# Vehicle Charging Leisure Batteries



## 100127 (Jul 20, 2006)

Can anyone tell me at what rate the engine/alternator charges the leisure batteries?
I know it is a high rate when charging the vehicle battery, so it must be a much lower rate for the leisure batteries. Reason I am asking is, stopped at a Britstop for one night, no ehu, and used the TV for at least 5 hours, and lights etc. Next morning only a 3 hour drive to Millers Field, again no ehu. Used TV for at least 4 hours and lights and used the inverter for our microwave 800watts for about 6 minutes. So far, no problems. Next morning, put on tv for news and after 10 minutes it switched itself off as battery levels were low. Weather for those two days were very overcast so 100 watt solar panel on roof was not working much. I have twin 110 amp batteries. I would have thought I could have lasted on battery power for longer, or am I being over expectant?
Cheers.


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## rayc (Jun 3, 2008)

My CBE system contains a Electronic Battery Seperator.
It is controlled by the + Key engine starting, switches on the battery
parallel when the alternator voltage is under 13,3V and switches it off when the engine starting key is off or the voltage is under 12V.

Therefore it appears the habitation batteries will not receive the 14+ volts that the cab battery does but only 13.3v or below.


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## gengis (Dec 6, 2013)

Everyone assumes an alternator charges at a high rate, but the rate it charges at is entirely dependant on the state of charge of your batteries - just like a battery charger or a solar panel.


An initial high kick of initial amps will drop in minutes to the batteries required level for state of charge and from there drop slowly as the battery charges and you arrive at a very low current of 0.25a signifying your batteries are fully charged.

The current draw of a battery charging is far more accurate than reading the voltage.

In a twin battery bank or triple bank you can also measure the current draw of individual batteries on charge and compare them. Finding one drawing much less current signifies a battery able to store less power and on its way out. That battery will drag the other one or two down when in use and will be exaggerated in cold weather and when drawing high currents.

( An alternator only has a crude regulator which is why people pay £300 for the 50a battery to battery charger that can make use of the current an alternator can potentially produce.)


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## listerdiesel (Aug 3, 2012)

gengis said:


> ( An alternator only has a crude regulator which is why people pay £300 for the 50a battery to battery charger that can make use of the current an alternator can potentially produce.)


Alternators have quite sphisticated regulators, and they have to contend with all of the electrical switching on and off surges, high under-bonnet temperatures and extremes of climate, but they are still probably the most reliable part on the car.

Regarding the original question, it's difficult to make a judgement without knowing what connections there are between the LB and the vehicle battery.

If the batteries were fully connected in parallel, the alternator would run at its full output until it sensed that the batteries were coming up on charge to the point that it could ease off a bit, but it doesn't 'know' what is connected to its terminals, it just runs according to what it sees happening at its terminals.

Looking at the original post, it sounds to me as though the LB isn't getting much charge, if any, from the vehicle alternator.

Peter


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## 100127 (Jul 20, 2006)

listerdiesel said:


> Looking at the original post, it sounds to me as though the LB isn't getting much charge, if any, from the vehicle alternator.
> 
> Peter


Thanks Peter, just what I thought, just wondered where the split relay charger was in my MH. :?: :?:


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## gengis (Dec 6, 2013)

listerdiesel said:


> gengis said:
> 
> 
> > ( An alternator only has a crude regulator which is why people pay £300 for the 50a battery to battery charger that can make use of the current an alternator can potentially produce.)
> ...


You cant tell people that !

Are you seriously saying a bog standard 120a alternator "will put out its full output until it sensed the batteries were coming up to charge"

You are wrong just as in other posts you suggest cold temperature has little effect on batteries.

Get a grip !

Just for the record - an 800w microwave used for 6 minutes will use 51 AH from your battery bank of 2 x 110AH.


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## listerdiesel (Aug 3, 2012)

gengis said:


> You cant tell people that !
> 
> Are you seriously saying a bog standard 120a alternator "will put out its full output until it sensed the batteries were coming up to charge"
> 
> ...


An 800W microwave on a 95% efficient inverter will use 840W approximately. At 12.5V nominal that will be 67.20amps.

67.20A for 6 minutes or 1/10 of 1 hour looks like 6.7AH to me, I can't speak for your own figures, but they are pretty obviously incorrect.

