Camper Trailer Battery

Submitted: Saturday, Jan 07, 2012 at 20:48
ThreadID: 91075 Views:2586 Replies:4 FollowUps:9
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Hi all hope you enjoyed your Christmas & New Year.

I have a Offroad Camper with a Supercharge Allrounder Battery 105amp hour installed, this battery operates 1 x 50lt Weaco and 1 x 35Lt plus LED lights at night. Connected to the battery is 2 x80Watt solar panels in series giving 24volt.
Question the current battery is 27months old and needs replacing as the recovery time is slipping and won't take full charge. We are going on a trip to the centre of Australia in April and would like a reliable deep cylce battery. I am disppointed with the supercharge duability.
Could I have some advice on which battery would be suitable.

Thank You in advance to all who reply.

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Reply By: Mick O - Saturday, Jan 07, 2012 at 21:35

Saturday, Jan 07, 2012 at 21:35

I am using a Powersonic AGM's at the present and have found them to be excellent but they are a few more $ than other AGM's.

I was a little worried about your panels being wired in series to provide 24 volts when you have a 12 volt battery. Have I missed something. Normally with a 12V system (and I'm asuming your Supercharge is a 12V battery) you would wire panels in parallel, positive to positive to combine the amp ratings (Imp) of each panel together and the array voltage stays the same as a single panel. With 24 volts going into a 12V system, you may have cooked your battery as they should last longer than 27 months. What type of solar regulator are you using and are you getting DC (Vehicle) or AC input to the battery at any stage?

When you wire panels in series, positive to negative (this is also called a string of panels) you combine the voltage rating (Vmp so 12 + 12 = 24V) together and keep the Imp the same as one panel.

Sorry if I've missed something.

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trip would doubtless be attended with much hardship.''
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Reply By: Battery Value Pty Ltd - Saturday, Jan 07, 2012 at 21:43

Saturday, Jan 07, 2012 at 21:43
Hi Allan,

I have to admiit to having read your post 2 or 3 times in search of a reason why you've the 2x12V panels connected in series for 24V to charge the 12V battery.
Doing so only gives you 4A peak charging current, or around 20Ah/day which is less than your fridge and lights will use.

To make sufficient solar power available you'd need a good solar regulator, preferably MPPT for max solar charging efficiency.
That way your 2x12V panels can remain in series, and the MPPT solar regulator ensures there'll be enough juice in the battery to power your loads.

We can certainly help you out with a good MPPT solar regulator and a quality deep cycle AGM battery, more information can be found by following the link to our profile below.

cheers, Peter
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Follow Up By: Member - Allan H (NSW) - Sunday, Jan 08, 2012 at 07:25

Sunday, Jan 08, 2012 at 07:25
Hi Peter,

Is there any advantage supplying 24 volt via 2 x 80 watt solar panels through a MPPT regulator to a 12 volt battery. What I am trying to acheive max power supply to the battery via the solar panels.

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Follow Up By: Battery Value Pty Ltd - Sunday, Jan 08, 2012 at 08:18

Sunday, Jan 08, 2012 at 08:18
Hi Allan,

yes, there are a couple of advantages having a 24V rated panel on the input of the true MPPT solar regulator.

The DC/DC converter inside the MPPT regulator works most efficiently (around 95%) for input voltages which are 2~3 times the output voltage.
E.g. if the battery was sitting on 13V during charging, then the optimum input voltage band would be 26~39V. So this coincides nicely with the max power voltage of a 24V panel which is somewhere between 32 and 36V.

The second advantage is a 50% voltage drop reduction in the panel wires.
That's because power equals voltage times current. So for constant power, but double the voltage, the current drops to half.
In your situation the max solar panel current drops from ~8A down to ~4A when you configure the panels in series instead of parallel.

You can select cheap 3mm (rated 10A, 1.13mm squ) auto wire for this.
At full insolation, this wire pair only dissipates about 0.5W of power per metre of distance between solar panel and regulator. Because full insolation usually is only achieved for short periods, the average power loss is less than that.

