Additional solar charging a caravan

Submitted: Monday, Jan 16, 2017 at 19:39
ThreadID: 134117 Views:3130 Replies:7 FollowUps:19
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I have recently purchased a caravan with a 240litre compressor fridge /freezer. The van has 2 x 120amp batteries charged by 300 watts of solar panels on the roof of the van...seems to work well.

But i would like to add more solar , so my question is ...i have 160 watts of solar panels on the vehicles roof rack .
So if i simply connect the 160 watts by anderson plug to the van will this assist the van ?

The panels on the vehicle have a mppt controller attached to the panels , do i need to bypass the mppt controller and feed the higher voltage into the van or just plug the panels output after the controller into the van.?

The van has a 40 amp controller.

Any suggestions please.
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Reply By: Batt's - Monday, Jan 16, 2017 at 20:33

Monday, Jan 16, 2017 at 20:33
My 40amp Redarc can handle 750w more is ok but of no use on peak days just wasted power supply. Check what brand your charger is and search it's max input.
I think it would be better to run all of the panels wired up correctly to the same input side of the charger. If I understand what your saying you would like to try and plug the 160w panel it into the existing Anderson plug that is usually plugged into the car if so that may confuse the charger because your trying to supply power from both sides of the charger if you know what I mean and it will favour one of the so no benefit gained. I may be wrong though.
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Reply By: HKB Electronics - Monday, Jan 16, 2017 at 21:39

Monday, Jan 16, 2017 at 21:39
If the Anderson plug is connected directly to the vans batteries then you need to leave the vehicles mppt charger in place to regulate the voltage.

There may be some interaction between the controllers when the vans batteries approach a high SOC but generally it doesn't cause any major issue.

I have a similar setup except I use portable panels plugged into the cars solar controller.

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Follow Up By: Tim F3 - Tuesday, Jan 17, 2017 at 08:57

Tuesday, Jan 17, 2017 at 08:57
Thankyou for your advice
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Reply By: Member - Jolls64 - Monday, Jan 16, 2017 at 21:57

Monday, Jan 16, 2017 at 21:57
Hi Tim,

In order to provide sound advice we must understand the how the system is wired (or proposed to be wired); however, some general advice for consideration:

Wiring the panels in series with the existing panels may be feasible if they are of the same rating. In this case you would bypass the MPPT controller. The overall array would be limited to the current of the lowest panel but the theoretical voltage would equal the sum of all the outputs. You would then require one MPPT controller that can handle the input voltage and the current. The charger then regulates the power to meet the needs of the battery - you will need to ensure the input is within the charger's capability.

Wiring the panels in parallel will limit the overall output to the lowest voltage. In this case the MPPT would remain in use. If the panels are not matched in output you will again have an inefficient setup. The issues related to the charger mentioned above still apply.

I trust this gives you a start point. If you provide the specification of the panels, charger etc perhaps a more helpful answer could be provided.
AnswerID: 607649

Follow Up By: Tim F3 - Tuesday, Jan 17, 2017 at 08:52

Tuesday, Jan 17, 2017 at 08:52
Jolls thankyou for the reply..
The vehicle has 2 x 80 watt panels on the roofrack fixed. There is a mppt controller mounted on the panels the power then goes to 2 x 100 amp wet cell deep cycle batteries mounted in the rear of the vehicle (there are also 2 x wet cell batteries under the bonnet that are only used to run the engine ).

I can connect the anderson plug from the van to either direct to the vehicles solar panels (after the mppt controller giving roughly 13.6 volts ) OR connect to the auxillary batteries in the vehicle that are receiving charge from the panels.

The van has 3 x 100 watt panels fixed to the roof that feed into a " pro vista controller" and then feed to a 40 amp bp 400 electro battery controller .

I hope this clarifies my set up.
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Follow Up By: RMD - Tuesday, Jan 17, 2017 at 09:02

Tuesday, Jan 17, 2017 at 09:02
Jolls64

I think you mean PARALLEL and not in series. Any additional voltage resulting from a series connection may not be adviseable.

