Alternator Charge Voltage with extra battery.

I think this is very interesting as raised in the recent 'Second Leisure Battery' thread which has been locked.



Here are the details which are very interesting and likely to be useful to many people, I have just measured mine and will post it first.



If you want to see just how good your vehicle manufacturer is at 'Electrics', measure the Alternator charge voltage at the habitation area batteries with the engine running and the Fridge on 12v.
If any body gets anywhere near the necessary fast full charging 14.4v that the Alternator puts out on a twin battery standard set-up, I will give them a free Habitation service.
 
We have never seen a UK vehicle with more than a poor 14.0v charge rate, usually nearer 13.8v, which many will know is the voltage mains chargers 'Trickle' at, so you can imagine the poor charging that will result.

Sometimes a single battery set-up will surprise us by showing almost 14.1v, but adding a second battery will place a higher load that usually causes further voltage drop so that that charge rate plunges further into the doldrums. An awful 13.7v is not unusual.

You can imagine what the 4 battery setup coming into us in two weeks is going to look like?
I am hoping the owner will allow us to document what we find, but from the thousands of chargers repaired in the past and the hundreds of Caravan and motorhomes we have worked on in a specialist Electrics role, I don't think it's going to support some of the existing views held on here. 

Please can we ask that forum readers really do check their charging voltages at the batteries on Alternator and post the results here? Note the batteries must have some discharge otherwise, obviously, the charging system will realise no charging needs to take place, 
This will provide real evidence of exactly of how the systems work as opposed to how the manufacturers tell us they work.

13.8 Volts for me.

I'm interested to hear at what rpm did you take your reading Will?

Hi Will,

It probably won't tell you too much about what the original vehicle manufacturer fitted, but if you're after a general impression of how good a split charge circuit has been fitted by the company that converted your van then a single figure might give you a rough idea - but there are some major factors that mean that what is "good" for one van might not be for another.

As an example, if it were a conversion on a VW T4 with both batteries in the engine bay then I would expect something major to be wrong with a figure of 13.8V. If it were my Celex on the other hand, where the leisure battery is about as far away from the alternator as you can get it, the figure would not be surprising or particularly worrying. Our Trooper is somewhere between the two extremes, with the leisure battery under the driver's seat.

The other major factor that will have a big effect on the figure is the recent charging history of the leisure battery. On both the Celex and the Trooper, I could reasonably assume that the leisure battery was close to being fully charged at all times (the Celex is always on EHU, and the Trooper has a 150W solar panel on the roof), though there could be some doubt about the Trooper in midwinter.

If you're unsure about the state of charge of the leisure battery then the voltage that you're measuring could vary in a big way - if, for example, it were partly discharged through standing unused for a week (especially in cold weather when self-discharge rates are higher) then it could initially be taking several (or lots of) amps from the alternator/engine battery. This is especially relevant on Auto-Sleeper conversions, because A/S have had a history of fitting relatively thin cables in their split charge circuits. In this situation it's not possible - without further measurement - to distinguish how much of the voltage drop is down to the load presented by the fridge, and how much by the charge being taken by the battery. The voltage drop depends on the sum of those two currents.

Another factor can be the state of the engine battery. Typically the cabling from the alternator to the engine battery will be much heavier duty than the split charge circuit. Immediately after engine start, the current taken by the engine battery can drag down the alternator voltage somewhat, and this can have an effect on the voltage "seen" by everything else in the van. If the van battery was in a low state of charge before engine start, this effect could last for a while.

Some other things which can influence the figure: the type of fridge. Most A/S conversions use absorption fridges, but not all do. If it's a compressor fridge the figure may be different in either a small or a large way (they tend to take less current, but more importantly the compressor is not on all of the time). The temperature is another factor, though not a large one, as far as I can see. In the UK it's probably only going to make maybe 0.2- 0.3V difference to battery terminal voltage in the normally expected temp range. On older vans, you may also need to account for the state of the alternator, as a significantly worn alternator can have a lower output voltage - though I suspect that most vans here are too new/well maintained for this to be a big effect. And as A/S_Don suggests, the voltage will depend to an extent on engine revs, as they typically can't generate their specified output current at engine idle.

[You also (of course) have to be sure that there are no other inputs and outputs that you don't know about - for example on the Trooper the solar panel would probably make the figure meaningless on a sunny day, but that's a bit too obvious to say, really!]

Edit: Reading that again, I'm aware that it was a long reply - probably too long!

