive the fridge when it gets to 30% so the freezer is kaput and our dogs dinner is kaput with it

Problem solved now though, thanks to @Roger Donoghue fitting a solar panel for me.

 

[GSX1300R]

Will check in a while!

View attachment 48302

obviously with the fridge on it will run down quicker. I normally top ours up topped once a month on the mains...

 

[No_heroes]

I only query it because when we go away, Alfie towing my Sisters caravan, we use my fridge as the freezer so I'm quite used to seeing the level drop below 40% and there ceases to be enough voltage to drive the fridge when it gets to 30% so the freezer is kaput and our dogs dinner is kaput with it

Problem solved now though, thanks to @Roger Donoghue fitting a solar panel for me.

No one wants a hungry dog OR a hungry child OR a warm beer!

I’m tempted with solar- unsure why VW don’t integrate it factory. How is your install?

 

[TripleBee]

I still don’t have a good grasp of Volts, Amps and Watts. I don’t have it clear in my mind how power is stored, flows and is consumed. Ie battery, charge etc. As well as the creation from the alternator and it’s specification under different loads idle, driving etc.

How they relate and how time i.e. the ‘hours’ element plays into it.

Is there a link or spreadsheet as an idiots guide?

Look at it like a water tap.
The voltage is the diameter of the tube, the amperes is the flow. Watt is the total of water you get in a minute, hour, day...
So you can see between 12,2 and 13V, this is the diameter of the tube and doesn't change that much (less than 1V). You start your fridge, and it will consume about 4A = a certain waterflow.
If you have a battery of 110Ah (520A), this means you can draw 110A in 1 hour, and then your battery is flat.
You can get 520A out of it for just a very short period of time (just a few seconds, 1 or 2).
So, if your fridge is constantly drawing 4A (which is not the case, because when it is cool enough, the fridge stops drawing amperes), it takes over 27 hours for your battery to be flat. But the good thing is, you have 2 batteries, so you can multiply by 2, so over 50 hours of constant fridge (without the fridge stopping).

Try to get a look at the display of an SE, Ocean (electrohydraulic roof) when opening the roof. When the pump does it's 3 seconds pumping in the end, press the return button on the display, and you will see a current drawn from over 30A! But as this is just the time for opening the roof, the voltage will restore from 12,2 to 12,5 or more.

This is as easy as I can put it I think in a foreign language.

 

[GrannyJen]

No one wants a hungry dog OR a hungry child OR a warm beer!

I’m tempted with solar- unsure why VW don’t integrate it factory. How is your install?

I am hopelessly useless at anything DiY. If I tried to self-install I would have a pile of smouldering metal and rubber in no time so I popped down to Taunton and Roger installed for me. Took him about 40 minutes and my fridge has been running since with no interruption and batteries at 100%. Two very happy doggies

 

[WelshGas]

Will check in a while!

View attachment 48302

Rule of Thumb - Ignore the % Reading. It is a calculation based on current flow through an Earth Resistance under the Fridge.
Battery Voltage is more important and Current/Amps helpful and the Control Panel Display is reasonably accurate.
At 12.3 volts your battery is at about 70% capacity.