Peter


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## listerdiesel (Aug 3, 2012)

Sysinfo said:


> listerdiesel said:
> 
> 
> > Looking at the original post, it sounds to me as though the LB isn't getting much charge, if any, from the vehicle alternator.
> ...


Or indeed, have you actually got one?

Peter


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## 100127 (Jul 20, 2006)

Hmm food for thought, must get it checked out.


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## adonisito (Nov 6, 2009)

We can last much longer than that on our 2 110amp batteries, including fan assisted gas heating. All vans are different but to me that would indicate a duff battery or that a microwave on an inverter is not a good idea ! :lol: Mind you I have changed all our lighting to LED as we spend a lot of time off hook up in the Winter.

As regards the leisure batteries charging off the engine alternator, I will check if ours do tomorrow.


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## safariboy (May 1, 2005)

A big factor will be the resistance between the batteries and the alternator. The alternator output will change from full to practically nothing with a change in voltage of the alternator terminals of about 1.5V or even a bit less. But the current through the wires to the battery will itself produce a voltage that will tell the alternator to reduce the charge. I suspect that with the standard set up 10A is probably the maximum current.
The solution is a more sophisticated charge controller with a separate sensor wire to the battery for the voltage sensing. This wire has no current flowing and so the voltage at each end is the same and the full current is available. 
If you want to rely on the van engine charging the leisure battery this sort of thing might be a good investment. I am sure that someone else will come up with brand names.


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## WildThingsKev (Dec 29, 2009)

rayc said:


> My CBE system contains a Electronic Battery Seperator.
> It is controlled by the + Key engine starting, switches on the battery
> parallel when the alternator voltage is under 13,3V and switches it off when the engine starting key is off or the voltage is under 12V.
> 
> Therefore it appears the habitation batteries will not receive the 14+ volts that the cab battery does but only 13.3v or below.


I think you've misinterpreted a poor translation in the CBE manual. What "when the alternator voltage is under 13,3V" really means is that when the (increasing) Vehicle Battery voltage reaches about 13.25V (I tested it to check) the EBS/SCR will start to supply the Leisure Batteries.

Also bear in mind that if you have the fridge setting turned up whilst driving then the 15A it takes will knock the LB charging voltage down to about 13.5V. The fridge can run for a high percentage of the time, so if you turn the fridge to a low setting (and it clicks off) you will see the LB volts jump up to >14V, thus getting a more rapid charge.

This is certainly true for Rapido's, I think most modern vans will be the same.

Safariboys final comment is pertaining to "Battery to Battery Chargers". I've just fitted a German "Votronic" one which I'm very pleased with but the more usual ones are by Sterling and CTEK.

Kev


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## 100127 (Jul 20, 2006)

Further to my OP, I have checked with a multimeter the LB's with engine off, and then with engine running. Result they are being charged by the engine.   Kev I had not taken the fridge into account , so that's food for thought. Can anyone tell me what the expected output from a 100 watt solar panel on a sunny day. Could I expect 4 amps??


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## listerdiesel (Aug 3, 2012)

You'd get comfortably more than 4amps at the peak sunshine hours when the sun is overhead.

Peter


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## safariboy (May 1, 2005)

It will depend on the state of the battery. The panel is probably about 18V so 4A is 72W. Then your regulator is probably effectively simply a resistor whore value is controlled by the output voltage so you lose the 4V or so to heat.
Your 4A seems reasonable and is about my maximum in UK. I have got about 9A but that was with the sun overhead in Morocco and the battery did need a charge.
There are better regulators (MPPT) that are able to deliver most of the power to the battery but these are less common. If you have a battery powered compression fridge for example it could be a good idea.


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## listerdiesel (Aug 3, 2012)

I don't think anyone is fitting anything too simple as far a solar regulators go, at worst it is probably a PWM type, cheaper than MPPT but quite effective for a low-cost unit.

We've never really checked ours for output amps as we rarely get our single battery down that low, and our system is split so there are 2 X 80W panels and MPPT controller for our domjestic stuff and the other two panels, controller and regulator are for the trailer electrics, winch etc.

On the few occasions when we have had a look, we've rarely seen much more than 4-5A, as by mid-morning it has been charging since just after sun-up and it all goes towards recharging the battery, however small.

8AH** at night for TV, satellite receiver and a couple of lights, soon gets put back into the battery.

Peter

** Based on 3A drain for TV and receiver and 1A for small lamps, all for a couple of hours or so. Nothing else taking anything, the fridge is gas, water heater is gas etc.


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