Leisure battery charging

[Tarquers]

Did some research to understand charging of leisure batteries after hearing about 80% capacity for smart alternators and put it to the test on a long run recently. Nothing smart about the alternator by the way, just the electronics that control its charging state.

The battery system works in such a way that the alternator only charges batteries under certain conditions to reduce emissions and also keeps capacity in the battery free for regenerative braking to work.

So scenario 1, accelerating. To reduce load on the engine the alternator does not engage. Scenario 2, coasting. The alternator engages to provide engine braking.

So in normal driving, the batteries charge together with the leisure batteries and are charged at a time when the van decides it’s appropriate to charge but only to 80%. Leisure batteries cannot charge more than the 80% either through driving.

When charged on EHU, battery voltage is higher than the no-charge state of the alternator so leisure batteries will discharge (only when engine on and relay engaged) to the 80% level due to the design (no cutout on leisure batteries when fully charged).

So how to test this? Simply drove along and watched the voltage on screen. Steady 12.7v. Then engaged forced charging. Steady 15v or so. Allows batteries to charge above 80% from both EHU and driving, then observed voltage, 12.7v and a negative amp flow.

Conclusion I came to is that to maximise leisure batteries for camping must keep max charge engaged or accept a lower length of time that the batteries will support a charge. If you know the site has an EHU, then it doesn’t matter, but otherwise for wild camping or day can use, you get up to 20% less performance with an (un)smart alternator.

 

[Wesel]

The solution for camping is the installation of solar panels.
They also charge up to 100%. (When it's sunny of course)

 

[yossarian]

When charged on EHU, battery voltage is higher than the no-charge state of the alternator so leisure batteries will discharge (only when engine on and relay engaged) to the 80% level due to the design (no cutout on leisure batteries when fully charged).

I'm not sure I follow this bit? It's there a typo here?

 

[flying banana]

If you have heated seats,leaving 1 switched on whilst driving keeps the alternator engaged all the time giving more battery power when you arrive

 

[Ch1pbutty]

Fit some solar panels, then you never need to worry.

 

[dspuk]

I guess you can also press the max charge button while driving so alleviating worry if you do not have Solar or EHU at your next stop. If you have one or other then no need to worry.

 

[Wesel]

I guess you can also press the max charge button while driving so alleviating worry if you do not have Solar or EHU at your next stop. If you have one or other then no need to worry.

No such button on the T6 unfortunately

 

[BenPcaliman]

Thread 'Victron Orion Dc Dc charger upgrade' https://vwcaliforniaclub.com/threads/victron-orion-dc-dc-charger-upgrade.43663/

Solar and new dc/dc charger works well for me

 

[Blue Yonder]

Alternator only charges to 80% to leave room for charge produced by engine braking. Lead acid batteries need to be periodically taken up to 100% charge state to keep them in good shape. Hence why VW ask you to plug in your hook up every month.

 

[WelshGas]

No such button on the T6 unfortunately

Headlights on, Heated seats on low or AirCon on will do the same , switching alternator to Max Charge. If you plug in a voltmeter into a Leisure powered 12v socket you’ll see the difference.

 

[Blue Yonder]

Headlights on, Heated seats on low or AirCon on will do the same , switching alternator to Max Charge. If you plug in a voltmeter into a Leisure powered 12v socket you’ll see the difference.

Headlights on, Heated seats on low or AirCon on will do the same , switching alternator to Max Charge. If you plug in a voltmeter into a Leisure powered 12v socket you’ll see the difference.

You learn something new every day.
Useful to know.

 

[Steve1]

Headlights on, Heated seats on low or AirCon on will do the same , switching alternator to Max Charge. If you plug in a voltmeter into a Leisure powered 12v socket you’ll see the difference.

Yep, with ours even setting seat heater to lowest setting put's the alternator fully on, and you can't even really feel the heat from that !

 

[andyinluton]

Hence why VW ask you to plug in your hook up every month.

In the T6.1 manual VW do not tell you to hook up every month.

They advise you to hook up if the van hasn’t been driven for a month.

 

[Blue Yonder]

In the T6.1 manual VW do not tell you to hook up every month.

