Off Grid Battery and Solar

[Foxy]

First post, so please be gentle!!

This has all probably been done to death loads of times, but searching through the forum, I couldn’t find the answers I’m looking for!
Probably like many people, we’ve left bookings a little late so, we’ve ended up booking on a few sites over the summer without EHU. Mostly long weekends, the longest trip being 10 days.
I have a 2017 Swift van with command, 100Ah battery and 110W solar panel. All LED lighting etc.

1) Is there an easy way of checking the capacity of the battery? I (rightly or wrongly) leave the 12v system on all the time and monitor it through the command system. The lowest voltage I’ve seen over the winter has been 12.1v, likely when the panel was covered in snow! Subsequently it looks to have recovered, and is now settling around the 12.7/12.8v mark when I check in the history. I did notice last year that the voltage seems to drop quite quickly with the radio, fridge and some lights on. Also, even with a full charge the Reich (quad) motor mover remote indicates low battery very quickly.

2) I have a family with quite high power demands! If the existing battery is duff, I’d likely change it to a 110Ah, or the largest I can fit in the box. my research shows there are a number of different battery types available nowadays what is the best, bang per buck?

3)To ensure the battery gets the best chance of getting fully charged during the day, is it worth fitting another solar panel? There also seems to be some discussion on weather a dual panel set-up should be in parallel or series. Anyone have any real world experience of a dual setup and what did you do?

I’ll be making sure I have plenty of gas with us for the fridge and hot water, is there anything else you’d recommend or things to be aware of while off grid?

 

[Buckman]

I may be wrong but I doubt if changing from 100ah to 110ah will make much of a difference. Also bear in mind that the UK is not always sunny every day during the summer. Also 12.7/8 seems a bit on the low side.
We have a 100w panel and a 100ah battery in our Buccaneer and on sunny days it will read as high as 14.8. Yesterday at 17.34hours the reading was 13.4. What sort of power do you think you will be using i.e. TVs, laptops etc?

 

[Foxy]

changing from 100ah to 110ah will make much of a difference

Understand, but if the existing battery is goosed, 110Ah could be a massive difference!

Also 12.7/8 seems a bit on the low side

Exactly my thoughts, makes me think that I’ve managed to get a good 3 years from it!
The battery was reading 13.1 last night, 14.4 during the day - solar must be doing something, just question the battery’s ability to hold its charge.

What sort of power do you think you will be using i.e. TVs, laptops etc?

All the above! I’m self employed unfortunately so I can’t get away from it completely. The kids also have their demands too, but it’s normally ‘managed’ while we’re away!

 

[Buckman]

As a matter of interest what caravan do you have and what sort of battery? A battery should last a lot longer than 3 years. If it was reading 13.1 last night, 14.4 during the day TBH I think it is okay. If the towing vehicle does not have a Smart alternator maybe consider getting a second 110ah battery. Then when out and about with the battery connected to the car 12v it can be charged.

However before going to the extra expense why not contact the sites without EHU and ask if they have battery charging facilities. Many of them have this facility generally free of charge.

 

[otherclive]

I’d be very surprised if at that age the battery is US. Also as Buckman says going from 100 am hr to 110 amp hr really would bring little practical benefit. I’d only do that if a battery change was required but even then the variation between two battery makes could make the 10 am hr gain difficult to see. If you really want to be able to maximise cam hrs for regular off grid use there are lithium batteries. Far lighter and smaller than lead acid or gel, but not cheap.

 

[JTQ]

Question 1) There is no easy way of checking a battery's holding capacity, however it becomes pretty obvious if it becomes low.

The holding capacity, the amount of energy it holds and can yield, drops as its life slips away, however the voltage of a fully charged but way depleted holding capacity battery is much the same as a new or any level of “aged” battery.

Most modern technology batteries when fully charged and no longer being charged will settle to 12.7 to 12.9, older technology ones a little lower.

However, it is very important to note this is after being charged and also after losing an extra bit of voltage a recently charged battery holds onto for some hours after coming off charge.

Therefore, seeing 12.8 volts during hours of lightness where the solar is or has recently pushed energy at the battery can be meaningless in the context of knowing if the battery is fully charged or not.

If you got up before it got light (or have night time monitoring) and saw 12.8 volts it would be far more telling and indicate the battery is about as charged as it can be. Though as I said earlier that does not mean it has its full 100 Ah capacity, but its 100% full capacity it aged condition now can hold.

During the daytime as others have said expect to see quite higher voltages, in mine, odd peaks right into the 15 volts range, but more typically mid 14s. This proves the charging system is working, but also it hints it has to be because the battery is telling the solar controller it is not yet fully charged. Quality controllers can totally switch off charging a battery, if it knows the battery is fully charged and doing more will only speed the battery's ageing.

