thanks for that kingcab. thanks heaps old tony, really really helpful info. sorry im quite new to this whole battery talk. but having heard what you have to say on dual battery setups and how inefficient charging off the alternator alone is, i cant help but think i have just wasted a whole bunch of money on a new db180s pirahna system, when maybe i should have just got the ctek charger and an inverter for probably the same cost. is this the case or would the c-tek charger just be a good addition that would work in well with the pirahna system? :/
Power inverters?
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I don't know how the pirahna system works, I never bothered with off-the-shelf solutions because they all (example: Redarc) work off car battery voltage. Don't get me wrong, they do have their uses - they will stop your secondary system from draining the primary battery and when you're "out there" with little help at close hand, that's vital.
Something tells me the Pirahna system may let you reverse the power - either use your auxiliary to charge up your main battery, or to even start the vehicle off the aux battery. That's something the inverter/charger system won't allow.
If you don't need to be able to start off the aux battery, the ideal connection is like this:
Mainbattery -> fuse -> relay -> cable -> inverter -> charger -> auxbattery
But the system you bought will at least protect your main battery. Count on about 20-25% of your aux battery's "RC" figure as usable capacity. If your AUX has an "RC" of 70, then you could reliably count on using 14Ah-17Ah (that's 14 to 17 hours with a MT60 Engel chest fridge, in mild weather). If you're touring and only stopping for the nights, that's more than enough.
Would a C-Tek charger be a good investment AS WELL? Absolutely. At worst case, you can use it to recover a partially sulphated battery. Just be aware that they aren't $50 jobs from Supercheap - my 7A XS7000 cost me $300 or so.
Something tells me the Pirahna system may let you reverse the power - either use your auxiliary to charge up your main battery, or to even start the vehicle off the aux battery. That's something the inverter/charger system won't allow.
If you don't need to be able to start off the aux battery, the ideal connection is like this:
Mainbattery -> fuse -> relay -> cable -> inverter -> charger -> auxbattery
But the system you bought will at least protect your main battery. Count on about 20-25% of your aux battery's "RC" figure as usable capacity. If your AUX has an "RC" of 70, then you could reliably count on using 14Ah-17Ah (that's 14 to 17 hours with a MT60 Engel chest fridge, in mild weather). If you're touring and only stopping for the nights, that's more than enough.
Would a C-Tek charger be a good investment AS WELL? Absolutely. At worst case, you can use it to recover a partially sulphated battery. Just be aware that they aren't $50 jobs from Supercheap - my 7A XS7000 cost me $300 or so.
merchant
Member
Old.Tony, what battery monitor do you have in your van? I have just installed an analogue volt and amp meter in the boot with all the rest of the electrics and am now considering installing a NASA Marine BM-1 compact monitor inside the van.
There's no brand on it. I think it was purchased about 11 years ago from The 12V Shop in WA as part of the "ATK Battery Management System". Parts of it look like it's been made from kit boxes and for mains battery charging I've bypassed it so that the C-Tek charger can manage the battery itself.
Old Tony - I am looking to do this exact setup, after your advice. It seems to make perfect sence. I have a few questions though which I hope you can help me with;
1. Why not just use a C-Tek DC to DC charger and do away with the inverter? These are super smart chargers (at a high $ price)
2. What is the relay in the line between starter battery and inverter for? I'm assuming this is a failsafe to ensure the inverted doesn't keep running when the ignition is off, but my inverter cuts out when the supply battery reaches 10V. Is 10V an already 'too low' point?
3. What rating is the relay? Something I can pick up from Jaycar or the like?
4. What size cabling have you ran from starter battery to the inverter - is this a big deal?
5. To bring your aux battery from 50% charge to 100% charge, how long does it take just running form the car/inverter?
Thanks heaps Tony,
Tim
Because they don't fulfill all of the task required. I require that the fridge auto-switch over to 240V while that's available (which it does) so that the battery is unloaded and the charger can properly sense the state of the battery's charge. To do it any other way risks the charger not knowing the actual state of charge of the battery and thus charging it incorrectly. The reason is because when you place a load on a battery, the voltage drops, and the only means the charger has of determining the state-of-charge is to look at the voltage.
I also like having the 240V there in case I need to charge my cordless drill or other widgets.
The relay is to ensure that the power to the rear of the vehicle is only available when the ignition is on. This way, the alternator is able to supply charge current and your starter battery is protected.
