Adding solar panel to dual battery system

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mgladwin

mgladwin

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Strathalbyn, South Australia
Hi people,
I have a redarc 100 amp sbi in my navara charging a 100ah agm battery in the tray. I have just acquired a 60W solar panel and want to know the best way of incorporating it into my current system.
Do I just get a solar charge controller and hook it up to the battery, or do I need to do it a different way. Would the alternator compete with the solar panel and stuff up the charge controller?
I have seen the ctek dual charger which works out the best source to charge from and i can just wire the solar panel straight up as the ctek does all the controlling.
I know this is the better option but seeing as I already have the sbi dual battery system installed I just wondered if there was a cheaper/ easier way.

The panel won't be permanently connected. Will only come out when we are in camp and set up. So a Plug and Play type setup.

I apologise if this post is all over the place as it was written on my phone.

Any help appreciated.

Cheers
Martin
 
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If the battery's a permanent installation then it should be charged by the car while you're driving around.

Once you're camped the car isn't running, so the solar panel won't be competing with anything.

If you hook both up directly to the battery I can't see any issue. You can't drive off with the solar panel sitting beside the car!

If you were to mount the panel on the roof of the vehicle you don't need to worry about it blowing up. The mains-powered charger will get confused about the level of the battery and might consider it full and simply stop supplying power. The regulator on the solar panel might do the same thing - at worst, you'll have a battery that isn't fully charged, but the chargers won't damage each other.

If you're really worried about it, you can isolate the two by using a relay. If the vehicle power is on, it throws a relay that disconnects the solar panel from the system. As soon as the vehicle is turned off, the relay flicks over disconnecting the car and reconnecting the solar panel. Since the two will never be connected together to the battery at the same time, you'll never have an issue with the battery not being fully charged. Only problem here is that you need a relay that can carry the amps being delivered by both.
 
Old.Tony said:
If the battery's a permanent installation then it should be charged by the car while you're driving around.

Once you're camped the car isn't running, so the solar panel won't be competing with anything.

If you hook both up directly to the battery I can't see any issue. You can't drive off with the solar panel sitting beside the car!

If you were to mount the panel on the roof of the vehicle you don't need to worry about it blowing up. The mains-powered charger will get confused about the level of the battery and might consider it full and simply stop supplying power. The regulator on the solar panel might do the same thing - at worst, you'll have a battery that isn't fully charged, but the chargers won't damage each other.

If you're really worried about it, you can isolate the two by using a relay. If the vehicle power is on, it throws a relay that disconnects the solar panel from the system. As soon as the vehicle is turned off, the relay flicks over disconnecting the car and reconnecting the solar panel. Since the two will never be connected together to the battery at the same time, you'll never have an issue with the battery not being fully charged. Only problem here is that you need a relay that can carry the amps being delivered by both.
Click to expand...

Hey Tony, I was hoping you would see this :p
I will just buy a cheap solar charge controller then and hook it up to the battery when the car is stopped. At this stage I wont run the solar connected permanently but i will keep the relay idea in mind for the future.
The panel is a Solarex SX60u.
SX60U-specs.gif

What sort of controller would I need? But on the other hand i don't want it failing to charge the 100ah AGM properly.
Am I right in saying I just need one rated above 3.56 amps?
Cheers
Martin
 
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Personally I'd get something over 5A - Jaycar have this one which is reasonable and takes 6A, costing just $49.95. The one I'm using is this one from Jaycar as well, it's a 20A controller - but I have an 80W and a 64W panel on the roof of our van - will be changing that 64W panel to an 80W soon.

The 6A controller delivers 14.3V which is a little low for an AGM but it won't kill the battery.

My 64W panel could provide 4.5A in bright sunlight, but that wasn't enough to provide enough energy for everything we ran in the van. The fridge (140L Waeco) draws about 5.5 to 6.5A (say 6A) when cycling which it will do about 50% of the time, so overnight (say 7pm to 7am or 12 hours) it uses 6hrs * 6A or 36 amp hours (Ah).

During peak sunlight time (10am to 4pm = 6 hours) I need to replace that - which means I need to have an excess of 6A over and above anything being used at the time. In the shoulder periods, I find that we pretty much break even - there's enough light to just keep the battery about constant. The 4.5A during peak time would only give 27Ah but the fridge would draw 6hrs * 6A / 2 = 18Ah so the net gain was only 9Ah, and I needed 36.

Generators are bloody handy!

If you intend to add more panels later, go the larger regulator now so that you aren't throwing money away later.
 
Personally I'd get something over 5A - Jaycar have this one which is reasonable and takes 6A, costing just $49.95. The one I'm using is this one from Jaycar as well, it's a 20A controller - but I have an 80W and a 64W panel on the roof of our van - will be changing that 64W panel to an 80W soon.

The 6A controller delivers 14.3V which is a little low for an AGM but it won't kill the battery.

My 64W panel could provide 4.5A in bright sunlight, but that wasn't enough to provide enough energy for everything we ran in the van. The fridge (140L Waeco) draws about 5.5 to 6.5A (say 6A) when cycling which it will do about 50% of the time, so overnight (say 7pm to 7am or 12 hours) it uses 6hrs * 6A or 36 amp hours (Ah).

During peak sunlight time (10am to 4pm = 6 hours) I need to replace that - which means I need to have an excess of 6A over and above anything being used at the time. In the shoulder periods, I find that we pretty much break even - there's enough light to just keep the battery about constant. The 4.5A during peak time would only give 27Ah but the fridge would draw 6hrs * 6A / 2 = 18Ah so the net gain was only 9Ah, and I needed 36.

Generators are bloody handy!

If you intend to add more panels later, go the larger regulator now so that you aren't throwing money away later.
 
Yes.