The point I wanted to make is that - as an absolute, stand-alone figure - the voltage under those conditions doesn't mean too much, because it depends on too many things.

However, it can be very useful as a historical figure. If you know what it was on your van when the battery was new and everything was in a good state, keeping an eye on it can give you a very good hint if/when things start to go wrong.

As an indication of whether you could fit a second leisure battery, it would need more measurement and interpretation, IMO.

Thanks AutoSleepy_Don and –Mojo- I’m trying to keep my posts short as I’ve gathered that is what is required here.
 
 
I have always thought the engine charging on our Van is iffy. Peugeot 2.2 AS Warwick Duo, low miles, 2 habitation batteries I’m assuming fitted by AS but not sure as I’m not first owner. I was told “it’s a good van off hookup”
 
 
Solar charging seems to do a fantastic job in good weather, engine charging doesn’t.
 
 
My test………All the batteries fully charged by solar 22^nd Dec then stood idle.
 
 
Discharged leisure batteries (12.6v) with a couple of headlamp bulbs until down to 12.3v.
 
 
Connected my meter (a fairly decent Fluke with recording memory)
 
 
Started engine and drove off and did about 30 miles round trip. Temperature in van about 21C outside about 12C I guess.
 
 
Meter recorded (from engine starting) min 13.7V max 13.8v, on tick over 13.8v
 
 
2 Hours later 12.4v so re-connected solar.
 
 
The Caravan Chronicles website mentioned by AllaFEvans,
 
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has some very well written guides on this subject, there is a section regarding the use of a simple relay to simply fool the alternator into thinking 2 smaller batteries are just one big one. Seems a good plan to me …. Well maybe !
 
Can anyone tell me why the Second Battery thread was locked please, I though it really interesting and informative.

As far as I know Warwick Duos were only supplied with one leisure battery so I think previous owner has fitted the second one.

Peter Brown wrote:I monitored alternator charge voltage on my Mercedes for a couple of weeks about a year ago, the only constant was that it is variable!  I certainly did see 14.4/5 volts at times as I did many years ago measuring the voltage on my Ford based Duetto. You have to watch the voltage for at least 2 hours to get an idea of what's happening and at the end of the period, I was happy with the alternator charging process.

I didn't do any specific tests when I had the Peugeot but I do think that peaked at 13.7/8.

Peter, If the Alternator charging circuit is well designed and installed, the voltage at the habitation will be a constant while driving with the Fridge 'On', as the load should not change much, providing the Alternator is sized correctly for the battery bank.

It is nonsense to suggest you need to watch the voltage for 2 hours, the biggest peak will be just after start up, even one hour later the batteries will have warmed up and be on reduced charge. 
After two hours running a shallow charged battery bank will be back to full and not taking any charge so any measurement then will be irrelevant.


If you are seeing 14.5v at the habitation batteries then either there is some issue with your Alternator or it has Smart charging?

All good, conventional Alternators we have seen have been limited to 14.4v, with the exception of some Merc white vans with Smart Alternators running 14.7v peak but varying down to 13.7v when the batteries are charged?
Some Ford Transit white vans with Smart charging can also reach higher than 14.4v and drop to 13.8v but Ford normally disable that feature when it is ordered for a Motorhome conversion?.

So what you write is all a bit confusing?


An Alternator correctly sized for the load will not vary the voltage and supply 14.4v to the habitation bank from 'Start-Up', even if the Starter battery is 25% discharged. A good Starter battery will rarely draw more than about 15amps, even when quite low, so you can see it's impact isn't going to be significant.

Only if poor design or a fault exists will the Starter battery have any impact on the Habitation battery bank. 
Usually a 120amp Alternator is sufficient if all is correctly designed and installed, although it rarely ever is. 
Just look at the cabling runs, wiring thickness, number of connectors and Fridge operation on a typical Sargent EC500, it is woeful.
  
The major reason for high voltage drop, apart from excessive loading from a big battery bank, is usually the Fridge wiring. Few Converters take it directly from the Alternator which is the actual source of power for the Fridge.
As a result the load at the habitation battery means voltage drop, and obviously poor charging will result even on a new van.
Taking the Fridge feed from where it should taken makes a huge difference.

All covered in our web pages "Add a second Battery" : http://www.aandncaravanservices.co.uk/add-a-second-battery.php

Paulmold wrote:As far as I know Warwick Duos were only supplied with one leisure battery so I think previous owner has fitted the second one.