2) A battery suitable for off EHU use will never be “best bangs for your bucks”. Batteries with the right technology to best suit that type of use are never cheap to make, nor be shy on their lead content, so be unlikely to be cheap to buy or light weight. What is needed is something with a good deep cycling and traction duty performance, that will also have a good number of “cycles” rating. As said, they will not be cheap, think in terms of still £110 £120 for 100AH C20 rating, even with a healthy discount, for a “reasonable” one. The “best” will probably be nearer £200.

3) You can only put solar panels in series if the controller is designed for the resulting doubling of the panel array's output voltage. In practice this means using a controller featuring true MPPT [maximum power point tracking, technology]. Controllers of this sort can better exploit lower light conditions, a very useful feature in our application where our real-life challenges are not encountered on good sunny days but overcast days. You can't just double up panels of varying characteristics and hope for an arithmetical outcome, ideally much about the panels needs to be compatible.

IMO you can't get away with being profligate with you use of energy with our solar systems. If “you” are with such greedy things like TV screens, it will struggle. If the battery is taken down more than about 40% below being full it will fast age the battery even a quality battery; if the battery is just a relabelled starter technology one that accelerated ageing starts much earlier than the 40% down.

 

[Buckman]

Question 1) There is no easy way of checking a battery's holding capacity, however it becomes pretty obvious if it becomes low.

The holding capacity, the amount of energy it holds and can yield, drops as its life slips away, however the voltage of a fully charged but way depleted holding capacity battery is much the same as a new or any level of “aged” battery.

Most modern technology batteries when fully charged and no longer being charged will settle to 12.7 to 12.9, older technology ones a little lower.

However, it is very important to note this is after being charged and also after losing an extra bit of voltage a recently charged battery holds onto for some hours after coming off charge.

Therefore, seeing 12.8 volts during hours of lightness where the solar is or has recently pushed energy at the battery can be meaningless in the context of knowing if the battery is fully charged or not.

If you got up before it got light (or have night time monitoring) and saw 12.8 volts it would be far more telling and indicate the battery is about as charged as it can be. Though as I said earlier that does not mean it has its full 100 Ah capacity, but its 100% full capacity it aged condition now can hold.

During the daytime as others have said expect to see quite higher voltages, in mine, odd peaks right into the 15 volts range, but more typically mid 14s. This proves the charging system is working, but also it hints it has to be because the battery is telling the solar controller it is not yet fully charged. Quality controllers can totally switch off charging a battery, if it knows the battery is fully charged and doing more will only speed the battery's ageing.

2) A battery suitable for off EHU use will never be “best bangs for your bucks”. Batteries with the right technology to best suit that type of use are never cheap to make, nor be shy on their lead content, so be unlikely to be cheap to buy or light weight. What is needed is something with a good deep cycling and traction duty performance, that will also have a good number of “cycles” rating. As said, they will not be cheap, think in terms of still £110 £120 for 100AH C20 rating, even with a healthy discount, for a “reasonable” one. The “best” will probably be nearer £200.

3) You can only put solar panels in series if the controller is designed for the resulting doubling of the panel array's output voltage. In practice this means using a controller featuring true MPPT [maximum power point tracking, technology]. Controllers of this sort can better exploit lower light conditions, a very useful feature in our application where our real-life challenges are not encountered on good sunny days but overcast days. You can't just double up panels of varying characteristics and hope for an arithmetical outcome, ideally much about the panels needs to be compatible.

IMO you can't get away with being profligate with you use of energy with our solar systems. If “you” are with such greedy things like TV screens, it will struggle. If the battery is taken down more than about 40% below being full it will fast age the battery even a quality battery; if the battery is just a relabelled starter technology one that accelerated ageing starts much earlier than the 40% down.

AMG battery can drop down to 8v or lower and still recover which is why I asked about the type of battery.

 

[JTQ]

AMG battery can drop down to 8v or lower and still recover which is why I asked about the type of battery.

Yes, so can LA of other technologies, e.g. Gel and spiral, but none can without some damage, that degree of damage varying significantly with the technology of the battery's construction and the duration and of course depth of discharge.

 

[Buckman]

Yes, so can LA of other technologies, e.g. Gel and spiral, but none can without some damage, that degree of damage varying significantly with the technology of the battery's construction and the duration and of course depth of discharge.

In 2018 our AGM battery dropped down to about 6v and was liek that for about a week before I managed to get it recharged. We are still using it without issues.

