Need a multivoltage charge controler ??

[Tobym]

Hi I've been looking for a cc that I can charge my batteries at 24v but get 12v on the supply side. Does this exist or should I use a step down transformer 24v>12v and will this be less efficiant than just charging the batteries at 12v even tho my panels are higher voltage panels so amperage would be lower. Thanks toby

[kibi]

Hello Toby.

A higher voltage battery bank is more efficient because with a 24V system you have half the charge current that a 12V system would have. You cables do not need to be so thick.
If you do not have a charge controller at all yet then I'd suggest a good MPPT charge controller. Look for Morningstar, Outback, Midnite or Victron MPPT charge controllers for a start, these are all good brands. Do try and avoid the Chinese ones, some of them even say that they are MPPT when they are not.
The advantage of an MPPT charge controller is that it can charge any common battery system voltage (12V, 24V or 48V) with any solar array voltage as long as the array voltage is higher than the battery voltage. MPPT charge controllers usually support 150V arrays and are able to charge 12V systems with no problems. The less expensive PWM controllers need to have the solar array voltage closely matched to the battery voltage because they waste a lot of energy if the solar array voltage is much higher than the battery voltage.
So, if you went for a MPPT charge controller, you could have a 12V battery bank which would solve your 12V supply problem.

If you decide to stick with a 24V battery bank either with a MPPT charge controller or a PWM charge controller with a suitable solar array voltage then you'll need to have a DC-DC converter. These are common in the market. Lorry drivers use them to get a 12V supply from the 24V electrical system of the lorry.
Victron do some good ones:

http://www.victronenergy.com/upload/documents/Datasheet%20-%20Orion%20DC%20DC%20converters%20-%20rev%2013%20-%20EN.pdf

I hope this helps.

[kibi]

Toby.

Please ignore my above post. I have provided a better answer based on more information in this thread: http://mjlorton.com/forum/index.php?topic=305.0

[Tobym]

Toby.

Please ignore my above post. I have provided a better answer based on more information in this thread: http://mjlorton.com/forum/index.php?topic=305.0

Hi thanks for that the tread you supplied just brings me back to here. I have decided to stick with a 12v bank and use a 60a mppt cc. I currently already have a 12v 145ah truck batter so I'm gonna use that instead letting it go to waste and at a later date wen this battery needs replacing ill sort a larger bank. What I would like to know is that if I want to add another 12v battery but keep it it at 12v I would need to run in parallel which I have been told is a big no no so would the only way to do this be to split the panels and use two charge controllers and then have two separate loads thanks again Toby

[kibi]

OK, so the truck battery will keep you going for a short while. Don't expect it to last vey long since it is not designed for deep discharges. It's good to get some use out of it and it will give you a better chance to work out what size deep cycle battery to buy and hopefully give you enough time to save up for a good bank.
Now, what you have been told about batteries in parallel is correct, up to a certain point. Ideally, you shouldn't run batteries in parallel at all due to current sharing between the strings. However, this is not always practical especially on 12V systems such as ours where you need high amp hours because of the lower voltage.
DO NOT connect another 12V battery in parallel with your old truck battery. One of the two batteries will undercharge and the other will overcharge.
NEVER connect dissimilar batteries in parallel.
DO NOT connect batteries of different amp hour ratings in parallel ( or series for that matter).
YOU CAN connect two of the same batteries, bought at the same time in parallel.
DO limit the number of parallel strings of batteries. Two strings should give you no problems at all. You can have up to four, but this is just increasing your chances of one string going out of balance.
I have two strings in parallel to get the Ah rating up.
Get the best batteries that you can afford, buy the whole bank at once. You will not be able to add more batteries in parallel once you have used your current bank for any length of time even if your current bank is still strong.
Aim for as shallow a dischage as possible to increase the life of your bank. So, for example, if you use an average of 100Ah in a day, aim for a 1000Ah bank to keep your bank from being discharged below 90% on average.
I'd highly recommend using a good battery monitor. Keeping an eye on the voltage is simply not enough. The Victron BMV-600 is really good. I have seen the older BMV-500's going a bit cheaper, still a good unit.
There are many choices with regard to batteries. Go for flooded ones if you can keep them warm and ventilated. I went for AGM because of ventilation issues. Flooded batteries kept in poorly ventilated areas will cause explosion risks and will cause corrosive gasses to fill the air. Flooded batteries do require regular maintainance, but if looked after well will provide many years of good service, longer than AGM or GEL types.
Let us know what you are planning for battery wise, and I'll be happy to advise.