That's interesting Paul thank you, do you know if they could have been fitted as an option by AS when ordered ? I guess the distributor could have done it too.

It's possible it could have been done by AS at build stage or after by them or by dealer, impossible to answer unless you have any receipt for the work.

For those who suffer insomnia and need help getting to sleep, this thread covers (and dispells) many myths on batteries and charging :
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It contains many counter arguments from true experts, most of which we hold our own against. Brambles for example is someone we hold in high regard.

When we first pointed out how awful most UK motorhomes were at charging on Alternator there was much defensive posturing.

One even went out of their way to 'Prove us wrong' using sophisticated data logging, then after the tests wrote, "all I can say is... lesson learned and point taken Allan,.......the voltage is a miserable 13.7-13.9V".

There isn’t really anywhere they could conveniently place one without loosing valuable storage. Just been out to the van to have a deco.  The current seats wouldn’t allow the space as the X250 and its predecessors did.

I thought that was an excellent article, loads of ideas for potential shortcomings.
 
 
 
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I’m starting to think, since we moved house, a shorter PVC would be an advantage. Having an expensive car I don’t use, I’m thinking of selling the car and the Warwick and using the money to buy shorter PVC and starting all over again making it Hook up Proof ! I have a relative with a Duetto which is universally loved by his family and it just about goes in an ordinary parking slot. A shame AS don’t build on Fords anymore.
 
 
 
PS, my test above was with an ordinary fridge switched on.

willconquerer wrote:13.8 Volts for me.

I will check mine next week.  My experience with two service batteries,and reading these interesting threads, leads me to think one large service  battery is better than 2 smaller ones.
Or course a solar panel is still a worthwhile adition.

Micky

mikethebike wrote:

willconquerer wrote:13.8 Volts for me.

I will check mine next week.  My experience with two service batteries,and reading these interesting threads, leads me to think one large service  battery is better than 2 smaller ones.
Or course a solar panel is still a worthwhile adition.

Micky

Micky, this exact same thing was raised on another Forum and we replied :-


I would tend to believe one large battery of the same Ah rating surviving longer than 2 smaller ones if the battery is heavily used for high discharges, but I have never seen any evidence that states why. 

My own theory is that a large battery 'case' allows better flow of the Acid by Convection around the battery plates, keeping the plates in a a big battery cooler. Temperature is a battery killer. 

But I also think that smaller solutions rarely have a balanced battery pair. 
It has been reported before on this forum, that battery retailers are not always careful to send out batteries from the same batch. 
Often the cabling leaves something to be desired as well 

Only Alpha Batteries seem to be aware of just how critical the issue is and guarantee to send out matched batteries when ordered in pairs. 
Two 90Ah batteies of about 53bs/24 kg are heavy. One large 180Ah battery is really heavy and awkward to manhandle into and out of location.

AllaFEvans wrote:

mikethebike wrote:

willconquerer wrote:13.8 Volts for me.

I will check mine next week.  My experience with two service batteries,and reading these interesting threads, leads me to think one large service  battery is better than 2 smaller ones.
Or course a solar panel is still a worthwhile adition.

Micky

Micky, this exact same thing was raised on another Forum and we replied :-


I would tend to believe one large battery of the same Ah rating surviving longer than 2 smaller ones if the battery is heavily used for high discharges, but I have never seen any evidence that states why. 



My own theory is that a large battery 'case' allows better flow of the Acid by Convection around the battery plates, keeping the plates in a a big battery cooler. Temperature is a battery killer. 

But I also think that smaller solutions rarely have a balanced battery pair. 
It has been reported before on this forum, that battery retailers are not always careful to send out batteries from the same batch. 
Often the cabling leaves something to be desired as well 

Only Alpha Batteries seem to be aware of just how critical the issue is and guarantee to send out matched batteries when ordered in pairs. 
Two 90Ah batteies of about 53bs/24 kg are heavy. One large 180Ah battery is really heavy and awkward to manhandle into and out of location.

thanks. i was not thinking or the weight,but mine were low down outside locker.Previous owner had replaced one battery.Coupled with the poor wiring connections and different length of  circuits meant they were never matched.
Many owners will only change one if one is faulty.
Micky

Here's what you do if you fit a second battery, this will be complex..............
1. You add 25 to 30Kg to the payload weight of the vehicle
2. You lose the volume of the battery as spare space, already somewhat limited
3. I could go on and on..............

There is, however, a much simpler and more elegant solution........

