Solar panel support

Hello,

I did not buy and install my solar panel system yet. My requirements are still the same as in my earlier post.

Since I am away from my OKA sometimes for several months I'd like to keep both batteries charged. I assume that it is not a good idea to connect both batteries parallel to the solar panel while away since the two batteries are of different type. Any idea for a good wiring to keep both batteries healthy? Do you recommend to charge one of the two batteries via a DC to DC charger like the CTEK brand? In this case I probably would have to disconnect the house battery from the existing OKA wiring via the relay?



I did look on the website and did only find one more topic related to solar panels: www.oka4wd.com/on-the-road/721-solar-pan...house-batteries#1432


I assume that the link in the earlier post to the solar installation of "David and Janet Ribbans, Oka 148" got lost with the move to the new website. Could you please post the link again?

OIA
Ideally you need an MPPT solar regulator connected to the largest battery and then a DC to DC charger to charge the second battery from the first/largest one.
It might possibly be cheaper to replace one of the batteries so you have two the same in parallel and then charge off the solar through the regulator. No need for the DC to DC charger then.
Never leave the solar connected to the battery without a regulator or closely monitoring voltages as you will damage the battery.
We run 500w of solar through a Plasmatronics regulator into 4x120aH AGM batteries for the house system in the Oka.
The Oka then has the standard main and auxilary batteries, the auxilary is charged via a Redarc VSR from the main battery.

OiA, yes the link to my Solar Panels article got lost in the transfer. The original link is here , but I've also converted it to a pdf document and uploaded it to the new website Technical Documents Library here (4.3mb).

Note that technology (eg solar regulators) and the availability of parts (panel shapes and sizes) has moved on in the 4 years since I built our system so some adaption would be required but the principles remain the same.

Regarding batteries of different types, as long as the batteries are the same technology (eg all lead acid, AGM or Gel) then paralleling them should not be a problem. Solar charging is generally less aggressive than an alternator could supply so there is less risk of damage, but a good regulator is essential anyway.

A CTEK dc-dc charger is not required for a solar installation since the solar panels already generate a charging voltage higher than the batteries need (hence the need for a regulator). A CTEK charger is beneficial in the absence of solar to boost the output from an alternator (which are pre-regulated down to 13.8v) for faster and more effective charging (the alternative is a smart alternator regulator), and obviously is only relevant when the engine is running.

One note about solar panels. Don't ever disconnect the batteries from the solar charger while they are charging. Unregulated solar panels can produce 20-30v which can damage any electronic equipment. The solar regulator might prevent this but why take the chance. An unregulated alternator could do the same damage but it's fairly obvious when an alternator is running whereas it's easy to overlook solar panels.

For the record, our Oka is laid up (outside) for several months over summer and the solar panels keep all three batteries fully charged without attention.

OIA - there is a device called trik-l-start - available from the USA - that is a 5 amp charger designed to keep the starter batteries topped up from the house batteries whenever the house batteries are themselves being charged from the solar. Cost about $45 plus postage.

Another option is something like Sunsaver duo solar regulator (that one is probably obsolete) which can handle more than one battery

OiA, it is all good and well to spend money on electronics to keep batteries charged up while the vehicle is stationary and unattended for several months, but good quality AGM batteries have a capacity loss of approx 1% per month (I have been told, but can not verify). Maybe that could be a first step. No need to install anything at all!
'Normal' lead acid batteries lose 5-20% of their capacity per month (depending what literature you believe). For reasons outside my control I had 2 AGM batteries sitting unused for 1 year. Terminal voltage was still 12.6 Volt, and each battery started the OKA first go! BTW the manufacturer states a shelf-life of 2 years.

If you were to install solarpanels at a later date, yes, as David said, they will keep your batteries 100% when using a solar regulator/controller. This is commonly connected to the auxilary battery (-ies).
And as you indicated, to charge all batteries, maybe connect the starter battery parallel then. Although if a fault would develop (which is unlikely), this could see you without power at all. Hehe, but likely you would not be in the bush then, and in the civilised world.

In regards to support of the large solarpanels: have you considered flexible solar panels? No need for any support, just stick them to the roof, they are only 1.5 to 5 mm thick. Less wind resistance, no vibration other than that of the roof itself, less likely to be damaged, some can be walked on! There is quite a range of suppliers and manufacturers.

Hank, you are quite right about variable self-discharge rates (I reckon the variation is 1% to 50% per month, depending on their age and condition), but unless the batteries are totally isolated from all other electrical devices, there will also be a small but measurable current drain anyway, due to things such as radios on standby, solar regulators (when there's no solar energy), remote controls, clocks, inverters on standby, alarm systems or even good old leakage through the wiring.

