24v to 12v

alright71

I am considering purchasing some 12v LED lighting for my house. The problem i am encountering is that my batteries are 24v. I have found both equalizers and DC to DC converters to take care of this issue. My difficulty is in deciding which one to use. I plan to have no more than 10 to 15A of total load (other 12v things besides just lighting).

Which method (equalizing or direct conversion) would you prefer for your own system?

BB.

Re: 24v to 12v

I am not sure I really "like" either option...

My choice would be to buy a small/efficient 24 volt to AC tsw inverter and use 120 VAC (or 230 VAC) LED/CFL lighting. The cost of a equalizer or 24 volt to 12 volt converter is about the same as an AC inverter (sometimes the inverter may be less). And sending DC power any distances can require heavier wire to keep the voltage drops load (i.e., 10 amps at 24 volts with 0.5 volt vs 1 amps at 240 VAC and 5 volt allowable drop).

If your wife is in the US at the moment---Another option would be to look for Boating (or even trucking) 24 volt light fixtures.

Here are a couple examples of 24 LED (don't know anything about products or websites):

http://www.led-cfl-lighthouse.com/page/1433707
http://www.sailorsams.com/24-volt-led-lights

Note that the threaded DC lights may not match what you get locally in Africa.

In the US, you can purchase 120 VAC LED lights cheaper than the 24 volt DC versions.

-Bill

Cariboocoot

Re: 24v to 12v

One of the usual problems with low Voltage lighting is the Voltage drop over distance necessitating large wire to keep the lights bright. With LED's the current is very small, so this may not be so much of a problem.

Another option is to wire two 12 Volt lights in series. But they have to be matched and the LED's lights may not 'behave' if connected in this manner as one will affect the other.

Bill mentions using a small 24 VDC inverter like this Samlex http://www.solar-electric.com/sa300wa24vos.html and running 120 VAC for lighting. On the whole that is much simpler.

My personal take is to reserve 12 VDC systems and equipment for applications where it is necessary, i.e. RV/mobile applications where everything else is 12 Volt.

alright71

Re: 24v to 12v

I understand exactly what you are saying about ease of use and the difficulties with lower voltages and long distances. I have several motivating factors for my question, and for wishing to use this method in my house. But first, let me provide you with a tinny bit of history.

In the past, missionaries brought EVERYTHING from home. This was for several reason...primarily, it was what was familiar, lower cost and higher quality. By bringing most everything from the US, missionaries were able to do things which during that time, were not possible, for example...bringing a generator to have power. Another example would be to ship beds from the US because what the nationals would sleep on is little more than a grass mat on the ground. I think you get the picture.

The problem which arose from this is that any replacement parts must come from wherever the item was purchased from. Yamaha US or Yamaha EU is totally different stuff than what is available at the Yamaha dealership in Kinshasa. A Yamaha generator from the US will require parts from Yamaha US. I think you can see the huge problem this creates.

All CFL light bulbs here are 220v...a 110v inverter will do me no good unless i also want to ship light bulbs in from the US.

In present times, Africa has been opened up to a much wider variety of items in varying degrees of quality. You can purchase 6KVA generators from India for $2000. You can purchase Chinese everything also in varying degrees of quality. The problem now is to distinguish between the cheep junk and the good stuff.

A debate has now emerged between shipping the good "original" things from home that you know and are familiar with, or trying to make due with what is available on the local (or close to local) market.

I am in the process of renovating a colonial era warehouse in which national Bible translators will do their work. When complete, this renovated warehouse will house over 60 translation and literacy projects, more than 200 laptops, servers, a full print shop, a 200 person conference hall, 2-15 person board rooms, a mechanics shop, and a 12 bed guest house. All of this is being done in a town with 0 electricity service.

From the above description I think it is quite simple to say that I have a HUGE task at hand. Now it won't all be done at the same time, it's expected to take 3 years to complete the renovation and after that the numbers of people and equipment will ramp up over the next 10 years. But never the less, its a lot of work!

So now...keeping this project in mind, and thinking about the argument of cheep and locallyish available or high quality, expensive and shipped across the ocean at a cost of $10,000 per container (shipping from Galveston port to Gemena). You can see that i have a huge decision to make! My power budget for this project is going to be outrageous!

I am trying to use my home as a small scale proving ground for whatever technologies will be used in this renovation project. These 12v tube lights are locally available and should provide enough light for the translators to do there work...but i need to test it out. My cheep VRLA batteries should give me around 3+ years of service, but i need to test them out. I have 6 cheep, 120w 12v panels...i need to test them out. I am trying to use all locally available stuff, so that when something breaks, it can be repaired in 1 week instead of 1 to 2 months.