Put as many solar panels on the roof as there is roof area, only use glued on semi flexible ones, Google, Photonic universe as an example.......

Mine is 150w, only one battery, virtually never use EHU, don't need to.

Total weight of my installation....................6Kg. never had a battery low voltage issue!!!

That's a great plan, but do you go camping in the winter months, do you manage then too, off hookup ?

willconquerer wrote:That's a great plan, but do you go camping in the winter months, do you manage then too, off hookup ?

Yes to both, we only do pubstops in the UK, recently (very) had 2 consecutive nights in Staffordshire, Outside temp 1.9C in the morning, ran the heating all night, LB voltage was 12.6 in the morning, fully recharged by early afternoon.

Weather wasn't great, but, in fairness, not that cloudy, also we drove 8 miles each way each day, so a total of 32 miles so the alternator did some of it.

Most people don't consider weight, my background is aviation and, surprisingly, under water engineering, both are weight vital.

We weighed our Warwick Duo before our last epic, full fuel, full water, full gas, all clothes etc, loo flush tank full, wifey in pax seat, 3200Kg, so 300Kg payload left available.

Hope this helps!

IanH

Interesting reading from all. I have to thank Willconquerer for re opening a most valuable thread. 
AllaFEvans thank you for such invaluable, technical, yet simply described information so us lay people can understand it. Appreciate your valuable time taken to persist in showing a different way of operation not written in a manual but with proof from real life experience.
I agree with bikeralw on locking the second battery thread was not helpful to forum members like me. Without this new thread, members would not have gained a bit more knowledge and understanding of alternative ways for battery installations. 

Paul O

willconquerer wrote:That's a great plan, but do you go camping in the winter months, do you manage then too, off hookup ?

A bit of thread drift but i think You mean more than a weekend!!Cannot remember how many weekends i have done in winter with only one battery and no solar panel.Never had a problem and never  had to run the engine.
Its when you go for a week or more,or never start the engine, that extra battery power becomes important in winter.
ie snow on your solar panel as well.

Micky

IanH wrote:Here's what you do if you fit a second battery, this will be complex..............
1. You add 25 to 30Kg to the payload weight of the vehicle
2. You lose the volume of the battery as spare space, already somewhat limited
3. I could go on and on..............

There is, however, a much simpler and more elegant solution........

Put as many solar panels on the roof as there is roof area, only use glued on semi flexible ones, Google, Photonic universe as an example.......

Mine is 150w, only one battery, virtually never use EHU, don't need to.

Total weight of my installation....................6Kg. never had a battery low voltage issue!!!

Ianh, The Issue with a single battery and 150w Solar is that your battery will be unable to store the amount of Solar you can harvest in Summer, hence wasting quite a few amps.
In mid June a really good 150w Solar solution in Cornwall can harvest up to 90 Ah, but a single 100Ah battery with a typical discharge to 50% Depth Of Discharge (DOD) can only store 50Ah, potentially resulting in 40Ah wasted energy.

That also means that the battery is likely to be discharged deeply for those 50Ah drawn out of the battery, resulting in significantly shorter life versus the same battery discharged by 30% DOD (70% charge still remaining).
Having a twin 100Ah battery set-up in the same 50Ah draw scenario will result in each battery being discharged to just 25% DOD, giving double the typical battery life.

Obviously the same twin battery set-up can be safely discharged to a greater 90Ah across the two batteries, if required, with the Solar still charging it up in June.


In mid December it's a different picture, a 150w setup typically harvests about 6 Ah a day, so obviously not much value, unless you discharge the battery very, very low which will not only majorly shorten the batteries life but create strain on the charging systems as the battery degrades.


 
Adding a second battery has long been understood as a one of the best ways of utilising the power available, but only if you stay within limits and the vehicle can support that change. 

Ian, If you do add a second battery, then clearly 2 x 110Ah poor quality budget Platinum batteries at a 'real' 240Ah loading on a 10amp Sargent or BCA charger, is not the same as 2 quality, high efficiency Varta LFD90 batteries placing a 'real' comparable load of 160Ah. 
That is a real world 80Ah difference in loading between choosing the worst batteries and the best.

So the batteries you choose are almost as crucial as any thing else. Please don't make the mistake of thinking they are anything like equal, the best batteries use technology that has advanced batteries to be up to 3 times better than the budgets that use technology from the 1980's.

Just have a look at the comparison between two batteries costing the same, one using advanced technology and one that clearly doesn't : http://www.aandncaravanservices.co.uk/battery-technology.php