 

[Raywood]

If the 100 w is not up to the job I would replace it with a model far bigger say 140w but even they have their limitations and I am afraid use of power hungry items has to be regulated whatever the protests you get.
A 110 ah battery will help a bit but the difference will not be that great but you need the top grade, they are graded A, B and C. Motor movers are greedy but if used for very short periods should not be a problem. I would get the caravan as near into position as you can before using it. The fridge should not run on the battery but gas. They use a lot of power and would flatten the battery very quickly the battery setting will normally only work when the caravan is attached to the car with the engine running.
You cab check the battery with an external meter but you should mot need to.

 

[Jcloughie]

3)To ensure the battery gets the best chance of getting fully charged during the day, is it worth fitting another solar panel? There also seems to be some discussion on weather a dual panel set-up should be in parallel or series. Anyone have any real world experience of a dual setup and what did you do?

Make enquiries with the caravan manufacturer or (often better), with the manufacturer of the solar system used in your van. If this is Sargent, they are extremely helpful.

I my case they could advise me on what maximum my system could monitor.

You may find you can safely add to your system without the need to up grade the whole system.

John

 

[Foxy]

As a matter of interest what caravan do you have and what sort of battery? A battery should last a lot longer than 3 years. If it was reading 13.1 last night, 14.4 during the day TBH I think it is okay. If the towing vehicle does not have a Smart alternator maybe consider getting a second 110ah battery. Then when out and about with the battery connected to the car 12v it can be charged.

However before going to the extra expense why not contact the sites without EHU and ask if they have battery charging facilities. Many of them have this facility generally free of charge.

I think that the sites I'm going to be visiting will likely have charging facilities, but I'd rather not have the hassle of taking it out and carrying it across the field! There will probably be situations in the future where that option won't be available.

 

[Buckman]

If the 100 w is not up to the job I would replace it with a model far bigger say 140w but even they have their limitations and I am afraid use of power hungry items has to be regulated whatever the protests you get.
A 110 ah battery will help a bit but the difference will not be that great but you need the top grade, they are graded A, B and C. Motor movers are greedy but if used for very short periods should not be a problem. I would get the caravan as near into position as you can before using it. The fridge should not run on the battery but gas. They use a lot of power and would flatten the battery very quickly the battery setting will normally only work when the caravan is attached to the car with the engine running.
You cab check the battery with an external meter but you should not need to.

Would a 110w solar panel be sufficient to charge up a 140ah battery completely?

 

[otherclive]

Would a 110w solar panel be sufficient to charge up a 140ah battery completely?

Raywood was proposing a 140 watt panel for a 110 amp hour battery.

 

[Buckman]

Raywood was proposing a 140 watt panel for a 110 amp hour battery.

I got mixed up there between battery and solar panel.

 

[Beachball]

Hi Foxy welcome to the forum

 

[Woodentop]

One thing often overlooked. Car batteries are rated at C/10, i.e. they will (OK, should) provide their rated capacity if depleted at a current draw of one-tenth of the rating, i.e. a 70Ah car battery should provide 7A for ten hours.
Leisure batteries are rated at C/20 so you need to pay significantly more attention to how much current you are drawing and what you can do to reduce it.
If you want to get a second battery always get a branded one is my advice. Having said that the HLB681 from Halfords is actually a badged Yuasa which is one of the best battery brands you can get.
As our battery is under floor we need a low profile and have a Varta LFD90 which is rated for both vehicle and leisure use although I cannot find what class. When we came back from a trip last October I didn't connect the mains and left the (100W) solar panel to look after it. A month or two later my wife went into the van and noticed that the alarm didn't work and nor did the interior lights. Check battery - 3.6V!! Neither of our smart chargers would even start so I tried the old fashioned way. I put a 21W flasher bulb in series with the output of a 13.8V 8A regulated power supply and connected it up. The bulb shone brightly at first but over about two days it gradually extinguished. Plate voltage now 9.4V. Left it for two days more, voltage now 11.5V so disconnected my PSU/lamp and replaced it with a smart charger - which worked! Left it two more days and it was fully charged. Today I have moved the caravan on the drive with the mover both to relocate the wheels to stop tyre flats, and to check and pump up the tyres. In total about 15 mins on the mover without a hiccup.
Last idea for the OP: have you ever considered getting a invertor generator such as those by Honda? Run very very quiet and (the one I'm thinking of) will supply 400W which should be enough to replace usage.

 

[ProfJohnL]

Hello Foxy,

Experience suggests that most caravans typically use less than 40Ah of battery capacity each day. That means if you can put that much back in by whatever means you will secure your 12V needs indefinitely. This also means that provided the battery is big enough to supply your daily needs, going any bigger offers no real benefit.

Most solar panel users find that 100 to 150W of panel is more than adequate.

 

[Raywood]

I think the problem here is that the OP has a family with power hungry things they want to keep charged, which suggests they may need rather more power than average. At the end of the day though they have to adjust their power usage to what is available.