Now for my project, i plan to build a 12v secondary PV system to power the lighting, but as a temporary measure i need to create 12v for my house, as efficiently as possible.

Does that make sense? With all of this additional information, do you still feel i'm still looking in the wrong direction?

I really appreciate everyone being so willing to help me get this sorted out with the best information available!

Blake

Cariboocoot

Re: 24v to 12v

Doing a little research on South Africa's "power standard" and it appears they haven't got one.
It seems to be headed for the EU standard of 230 VAC 50 Hz, utilizing old British plugs, with some areas using 220 and a couple at 250. For the most part it appears EU standard will work.

So you should set your sights on that. This means it will be possible to import from EU countries and/or use what is available locally. As long as the Voltage (+/- 10%) and frequency match it should all work together.

In my opinion buying the cheap stuff from India or China is throwing money away. I've heard that some of the "Lister" generators from India need rebuilding before use because they never clean the casting sand out before assembly!

Looks like you will be learning on your home project so as to get the warehouse project right. Normally we don't recommend trying to expand a system, but in the case of the warehouse project you have an opportunity to install "one work station's worth" at a time, keeping each entirely independent and redundant. If one power section does fail its equipment may be run off another section. How much division should be done will depend on the final # of workstations and their power requirements.

Most solid-state devices such as inverters or charge controllers are not going to require repair. If they do it is usually impractical even on these shores; replacing would be cheaper. As such trusting in buying good equipment like Outback (famous for their durability and available in EU output standard) would be worth the extra $: "Buy it once, or buy it repeatedly" so to speak.

Whenever you do a large-scale design such as a whole house it is much more practical to keep as much of the wiring as possible on the local AC standard so that you only have to deal with DC on a small scale: powering the inverter(s) and charging the batteries. Having a mix of supply for devices after that can present problems.

Just so you know what you're getting in to, some OB 230 VAC 50 Hz inverter-chargers: http://www.solar-electric.com/oupoinoffgrb.html

BB.

Re: 24v to 12v

Blake--Understand completely and agree... Very similar to a design engineer--You want Cheap/Fast/Reliable... Pick any two.

I agree with trying to source everything locally. And sometimes compromises need to be made.

Regarding LEDs--Bulbs with the rectangular/square LED "chips" and lots of heat sinking (heavy bulb with aluminum fins, etc.) are usually better than those "old fashion" Txx type plastic LEDs with leads... The leaded LEDs tend to overheat and "cook" the plastic and phosphors (not enough metal to remove heat, mfg. "push" more current to get acceptable brightness). Many LED's with 10-50,000+ Hour ratings will fail in the first 100-500 hours of use.

So, highly recommend that you put the items on a test bench setup to see if they perform as expected and will last.

For example, DC solar power battery banks have a wide range of "working" voltages--From ~21.0 to 32 volts at the extremes. You will find that many "24" volt devices will only work "well" from 24 to 29 volts, and if operated out of those ranges, the appliances/converters will either not work or can even fail.

That is another reason I like using inverters to convert to 120/230/240 VAC... All of those "problems" with DC voltages affect the inverter only--Not the 20 different DC adapters/appliances you have around the place.

Especially in the US/North America, but probably leaking out to the rest of the world now (via China, et. al.), are the very energy efficient AC appliances now. Many of the "good ones" (such as energy star rated refrigerators in the US) are almost as efficient as their "off grid" DC counterparts. At 1/4 the price or less and last 2-4x longer.

I would suggest that in addition to anything else you get from the US, to purchase some tools. Hydrometer, Battery Monitor, etc. will help you monitor your battery bank (and learn). And some other tools like a couple Doc Wattson DC AH/Watt*Hour meters, Kill-a-Watt (230 VAC version) type meters, and a couple inexpensive DC Current Clamp type DMM (Digital Multi-Meters).

This will let your test and evaluate both local and imported devices to see if they will do what you need.

In the US, Utility power is in the range of $0.10 to $0.20 per kWH.... It is not unusual for Off Grid power to be in the range of $1-$2+ per kWH -- Or 10x the cost of utility power.