Batteries would prefer being at least float/trickle charged while on the shelf so I think it makes sense to have a standby charging system, then you have no worries on either count.

So, I got the CTEK D250S DUAL for a good deal here in the US!

- I currently have a pretty small starter/alternator battery installed in the OKA which supplies plenty of power to the starter motor.
- My auxiliary/service battery is a deep cycle 130Amp type.
- I am planning to cover the roof area above the two front seats (not the cabin area since I have a roof hatch installed) with solar panels.

I hope that the CTEK can do a couple of things:

1. Operating as a MPPT regulator for the new solar panel(s).
2. Charging the starter/alternator battery and auxiliary/service battery independently exactly to the requirements of each individual battery during the engine running via the alternator and solar panel(s).
3. Charging the starter/alternator battery and auxiliary/service battery independently exactly to the requirements of each individual battery during the engine is NOT running via the solar panel(s).

I have attached a sketch below how I do intend to include the CTEK into the existing OKA wiring. I think I will have to disconnect the charge relay otherwise the set up will only work while the alternator is not running (and the charge relay is open). According to the CTEK manual the charger has a "Built in battery guard for the starter battery".
But maybe it is wise to leave the override key switch in place so that I am still able to parallel the two batteries in the event I would need additional power for starting the engine?
I am worried that the CTEK unit might get damaged when the contacts "alternator battery +" and "service battery +" are connected via the override key switch?

I would appreciate your comments and ideas about the set up and wiring described.

OiA, I've had a look at the CTEK 250s Dual specs and wiring and my understanding is that it take its input from either:

• the starter battery (ie when being charged from the alternator). It then bumps up the voltage to charge the auxiliary battery(ies) (CTEK call them service batteries), or
• from the solar panels to charge the auxiliary battery, but only float charges the starter battery (this sounds wrong but if the starter battery is used only for starting the engine and is being charged by the alternator, then it shouldn't need further charging), or
• both alternator and solar, depending on the state of charge of the batteries.

In both cases it uses an MPPT 5 stage charger.

However if the auxiliary battery becomes fully charged the solar panels will then charge the starter battery if needed.

The maximum output of the CTEK unit is 20A, which includes the auxiliary battery charge current and the load it is supplying, otherwise you'll be running down the battery.

From all this I deduce 4 things:

• The CTEK charger won't do anything to improve the alternator performance and relies entirely on the alternator capacity and regulator settings (you would need a smart regulator, which could interfere with the CTEK operation, and/or larger alternator to improve charging capability).
• You won't need the charge relay in the circuit, the CTEK unit has that functionality built in. It could be left in place, but disconnected, in case of failure.
• The override key switch should be left in place since batteries can fail and you might need it. The CTEK unit does not have a manual paralleling capability (and it would need very heavy wiring if it did). This won't harm the CTEK unit since all you are doing are putting the 2 batteries in parallel so the CTEK unit simply sees 2 batteries with the same terminal voltage and would probably do nothing.
• If you have more than one auxiliary battery, you'd need some diode separation or a voltage sensing relay between them so they can charge in parallel but don't discharge each other overnight. The maximum recommended auxiliary battery capacity is 300AH.

BTW, don't use 24v solar panels, the CTEK input is limited to 22v which the maximum that most 12 v panels would supply.

Smartpass doesn't seem worth the extra money and is only beneficial if you have a large solar array (more than 20A capacity or around 280W) or need to regularly draw more than 20A from your auxiliary battery. It could be added later.

You can of course connect "accessories" to the starter battery but they should be low current or emergency type equipment (eg we connect our HF radio to the starter battery so it always has power when needed, just like the starter motor).

Here is a wiring diagram for a typical alternator/solar installation. It doesn't show the alternator connected to the starter battery:



There some useful websites on the CTEK 250S Dual installation but also a lot of misinformation. Reasonable ones seem to be:

Kampers.com

jtsonlin.com

carvans and motorhomes

go see australia (Pretty girl too)

Dear David,

thanks for that elaborated feedback which really helps!

Another question somebody might help me with, the size of the solar panels I have to buy. To cover the roof above the two front seats with panel(s) will supply me with sufficient power for my needs.
Since I am not at the vehicle to take measurements I wanted to find out if somebody could supply me with measurements of the surface as indicated in red in the sketch below?
Depending on the dimension of available panels I would probably need to install two or more panels to make maximum use of the surface.







I considered to install the panel(s) with special plastic brackets (picture below) which I could glue to the roof with Sikaflex. I then did remember that the surface is not flat, is that correct? I probably have to make a bracket and fix it to the roof rack and/or sun visor mounting bolts?




I would like to then be able to easily remove the panels from a bracket to move them into the sun while camping. Maybe the type of clips used to fix the dasboard into position would be appropriate?