They advise you to hook up if the van hasn’t been driven for a month.

I assume then the van must either automatically allow the alternator to fully charge to 100% periodically or you are advised to switch to "max charge" periodically. If neither true then my advice would to hook it up every month.

 

[Steve1]

I assume then the van must either automatically allow the alternator to fully charge to 100% periodically or you are advised to switch to "max charge" periodically. If neither true then my advice would to hook it up every month.

I think the usual charging profile that the "smart alternator" produces is generally fine to prevent damage to batteries, if the van is used frequently enough and distances driven are far enough for it to charge the batteries properly. Very low charge can destroy lead acid batteries which is why they recommend you plug the hookup in if you don't use it often enough (or far enough). The "smart alternator" charges to a suitable level and then adds pulses of much higher voltage everytime you go down hill and release the throttle pedal (pseudo regenerative braking). It is true that in certain conditions the battery will not be fully, fully charged when you stop (which may be inconvenient if you need full leisure batteries, but it will be charged enough not to be damaged. During normal use they do get close to full and peak up and down depending on use etc. If this wasn't the case then you wouldn't expect the starter battery on all "smart alternator" vehicles to last very long either, but I have not heard of any problems with them.

 

[chockswahay]

Adding to this thread. I had the car on EHU at home this week then after washing the wheels took a short drive around the block to dry off the discs (not relevant really). The No load SOC was about 12.8v. Anyway I noticed that as soon as I started the engine there was a discharge showing on the main panel of about 10 amps! (12.2v/-10a). Is is possible that the engine battery will ‘steal’ power from the leisure batteries if they are higher charged? I pressed the max charge button and the situation reversed (14.8v/+10a).

After the drive I checked again and these photos show the difference…… the exact numbers have changed but you can see the difference. Any thoughts anyone?

 

[chockswahay]

Further to this I noticed what @Tarquers said about the alternator only charging when decelerating…… I wonder if this accounts for quicker discharging leisure batteries when doing long journeys (say on motorway or dual carriageways with little braking etc) with the fridge on for example?

 

[Steve1]

Adding to this thread. I had the car on EHU at home this week then after washing the wheels took a short drive around the block to dry off the discs (not relevant really). The No load SOC was about 12.8v. Anyway I noticed that as soon as I started the engine there was a discharge showing on the main panel of about 10 amps! (12.2v/-10a). Is is possible that the engine battery will ‘steal’ power from the leisure batteries if they are higher charged? I pressed the max charge button and the situation reversed (14.8v/+10a).

After the drive I checked again and these photos show the difference…… the exact numbers have changed but you can see the difference. Any thoughts anyone?

View attachment 107542View attachment 107543

Yes exactly what you said. So when you start the van, and the engine is running the relay will join the leisure battery to the engine battery. If the engine battery is lower because you have charged the leisure up and the engine one is at the standard 80-90% that the smart alternator aims for AND if the alternator is in the off part of its smart cycle because it thinks the engine battery is charged enough then current will flow from the leisure to the engine battery until they match.
If at any time the alternator switches back on again to any level above 12.8V then charge will stop flowing out of the leisure. So when enabling the max charge (or seat heater in older vans) a voltage much higher than 12.8V is applied maybe around 14.4V and both batteries charge to full

 

[Steve1]

Yes exactly what you said. So when you start the van, and the engine is running the relay will join the leisure battery to the engine battery. If the engine battery is lower because you have charged the leisure up and the engine one is at the standard 80-90% that the smart alternator aims for AND if the alternator is in the off part of its smart cycle because it thinks the engine battery is charged enough then current will flow from the leisure to the engine battery until they match.
If at any time the alternator switches back on again to any level above 12.8V then charge will stop flowing out of the leisure. So when enabling the max charge (or seat heater in older vans) a voltage much higher than 12.8V is applied maybe around 14.4V and both batteries charge to full

And further to that @chockswahay I usually leave everything to sort itself out if I am doing non camping related journeys or have hookup at the destination, the charge it puts in is plenty for that. But if I am going to be off of hookup and trying to get the most out of leisure batteries I always turn on the seat heater on low (max charge button for you) at least an hour before arriving at the destination to make sure the batteries are really topped off.