IS that all panels in series, OR, two in PARALLEL and one (vehicle panel) in series with them? Then a mismash of the system perhaps?
The current from two in parallel won't pass through one which is the series one in the line. It will act as a restrictor. Just having higher voltage isn't necessarily an advantage.
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Follow Up By: Member - Jolls64 - Tuesday, Jan 17, 2017 at 21:16

Tuesday, Jan 17, 2017 at 21:16
RMD,

I definitely meant series. I was trying to explain the different options that you have to play with. In short you can connect panels in series, parallel or you can also use a combination of the two. (Usually to ensure you stay under the capability of the MPPT and regulator).

No matter how you connect them the theoretical power is the same (Power equals Voltage x Current (P=VI)). So in a parallel situation you are dealing with the lowest voltage of the combination and the combined current; in series the lowest current and the combined voltage; this plays out for each part of the circuit in a combination setup.

A little off the track; but, the panels themselves are usually cells in series and if you put the panels in series you create a string. Strings in parallel create an array. So with a little understanding of the electrickery you can work up a solution to meet your needs.

The key to whatever you create is having an appropriately matched MPPT (or two) and a regulator that can handle the input voltage/current of the string or array.

This is all theoretical and there are losses to be considered but it should provide a reasonable theoretical background to start from.
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Follow Up By: Member - Jolls64 - Tuesday, Jan 17, 2017 at 21:28

Tuesday, Jan 17, 2017 at 21:28
Tim,

I trust I did not confuse you -just trying to explain the theory so you can make an informed decision. There is plenty of pretty accurate information that has been added to the discussion. For mine connecting the batteries in parallel would probably be the best solution - that way you can power both sets independently and increase the run time of your setup as you are theoretically adding the available amp hours.
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Jan 17, 2017 at 21:58

Tuesday, Jan 17, 2017 at 21:58
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Well Jolls, you certainly confused me!!!! lol
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Allan

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Reply By: MEMBER - Darian, SA - Monday, Jan 16, 2017 at 22:32

Monday, Jan 16, 2017 at 22:32
Just a quick comment on supporting solar panels...there is virtue in having them portable, in that you can site them ideally to pick up the sun early and late in the day as well. As for the feed in...I'm no electrotech, but on my van, the builder installed an aux solar jack on the side of the van...it goes direct to the solar controller that looks after the vans two panels. So, my portable 100W panel and the two roof panels all feed just the one controller. Good luck with it all.
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Reply By: Member - Blue M - Tuesday, Jan 17, 2017 at 04:19

Tuesday, Jan 17, 2017 at 04:19
Tim, I have a 175litre compressor fridge in my van as well, so the set up is almost the same.

On the roof of the van I have 3x140w solar panels that runs through a Morningstar 30amp PWM controller that feeds the 3x120ah agm batterys within the van.

I have 2x150w solar panels on the canopy of my ute that are wired through a RedArc 40amp dc-dc MPPT charger that feeds 2x120ah agm batterys in the canopy.

The 2 batterys in the ute are hooked up to the 3 batterys in the van via an anderson plug.

Like you, I thought having two regulators and of different types would cause a problem.
I have recently completed a 6 month trip about the place and have had no problems so far.

I believe that hooking them up this way enables you to draw from all batterys, the charging side of it sorts it's self out. It maybe not the most effective way to do it, as I am sure there would be other more complicated ways to do it, but this way has worked fine for me.

Cheers
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Follow Up By: Tim F3 - Tuesday, Jan 17, 2017 at 08:56

Tuesday, Jan 17, 2017 at 08:56
Thankyou blue m
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Reply By: Shaker - Tuesday, Jan 17, 2017 at 12:25

Tuesday, Jan 17, 2017 at 12:25
I was under the impression that all panels had to go through only one solar controller.

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Reply By: Allan B (Member, SunCoast) - Tuesday, Jan 17, 2017 at 12:43

Tuesday, Jan 17, 2017 at 12:43
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Hi Tim,

There is some good information above, but I will try to put the complete issue to you.