Any more questions, just get in touch with us using the links provided below.

regards, Peter
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Follow Up By: Member - John and Val - Sunday, Jan 08, 2012 at 08:18

Sunday, Jan 08, 2012 at 08:18

There is advantage in running the panels in series provided you are using a suitable MPPT controller and it is mounted at the battery, not at the panels. With the 2 panels connected in series, the voltage is doubled, if in parallel the current is doubled. Losses in wiring leading to the battery are proportional to the square of the current, so doubling the current quadruples the losses. These losses may be negligible if the wiring is short and uses heavy wire.

A suitable MPPT controller such as Peter suggests will convert the available voltage to that required by the battery, effectively swapping any excess voltage for extra current, and allowing the panels to operate at their maximum output. It is important that wiring losses between controller and battery be minimised, so that the controller can deliver the optimum charge regime at the battery.

In your case, as others have said, the controller must also be capable of delivering the higher voltage (>15) required for your calcium doped battery. The voltage from the alternator will almost certainly not be high enough to fully charge a calcium battery.

I'd be a bit doubtful that your present panels and battery could handle the 2 fridges and other camp needs. Perhaps the present battery has suffered as a result? I've added a dc-dc charger to our rig (200 Ah storage, 160W panels, 1 fridge etc) and find it excellent. If you can accommodate a second battery, suggest two cheap 100Ah ones in parallel might be better than one expensive 100 Ah one. Add a 20 or 30 amp dc-dc charger and all electrical problems solved!



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Follow Up By: Member - Allan H (NSW) - Sunday, Jan 08, 2012 at 08:53

Sunday, Jan 08, 2012 at 08:53
Excuse my lack of understanding.

You have suggested the ah drops from 8 to 4 ah in series, and if the fridges use 6 amps per hour wouldn't the battery go flat loosing 2 amp hour.But if it was hooked up in parallel you would be producing aprox 8-10 amps per hour therefor the battery would maintain charge? Very Confused.

If I did have x 100 amp batteries fitted would the panels be able to keep up the charge to the batteries?

Thanks heaps

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Follow Up By: Member - John and Val - Sunday, Jan 08, 2012 at 09:39

Sunday, Jan 08, 2012 at 09:39

There's a lot of confusion around this topic. You are not alone!

The rate of flow of electrical charge is measured in amps. In vehicle electrics we commonly express the total amount transferred in a a period of time (say an hour) as so many amphours.

An 80W panel in full sunlight will typically produce about 4 amps, so in one hour it can deliver to the battery about 4 amphours, or in a typical clear day with say 7 hours of sunshine, about 28 amp hours.

Meanwhile the fridges are cycling on and off, each drawing about 3 amps while running. If the fridge motors ran continuously they'd each consume about 3 amphours every hour. In fact the motors don't run continuously, they cut in and out and are probably only running about 1/3 of the time. The average over an hour is then about 1 amp each, so they are each consuming about 1 amphour every hour. If they do this for a day, the 2 fridges will require about 48 amphours. You have 2 solar panels, each providing (in this simplified hypothetical story) 28 amphours, which just covers the hypothetical requirements of the fridges, with a small margin.

The key to optimising your charge rate is the MPPT controller. This device takes the available energy and converts it so that the panels operate at their optimum and also provide optimum charging conditions for the battery. This is achieved by converting voltages. Each of your panels operates best when delivering about 17 volts. The battery requires around 15V. The controller trades those excess volts for additional current. With your 2 panels in series, they'll deliver about 34V and again an MPPT controller will convert this to 15V and trade the excess for extra current.

A non-MPPT controller does not have this voltage conversion ability. Such controllers simply pass on whatever current (amps) is available from the panels. Here, two panels should be in parallel so that their current, rather than voltage, is doubled.

Hope that makes sense. You may find Electricity for Camping a useful read.



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Follow Up By: Member - Allan H (NSW) - Sunday, Jan 08, 2012 at 09:50

Sunday, Jan 08, 2012 at 09:50
Thanks John for you patience,

Now I can understand why you would have the panels in series.

Would the system benefit from 2 x 100 amp batteries ? as I do have space to sit another battery alongside the other. Would the solar panels keep up the charge to both batteries ?

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Follow Up By: Battery Value Pty Ltd - Sunday, Jan 08, 2012 at 10:09

Sunday, Jan 08, 2012 at 10:09

as John explained it already, just a few more words finishes the lecture for today ;)

What makes all things electrical tick is power, which is the product of current and voltage.