OIA you should not mount them flat on any surface as they get too hot which lead to lower outputs. As you said too the roof is no where near flat enough. They need to be mounted so that there is airflow between the panels and the roof, I mounted two 125W panels side by side on the original roof bars which mount to the captive nuts in the sides of the turret. The just about cover the entire cabin roof and out over the back edge of the visor.
I bought them from Bit_Deals on ebay. They are 1100 x 808mm and about 35mm thick, weigh 11.2kgs each.
I would not bother with making them removeable, too high up to easily remove from the roof, they make a good tropical roof and keep the cab cooler. Panels are getting cheaper all the time, those particular panels are the same ones I bought two years ago, they are now half the price.

Here is the link to the ebay seller. 125w panel
They are good to deal with, lots of people on 4wd and motorhome forums have bought panels from them without any hassle.

OiA, agree with Peter, I would permanently mount them following the cabin roof line about 50mm above. I think 200-300W is plenty but it does depend on your electrical power needs and battery capacity.

The cabin roof appears to be only around 1m deep so you'll need to choose the panels carefully, they all vary in size (125w and 95w are 1100 or 1200mm long), but some overhang might be acceptable.

You could also consider more, lower power panels (eg 3 x 95w panels rather than 2 x 125W) since they would be stronger, easier to mount, with more redundancy and resistance to shading.

If you have a Jaycar or equivalent store in SA, they would have have plenty of mounting bracket options. I would recommend full length longitudinal mounting bars to reduce the effects of shock and vibration. I used lengths of angle ali and made some simple Z brackets to attach to the roof (sealed to stop ingress of water). Air flow under the panels is important for cooling.

If you need a removable panel, you could add one or 2 smaller, easier to store, 40w panels and lay them in the sun.

Hi,
Some of this stuff seems overly complicated.we have been on the road for 2.5 years with the system.It consists of an 80amp alternator which charges 520amps of house batteries thru a 100 amp redarc relay,The relay does allow an overide button so that in the event of failure with vehicle batteries you can use house to start.The relay doesnt cut in until the vehicle batteries are above 12.6 volts.In addition I have 520watts of solar charging thru a plasmatronic 40 regulator.We sit for extended periods at bush camps,but have had to use the generator a minimal number of times.This usually when the weather is extremely hot but it very cloudy.We run an electric upright waeco fridge and a waeco freezer,computers, sat. tv.and other devices as you would at home.The only addition we will get round to is a free standing 200watt panel for shaded locations,which will get a lot of use when we go back east.The solar panels are wired back to the regulator separately,so that should a panel fail we still have some power.

We run four 125w panels charging 480ah of batteries, we don't charge the batteries from the vehicle at all and in over 2 years they have never fallen below 60% capacity. We use a 1000w 240v electric jug, normal Sunbeam toaster and a single inductive cooktop occasionally through the inverter. All LED lighting is 12v as is the 130l fridge, cooking is done on a diesel cooktop and diesel supplies hot water and central heating. We have no gas. Occasionally when there is an excess of solar we have switched the 240 element on in the HWS instead of using diesel.
We also have all the usual stuff that needs charging like laptops, printer, kindles, phones, broadband modem etc etc. On the very rare occasions we want TV we use a dongle in one of the laptops but do occasionally watch DVD's or movies on the laptop.

I was a bit concerned at the lack of rigidity of the panels for mounting flat in an application that was going to cop sustained severe hammering from driving over corrugations, so I used several pieces of 'noodle' as supporting columns - cut to slightly more than the distance between the underside of the panel and the roof. This dampens the movement of the panel plus slightly domes the panel instead of its normal saucer shape so water doesn't collect.

We have 2 x 180W (I think) and there were times when stationary for a few days when it couldn't quite keep up with all the junk we run, so I'll be adding an extra panel now the price has come down so much.

Thanks for your feedback!
I am not able to take measurements on my OKA now. Anybody there who could help me with measurements of the surface as indicated in red in the sketch above?

Thanks so much ...

OiA - on my XT the width is 1720 and the length is 1130 for your red markings.

1120 deep x 1730 wide on LT 266

Thanks a lot for the measurements of the roof area!

Tony Lee,
looking at your set up on picasaweb.google.com/1146117281102541343...#5600904487100886354 I was wondering if you have a close up pictures of your bracket and fitting of the front solar panel? Looks like your panel is close to to roof but still has enough air flow between roof and panel.

Thanks a lot for the measurements of the roof area!

Tony Lee,
looking at your set up on picasaweb.google.com/1146117281102541343...#5600904487100886354 I was wondering if you have a close up pictures of your bracket and fitting of the front solar panel? What are the dimensions of your front panel?
Looks like your panel is close to to roof but still has enough air flow between roof and panel.