And 10V - absolutely it's too low. Below 10.5V is where lasting damage occurs to starter batteries. If you try to start your engine when the battery is below this level, you're not only encouraging sulfation but warping/collapse of the plates within the battery.
I never allow a battery to fall below 11V and that's worst-case.
It's a standard automotive 40A relay. It only has to carry the current you're likely to draw down the cable and I would recommend at least a bit more than the size of the fuse you put in line (I have a 30A fuse). This is because even though the fuse is 30A, it won't blow at 30A of current, it actually needs more. Give yourself some margin for error.
The cable I use is 60A cable, 6sq mm in of conductor. This isn't to carry the current - which we expect will be about 10A (6A charger, 2A fridge, 2A for losses) - it's to maintain voltage over distance and prevent the cable from heating up and catching fire.
I've only got a 50Ah in the back, so it takes about 4 hours to charge it up with the 6A charger I've got in there. Since (when we're touring) we drive for a lot longer than that, we obviously have a fully charged battery when we arrive at places!
The other advantage in doing it with individual components is flexibility. If my charger dies, I can whack a cheapy on as an emergency measure so that it at least mostly charges the battery up. If the inverter dies, I can get them at a reasonable price from all over the place.
Hope that helps!
terryc
Member
About 5.5hours.
The recommendation for long useable battery life(lead acid deep discharge) is C/10 maximum discharge/charge, where C=Capacity.
Thanks Terry - but i'm a bit slow with this stuff, what does that mean for a AGM deep cycle 100ah battery - can I only safely discharge as low as 50% before having to recharge? (as suggested by Tony) Or can I go lower?
K
KraftyPg
Guest
Of course you can go lower, how much and how often is the bit where opinions become divided.
Certainly does Tony - great information. Thankyou very much!
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Terry's making a good point that I'd overlooked with my own setup.
The "C/10" rule basically means your maximum charge rate for a deep cycle battery should be its capacity divided by 10. In the case of my 50Ah, the max charge rate should be 5A and therefore should take 5 hours to charge it from 50% (or 25Ah).
I am doing damage to the battery by charging it at a higher rate. Good call Terry, I'll go looking to see if I have a 4A charger in the shed.
As for the maximum amount of discharge - you'll probably find that your fridge will dictate that. Once the voltage drops to a certain level, the compressor won't kick over any more at which point there's no purpose in continuing to run it.
As a general rule, you'd use no more than 50% of the battery's capacity (terminal voltage around 12.2V unloaded). That said, some battery manufacturers will say that you can use up to 80% of the battery's capacity - the Gel in my caravan (Century Battery, 100Ah) tells me precisely this.
I still only use about 50%, just to be on the safe side.
terryc
Member
Jaycar sell some battery cutoff blocks that you can wire in to save your battery. No idea how good yet. I purchase three recently, but the delivery of the CT is dragging out to over a month, so I haven't had a chance to measure and order the bits; fridge(s), solar panels, batteries, etc to install and see how good.
terryc
Member
I have no idea. I've always stuck to deep discharge lead acid batteries.
It is my understanding that batteries like AGMs are more restricted in their charging/discharging regime. Hint, if someone tells you otherwise, ask them what life they are getting from their AGMs. Some people think three years is fine. I prefer to aim for ten years for my DDLAs, hence the gentler treatment.
Generally, the shallower and the gentler the better.
If you are considering fridges(comparative heavy draw), then you need to consider usage and maybe change behaviour. Also, I seem to remember that some fridges drag a constant Xamps on 12V(no thermostat), but less on 240V(thermostat works).
As to size, your maximum size is determined by how much you can lift and fit. My lot weight 35Kg each for 125AmpHr. You could put two IDENTICAL batteries in parallel for more capacity, but for my next lot I'm going 2x6V 225AH in series. Well, that is the theory anyway.
BTW, I've found that the cheapest place to buy is places that service forklifts, etc and not places like SCA, Repco, AB or BW.
You'll commonly see this in 3-way fridges.
3-way fridges are grossly inefficient on electricity. If you have to use one, just use it in gas mode and forget the electric side of it, it's a waste.