A true MPPT solar regulator can transform the incoming current (solar panel current) to a higher outgoing current (battery charging current).
The transformation factor is the ratio incoming voltage/outgoing voltage.

E.g. for a panel current of 4A, and an in/out voltage ratio of 2.5 (solar panel working voltage of 35V, battery charging voltage 14V), the battery charging current would be 10A.

And yes, the solar panels will keep up the charge on an even greater number of batteries.
But whether this will work or not, really depends on the amount of solar power coming in, versus the amount of power the loads consume.
The batteries merely act as energy storage for times when there's no solar coming in.
And yes, 2 smaller batteries in parallel are always better than just the one (or just one big one), for a number of reasons:
Less depth of discharge when keeping all other things equal (this results in longer battery life).
More batteries are less likely to experience excessive charging currents when used in connection with an alternator.
A more balanced weight distribution.
More vibration/shock resistance of two smaller batteries compared to one large one.
Cheaper shipping rates of smaller batteries - couriers won't charge excess weight fees.
Easier handling during installation, better portability.

And most importantly, the energy storage capacity (Ah) increases which lets you ride out longer periods of little or no sun.

cheers, Peter

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Follow Up By: Member - Allan H (NSW) - Sunday, Jan 08, 2012 at 10:09

Sunday, Jan 08, 2012 at 10:09
Very good read John, I will be printing this article and locating this in my folder in the Cruiser.

I would recommend anyone with any questions to read this article first, Electricity and Camping could save yourself and others a great amount of time.

Tanks again
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Follow Up By: Member - John and Val - Sunday, Jan 08, 2012 at 11:37

Sunday, Jan 08, 2012 at 11:37

If you have space, I'd go for more storage capacity. Peter has outlined the advantages.

You ask if your panels can deal with the extra battery. Yes, a pair of batteries connected in parallel will simply act as a single battery with double the capacity - the increased capacity doesn't dictate increased charging requirements. BUT These requirements remain directly related to the energy balance. If you take more out of the batteries than you put in, obviously things will come unstuck! Having extra battery capacity gives you a bigger buffer. I think with your 160W of panels and 2 fridges your energy budget is pretty tight. As I mentioned, although we carry a similar amount of solar generating capacity, we fitted a dc-dc charger to provide better alternator charging. Coupled with 200 Ah of storage, this has been very satisfactory.

Thank you for your kind remarks concerning the blog. It was originally written specifically to answer the sorts of questions that come up here very often. That it has the highest hit rate of any EO blog indicates just how fraught this this electrical stuff is. It's overdue for a rewrite, but the fundamentals haven't changed.


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Reply By: Ross M - Saturday, Jan 07, 2012 at 21:50

Saturday, Jan 07, 2012 at 21:50
G'day Allan H
I have used Chinese made Full River batteries in a gell deep cycle configuration and they seem ok. I run a 40 engel and a waeco 35l as freezer.

I have the same wattage of panel 2 x 80w but arranged in parallel 12v to the regulator.
I also noticed you mentioned yours is in 24v.
I haven't tried it in 24, is there any advantage except the increased output as the darker hours approach.

From my experience just the 105ah is not much capacity as I use 1 x105ah & 1 x 120ah in parallel. The system can also be switched to the vehicle battery to top up and for use while travelling if need be.

Ross M
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Reply By: Member - Frank P (NSW) - Saturday, Jan 07, 2012 at 21:50

Saturday, Jan 07, 2012 at 21:50
G'day Allan,

I have one of those batteries as an under-bonnet auxilliary in my Prado. 4 years now and still ok, but I use a dc-dc charger that is programed to suit the battery (see below).

These are calcium-calcium batteries and need to be bulk charged up to about 15.2 volts before settling into absorption then float.

I'm not sure your 160 watts of solar will run your two fridges - others will advise on that.

But I think the main problem might be that your charging regime is not what the battery needs. All your chargers - mains, solar reg and dc-dc if you have one, need to be capable of charging the Allrounder to 15.2 volts (ie have a calcium setting on them)

If you're touring and don't get to mains power very often, a dc-dc smart charger with a calcium setting for your Allrounder is probably a necessity to give that battery a full charge while you drive.

If you're already set up with chargers and regulators for more conventional charging rules, try an AGM or a more conventional flooded wet cell deep cycle battery that needs maybe a conventional 14.4 volts or so before absorption and float.



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