[Tobym]

Ok cool so battery wise I have a conection at my local scrap merchant who had the contract with a firm that maintains the back up electicity for banks and such like they deal with the generators and on top of that these battery back up systems which are huge apparently up to 5 ton of batteries at a time. Now these batteries are deep cycle batteries that are sat charging on an optimising system with only a test real life load  on them once a month by the engineers as part of the contract they are all replaced every 5 years. Now I know what u are going to say that they are potentially at the end of there life but he often sells them solar blokes as he calls them. Now he is going to sell them to me at 50 pence per kg above scrap weight so as long as I check them even if they only last a year which I can't see y they would not last a few then buy the time I scrap them back in and buy more they have only cost me a few £. He gets in a lot of 12v100ah and 75ah he also gets a lot of 6v I think they were also 100ah so was planning on getting 4 -6 of the 6v and doing 2-3 strings of 2 in parallel. Does that sound dooable thanks Toby

[kibi]

Now I know what u are going to say that they are potentially at the end of there life.

Not quite. I'd say that those batteries are in very reasonable condition given their previous application. They have most likely been well maintained and been on a float charge most of the time. True, I wouldn't want to pay a lot of money for them, but if you can get them for the price that you can then you'd mad not to use them.
The reasons I gave before about getting the biggest and best batteries that you can afford are based on full price, new batteries. When spending large amounts of money one want's to maximise their investment.

The cost of your batteries now means that we are playing a different game.
I'd usually say that a 300Ah bank would be a bit small based on rough estimations of your consumption. Based on a 100- 150Ah daily discharge cycle (my be less), a 300Ah bank will supply you with enough energy for the day, but the discharge cycles will be deep (50% or so). Regular discharge cycles this deep will shorten the service life of your bank, but if you can replace your bank cheaply then you don't really have a problem.

So, go for six 6V batteries, two in series and then three of those in parallel. Be sure to wire them up correctly, see the illustration below. This ensures that the current is shared equally between the parallel connections.



Congratulations, those batteries are a really nice find.

Have you decided what charge controller to go for?

[SeanB]

What I did with paralleling batteries was to make the end connections all the same length, and having a star point for each end. added bonus was being able to disconnect any bank to check it if needed without needing to power off.

[Tobym]

Thanks very much gentle men I've been looking at the charge controllers. Dang they expensive it looks like I'm not gonna get away with less than £300-£500  for any thing half decent even the the Chinese ones aren't cheap lol. Odly enough I can't seem to find a lot of option on 60a does any one know anything about these http://www.ebay.co.uk/itm/221080020594?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2648 thanks

[Tobym]

I e just looked at the mine from bimble that kibi sowed me and its the same one 

[kibi]

I have seen those ones floating about on eBay. Bimble Inn sell it, so people must be using them and if it was rubbish people would be complaining.
I personally don't know very much about it, so I can't tell you if it good or bad. If it does what it says it does then it will be perfect for your system. The price is very reasonable.
One thing to be aware of with this charge controller though is that the PV input voltage needs to be above 40V. You will therefore need to wire up your panels 2 in series and then the 2 series strings in parallel to ensure that the PV voltage remains above 40V.

[Tobym]

Ok think I may just go for that one then and c how it goes ill make sure I let every one know how it goes thanks so much again for your help. Nice to go on a forum that's not full of people who know "everything " and treat you like a moron because u don't.

[kibi]

No problem at all Toby. Please do let us know how you get on, I always find it interesting seeing other peoples projects and learning from their experiences.

It's a pity when other people treat newbies badly. When I was born, I knew nothong. When I die I will not have known everything. We all have to learn from each other. Sometimes it's your time to teach, other times it's your time to learn. Simple

[Tobym]

Hi again so I went to order the above mentioned cc and asked a few questions and found out its a very simple device which has no battery/load monitoring abilities at all as its apparently was originally built as a simple battery charging unit and the just added the load terminals at a later date so they are just an open link to the battery terminals. So there is no lvd or hvd on the unit and as it needs 40v to make it work as soon as it gets below this it stops charging the batts. I wanted more monitoring and controll and I haven't been able to find any other cc's that fit the bill. So is there any reason why I can't split the panels and run 2  30a cc's and then charge the same bank of batts from both systems  http://www.ebay.co.uk/itm/271187511417?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2648. These look perfect has anyone got any advice thanks Toby

[kibi]

Hello Toby.
It's a pity that didn't work out. It's a good thing that you asked the questions though.
There is nothing wrong with splitting your array up and using multiple charge controllers. This is the only way possible if you have a 40KW array on top of your safari hotel for example.
Again, I don't know too much about that charge controller, although it doesn't appear to have monitoring or logging, but not too surprising at the price.
If you want it quicker than four weeks, it is available locally for a bit more money from here:
http://www.swithenbanks.co.uk/Solar_Photovoltaic_Equipment/1130303/Provista_30A_MPPT_Solar_PV_Charge_Controller.html