The more expensive controller is factory configured for GEL batteries, so it will deliver 14.3V just like the other controller. With the flick of a microswitch in the side, it will charge at 14.8v, which is good for AGMs and wet (normal) batteries. You can modify this so that it's anywhere from 12.0V to 16.5V, but I don't recommend exceeding 15V on deep cycle, AGM, starter or any other "normal" kind of battery. 15V on a gel battery will kill it over time as the gel hardens and cooks.
 
Don't apologise for the questions. There could be any number of other people out there wondering the same thing too, so it's all helpful.

If you're not going to get more panels and you're happy to have the battery slightly undercharged (you can top it up when you get home) then the cheaper unit is fine, save yourself some $ and go for it. You might take a look at some other suppliers like the 12 Volt Shop , the Home Of 12 Volt, or an alternative The 12Volt Shop.

I'll do some of that legwork for you - the first and last ones only have more expensive stuff but it's not bad if you were after something more heavy duty, and the Home Of 12Volt has the same controller that Jaycar sells.

Undercharging the battery won't kill the battery, but unless you give it a top-up to full power once you return home, you will eventually kill the battery through sulphation. I don't think AGMs suffer from this as much as other battery types, so doing a charge once you're home and using the cheaper controller while you're out is not a bad solution.
 
As the Redarc SBI SmartStart only charges to about 75% of battery's capacity, will the solar panel (and the cheap controller) take it almost to full once I have stopped the car?

I was just looking at the enlarged picture of the cheaper controller and it has the PV terminals, the battery terminals and then the load terminals. Do I just hook up the panel to the PV terminals and the battery to the battery terminals an not worry about the rest? All the load is coming off the battery directly.

Would the load be all the accessories or would it be an input for a generator for night time charging etc?
 
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The solar panel won't get the battery to full charge either, because the cheap controller will limit the power to 14.3V - which is for Gel batteries, not AGMs which need 14.7-14.8V to fully charge them. You'll get the battery to about 75% capacity, perhaps 80%, with solar.

Set up as per your second paragraph is the way to do it. The load terminals are for a light load anyway. You don't need to use it, and in our caravan we don't use the load terminals or the nightlight function. We have the solar panel input and the battery output and then let the battery handle the power going off to devices directly.

If you want to hook up a generator, do so, but don't use the 12V output of the generator, because that's designed to BE at the 12V level so you can run 12V devices with it, which means it's not enough voltage to charge a battery. To use a generator effectively, plug a 240V charger into the mains outlet of the generator and charge the battery directly with that.
 
The back-current is negligible so it's safe to leave it connected, and the regulator might even disconnect the panel unless the incoming voltage is over a certain limit, preventing that back-current.

The problem with leaving them out overnight is not so much the back-current or potential for drain, it's the potential for some ass to score a nice solar panel and disappear while you sleep.
 
Hi again,
I am also looking at purchasing a Projecta PC1600 to charge my 100ah AGM off of 240v. But if I wanted to run it in the car off an inverter (similar to your setup Tony), what inverter would I need? I know nothing about inverters so am flying blind at the moment.
Cheers
 
I'm not sure I'd pump 16A into an AGM to charge it, that 8A PC800 might be a little kinder to the battery. Charge 'em up too fast and they cook. If you can select 8A as the usual charge max then it's a good call.

The specs page says it will require 432Watts to run, round that up to give yourself a little room - say 450W - that's nasty, it's a 37 amp load. It will require some very heavy cables run from the car through to the van, at least 8 square mm stuff and a proper Anderson 50A plug separate to the trailer plug.

The PC1600 would require a 600W inverter (so it'll last), Jaycar have a good 600/1500W unit for $169.00. Don't forget to add a bunch of higher spec cable for this guy, and a decent fuse up front.

If you go the PC800, it requires 240W to run, that's a 20A load and you can use 6 sq mm cable and run that through a normal 12-pin trailer plug.

If you're managing your battery well, you're only using 50% of its full capacity (50A) and 50/8A charge rate = 6.5 hours to recharge.

An inverter that can drive this is the 300W/1000W unit from Jaycar (this is the one that I use) and costs $69.95.

Hope I've helped!
 
Just to add my reasoning for using an 8A charger rather than a 16A: most wet batteries prefer to be charged at C/10 (capacity divided by 10) Amps. Any higher and the plates start to degrade and buckle and the charge across those plates will cause enough fizzing that it may overpressurise the battery and cause hydrogen gas to escape, with the obvious detonation risk.

The 100Ah battery should be restricted to a max 10A charge rate.
 
Hey mate,
Yeah the PC1600 has an 8amp setting I am pretty sure so I will run it on that setting (or closest to it).
Will the 600W inverter draw to much power from the main battery for the alternator to keep it charged to a reasonable capacity?
 
It will draw about 50A. Your alternator will not deliver that much at idle, you'll have to keep the revs up over about (at a guess) 1500 to maintain charge.

It's a lot of power to send down a long cable, too. You'd need a 50A fuse up near the battery (I forgot to mention that earlier). Probably best to run that through a relay that's activated by the ignition too, make sure the relay can handle over 50A.

If you're only drawing 8A your inverter won't have to work as hard. You'll find that at 8A, the charger won't charge the battery too quickly and draws a small enough amount of power to use more reasonable wiring and connectors.

The inverters will only draw as much power as they need, so plugging in the charger and charging at 8A should need about 240W (per the PC800 specs) or 20A.

When I think about it, that's a big, big power loss - that charger seems quite inefficient.

I would expect an 8A charger to use no more than 150W. That's 15V (max voltage) times 10A (8A for the battery, 2A for the on-board circuitry).
 
i got a cheap controller off ebay for a couple bucks it charges at around 22v i only tested it out didnt leave it on sounded a bit high for my liking. should i throw the controller and get another
 

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