Solar modules are typically rated as say "12 volts" which indicates the system voltage that they are to be used on. However they actually output higher voltages in operation and the connected controllers regulate the voltage to suit the battery needs.

CONNECTING PANELS IN PARALLEL:
Differing brands and models of solar panels produce differing output voltages so it is necessary to match panels of similar voltage characteristics if they are to be connected in parallel. Modules of significant higher voltage will overcome those of lower voltage such that they will not contribute.
In your case, you would need to determine the specifications of your panels in order to consider this proposition. However, if the panels are properly matched, this is a good method of increasing the harvest. Just ensure that the controller can handle the current.

CONNECTING PANELS IN SERIES:
This is essentially a "chain" and its strength is in the "weakest link". So the maximum power that can be delivered from panels in series is limited to the rating of the lowest module. In your case, the van panels of 300W would be limited by the vehicle-mounted panels of 160W. The voltage has been doubled but the current has been limited so there is no effective gain. The controller would need to be able to accept the increased voltage.
Furthermore, the vehicle battery is then left without a charging source.

CONNECTING THE CONTROLLER OUTPUTS IN PARALLEL:
If the output of the vehicle solar controller were to be isolated from the vehicle battery and then connected in parallel with the van controller there is a likely hood of undesirable interaction between the controllers upsetting the charging process.
The vehicle battery is then left without a charging source.
Not a recommended option.

CONNECTING THE BATTERY BANKS IN PARALLEL:
If the vehicle and van battery banks were simply connected in parallel, each with their own controllers in place then this would possibly be OK as the impedance of the cabling between the two banks would probably overcome any controller interaction issues. But little would be gained overall.

My recommendation is to leave the system as it is. Your proposition would be to complicate the system without benefit. You do say that it currently "seems to work well". If you wish to add more solar collection you would do well to add more panels to the van, either in series or parallel but with careful panel selection and consideration of the controller current capacity.

Incidentally, the "electro battery controller" you refer to is a device to protect the battery from over-discharge and plays no part in the solar charging.
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Allan

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Follow Up By: RMD - Tuesday, Jan 17, 2017 at 12:57

Tuesday, Jan 17, 2017 at 12:57
Allan. Do you think panels of closely but differing voltages can be used in a parallel circuit because when the regulator is operating it is dragging the panels down to just above battery voltage and therefore allowing the current flow because the panels are trying to rise in voltage but the PD means they all deliver current at that locked down voltage. Perhaps not ideal flow or max from som epanels but reasonable use of them just the same.
Interested in your reply.

Regards.
Ross
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Jan 17, 2017 at 13:32

Tuesday, Jan 17, 2017 at 13:32
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Yes certainly they can Ross. The solar modules have impedance and as you say, in operation the output voltage will drop so that the contribution from parallel panels is somewhat equalised. The degree of equalisation depends on the relative impedances and voltages so the closer the panel specs are then the better equalisation. As a guess I'd suggest that voltages of within 10% would be reasonable, but then it also depends on the panel impedances (read wattage ratings).
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Allan

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Follow Up By: RMD - Tuesday, Jan 17, 2017 at 14:57

Tuesday, Jan 17, 2017 at 14:57
Thanks Allan (EDIT) Sorry, forgot Roz

Regards
Ross
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Follow Up By: Tim F3 - Tuesday, Jan 17, 2017 at 15:24

Tuesday, Jan 17, 2017 at 15:24
Thanks to both ross and allen for your replies.
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Follow Up By: Tim F3 - Tuesday, Jan 17, 2017 at 15:33

Tuesday, Jan 17, 2017 at 15:33
Allen

if i simply connect the 2 charged batteries in the vehicle (after disconnecting the 160 watt panels ) in parallel to the vans batteries would i not get a longer run time of the fridge as it could draw on 4 batteries ?
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Jan 17, 2017 at 17:19

Tuesday, Jan 17, 2017 at 17:19
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Yes Tim, you could parallel the batteries to provide longer run time.
In fact you could probably do so without disconnecting the 160W panels as I have suggested above. It can certainly do no harm to try that. Simply connect the vehicle batteries to the van batteries with 6 B&S (13mm2) cable via 50A Anderson plugs. Be sure to fit fuses (30A) to the cable at each battery. Doing it this way will allow the 160W panels to continue to charge the vehicle batteries.