In 12V mode it'll draw 10-12A solid. In 240V mode it's rated at 10A which is 2400W - before I replaced mine, I had never tried running it in 240V mode on the generator.
sorry to dig up an old thread but i just wanted to know if anyone can give me a heads up of the differences between a normal inverter and a pure sine wave inverter and what type of appliances as an example that wont work on a normal inverter.
thanks
kyle
thanks
kyle
Cooper
Member
I use deep cycle batteries in both slots. Get them cheap so why not. For your aux battery you should always use deep cycle. It's not rocket science why to either. Wire in a cheap volt meter and soleniod to disconnect below 11v so you won't harm your electronics. If touring for ages outback camped in one spot get a 3 way fridge. Mine lasts 27 days on a small bottle of gas with constant use. Make everything convenient and you won't have any troubles. The kiss method is fantastic?! Onlock you want a pure wave for things that do not have a transformer either built into the electronics circuit or added to via power adaptor due to a square wave inverter has a magnetic field that rises and collapses very quickly which you could say is not a very delicate way of delivering voltage to a sensitive electronic equipment. Pure sine wave inverters generate supply voltage that slowly rises up and slowly collapses giving basically constant smooth voltage for your electronics. Now if your equipment has got a step down transformer to 12v the transformer also helps to smooth out a square wave using magnetic fluxes ect... Basically if you like your delicate electronics and wish to not worry if it has a transformer built and to use for years to come use a pure sine wave. Or if what your going to use it for ain't that important get a square wave. It's basically put down to this.... You like slow rising swell and waves I'n your boat or arse jarring back hurting windy chop for the rest of your working life? Sorry grammar and shit is bad using my phone.
Cooper
Member
Also spend the bucks upfront on deep cycle maintenance free batteries. They make them so good now that the best really are a cut above. They automatically disconnect the supply to avoid plate warping ect when too low hence maintenance free. They are what start your car and you need them reliable in the bush or winching ect no point having to ask bear grylls to tell you your proper farked when theyre flat and won't get you to your nearest town if you stall after a jump start hahahahha. Seen it happen. Proper farked!
terryc
Member
No problems.
AFAIK, square wave inverters are the dinosaur version.
Most inverters are modified sine wave inverters, i.e. the sin wave is approximated by a series of steps, the more the better.
Also, a lot of stuff uses inverter PS these days, even some little plug-packs. are not as fussy.
The devil is in the detail, so better guidance on exactly what you are trying to run would give better info, e.g. air-con or heavy motor, then get a generator.
Otherwise, a good brand of MSW inverter will run most stuff.
Lap tops with external PS are usually fine, but run hotter. Worst case is you buy a new cheap external PS(would perform better anyway). I have actually smoked a 60watt inverter running a laptop that said 60w max. No problems with ancient toshiba laptop.
What you most definitely can not run safely is equipment with power switching that relies on the Zero crossing in the sin wave. MosFet(?) circuitry. These things are not designed to switch large currents, but to switch the instant the voltage changes polarity in the AC. They tend to fail if asked to switch large currents.
The only common example I know is CPAP machines. Most can run fine on MSW inverters, provided they do not have the heated humidifer attached. It is the switching circuitry in the humidifers that is the dangerous bit.
Unfortunately, if equipment manufacturers can see an opportunity to sell you more gear they do not provide information on use with an inverter. Also, some love pointing to an inverter to avoid a warranty.
You are best to state what gear you are looking at running on it and see if someone has experience.
FWIW, I've run stuff on a Jaycar 300w for over a 15 years and apart from a broken 240V socket, it has been fine.
+1 for everything Terry said.
Don't EVER be fooled by companies advertising "pure sine wave" inverters, either. In digital technology, it can only be approximated by a computerised switching device.
In my experience, the Jaycar modified sine wave inverters are more than adequate, and if you're worried about things like your laptop, you can purchase a DC-DC converter like this one that I use:
which is more efficient than inverting the power and then using a step-down transformer again. Every time you change the voltage, you lose a little power in the process, and when you're away from it all, it's important to not let that happen too much!
Don't EVER be fooled by companies advertising "pure sine wave" inverters, either. In digital technology, it can only be approximated by a computerised switching device.
In my experience, the Jaycar modified sine wave inverters are more than adequate, and if you're worried about things like your laptop, you can purchase a DC-DC converter like this one that I use:
which is more efficient than inverting the power and then using a step-down transformer again. Every time you change the voltage, you lose a little power in the process, and when you're away from it all, it's important to not let that happen too much!
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