What load(s) are the vehicle auxiliary batteries currently supplying?
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Allan

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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Jan 17, 2017 at 17:27

Tuesday, Jan 17, 2017 at 17:27
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Further to my Followup 351 above, the majority of the solar panels on the market have reasonably similar electrical characteristics so can be paralleled with existing (same class) panels without problems and many users would have done so.
However mismatching may not obtain near-full performance. It is best to endeavour to obtain the best possible match to perform as you might wish.
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Allan

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Follow Up By: Tim F3 - Tuesday, Jan 17, 2017 at 19:10

Tuesday, Jan 17, 2017 at 19:10
Allan , the aux batteries in the vehicle mainly run a 60 litre everkool fridge/freezer constantly (freezer set to around minus 10 c ,fridge section has nice cold beer etc ) and other odds and ends occaisonally eg hf radio , 600watt inverter , led camp lights , charge phone and computer .

Thankyou for sharing your knowledge with the forum.
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Jan 17, 2017 at 19:19

Tuesday, Jan 17, 2017 at 19:19
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Tim, with that load your 160 Watts of solar input on the vehicle may not always have a lot of excess capacity to export to the van, but if the two battery banks are simply connected together it should sort itself out for the optimum result.
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Allan

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Follow Up By: Tim F3 - Tuesday, Jan 17, 2017 at 19:35

Tuesday, Jan 17, 2017 at 19:35
Yes , thankyou
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Follow Up By: Tim F3 - Tuesday, Jan 17, 2017 at 22:21

Tuesday, Jan 17, 2017 at 22:21
Allan as a sugestion how i may increase run time of the 240 litre fridge in the van and also run my 60 litte fridge how about the following.....

Have the 160 watt panels on the vehicle charge the auxillary 2 x 100 amp batteries in the vehicle connect this in parrallel to the van 2 x 120 amp batteries to run the 240 litre fridge.

Then have the 60 litre fridge /freezer connected to the 2 batteries running the ignition for the vehicle with a low voltage cut out set above a critical level that starts the vehicle.

Then when the vehicle is started it preferentially charges both start batteries before sending excess charge to the 2 x 100 amp deep cycle batteries in the rear of the vechle and then to the caravan as required..

Your thoughts please...
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Follow Up By: Allan B (Member, SunCoast) - Tuesday, Jan 17, 2017 at 23:08

Tuesday, Jan 17, 2017 at 23:08
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Tim, certainly that would work electrically. But it is not what I would like.
I am apprehensive about drawing fridge load from the cranking batteries when standing, even if they are 'protected' by a low-voltage cutout. I travel very remote and alone so well maintained crank batteries are precious to me.
Furthermore, crank batteries are not designed to be discharged very far at all. They are intended to supply very high current for a very brief period. Discharging them to depth shortens their life.

However, it could be useful to introduce your vehicle alternator into the auxiliary battery arena. You could connect the vehicle and van auxiliary batteries in parallel and feed your alternator to the vehicle aux battery via a smart isolator. The alternator will contribute charge to the entire aux battery bank although just how much reaches the van will depend on voltage drop along the way. It also depends on the output voltage of the alternator. If you have two cranking batteries it sounds like you maybe drive a 200 series and its alternator output voltage may not be high enough without taking special complex solutions.

By the way, the concept that the alternator will "preferentially charge both start batteries before "sending excess on" is popular but erroneous. What actually happens is that upon engine start, the alternator applies charge to the start batteries and within a few seconds their terminal voltage rises to the point of activating the 'smart' isolator. The alternator is now supplying charge to all connected batteries simultaneously and they each draw current according to their state of discharge.
Cheers
Allan

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