So, I suggest that you do some costing numbers on your own power... Just some simple math along the lines of:

(price of system + replacement batteries every 5 years + replacement electronics every 10 years + etc.) / (number of kWH to be "used" over next 20 year system life) = $$$/kWH

For example. Say you have the need for a computer. A desktop system + monitor needs 250 watts 10 hours per day. Or a laptop (or other "low power computer option") uses 30 watts 10 hours per day:

• 0.250 kWH * 10 hour * $1.00 per kWH * 365 days = $912.50 per year in annualized power costs for 250 watt system
• 0.030 kWH * 10 hour * $1.00 per kWH * 365 days = $109.50 per year in costs for 30 watt computer system.

The blender, microwave, home water pump, etc. which use large amounts of "peak" power but for only a fraction of an hour per day are, many times, "small potatoes" when compared to the costs of running computers, lights, refrigerators etc. for 10-24 hours per day.

With a couple of meters to measure energy, keeping track of your costs (including maintenance/replacements) over the system lifetime--You can come up with a costing model that lets you make financially sound decisions (that locally available "cheap" computer system vs that low power/high tech. one that has to be imported).

So, that gets back to the Samulex (and others) inverters--Most models have both 120V 60Hz and 230V 50Hz versions available. Obviously, in the US, the 50Hz versions are going to be much harder to find--But the basic comparisons are still valid.

One of the best "small" AC inverters I have seen here is the MorningStar 300 Watt TSW (True Sine Wave) unit. Today, it is only available in 12 VDC (but 120 and 230 VAC versions are both available).

A reason why this guy is so nice for smaller off grid power systems is that it has "search mode" and "remote on/off" input. These are great for having close to grid type power available. For example, you can wire up lots of AC lighting and put the inverter into "search" mode... It will use very little power until it "sees" >6 watt AC load--Then it will turn on. This keeps the power use very low during the day time without you have to manual turn on/off the inverter (most inverters use ~6-20 watts or more just "on" with no loads--for small off grid power systems, this is a significant load).

And the inverter also has a remote On/Off input... You can just hook up a small remote switch (say in the kitchen) to turn on the inverter when you need it without using big (and expensive) DC switches to cycle 60 amps of 12 volt current.

Much of your work will revolve around "conservation"--It is going to be much cheaper to install a smaller off grid power system with energy efficient loads than to try build out a larger system with "what ever bulbs/products" are available locally (sometimes).

-Bill

mike95490

Re: 24v to 12v

Look locally, see if you find golf courses, or warehouses that use electric forklifts. Find out where they get their batteries. That is your battery source.

The "Lister" engine clones from India, are likely your best bet, if you can get a knowledgeable mechanic (you will need one anyway) that can go over it, clean, and adjust it properly. You will need to give it oil at several oil points daily, but it is one tough generator when set up right. I've got more info if you want it. And I run one.

alright71

Re: 24v to 12v

Bill, i appreciate you taking the time to read through what i wrote. It is a strange situation.

The translation group already uses a small inverter system...2 Outback FX inverters, 24-120w panels and 20-100ah batteries. They are currently using around 25 laptops in their translation work.

This is an issue of economies of scale. With an inverter, there are inefficiencies. in a normal, household or small business environment, where generation and consumption can be tightly controlled, inverter efficiencies are not a big deal. What we are dealing with here is a fully off grid, large commercial deployment. A 10% loss when dealing with 3-4,000 watts is what 400 watts...take that and multiply that times 6 or 7 and you will see why i am avoiding passing everything, except fans (12) and laptops (>100) through the inverter. Startup currents in CFLs alone can bring down a system of this size if not planned properly. At home startup currents on CFLs are rarely a consideration.

Everything i can do to eliminate the inefficiencies of inversion even for a small part of the load such as lighting, will go a long ways when multiplied by 60 lights which may or may not all be on at the same time.

Does this make sense? I'm not necessarily talking about the simple question of "how to have lights?" Im trying to illuminate a large number of office, a meeting hall, print shop, and guest house as efficiently as possible. If my power is generated and stored in DC, wouldn't it make sense that to continue with DC instead of converting it and sustaining the 10% losses? Is the convenience and positive voltage properties of AC enough to justify the losses due to inefficiency and accompanying increase of equipment for generation and inversion to cover the losses?

You mention some tools from the US...what is the best way to test a sealed battery to understand it's condition? Is there a load tester for this purpose?

Again, thank you!

Blake

KeithWHare

Re: 24v to 12v

alright71 wrote: »

... If my power is generated and stored in DC, wouldn't it make sense that to continue with DC instead of converting it and sustaining the 10% losses? Is the convenience and positive voltage properties of AC enough to justify the losses due to inefficiency and accompanying increase of equipment for generation and inversion to cover the losses?

You need to compare the inefficiencies for each path.

With AC, you loose some power at the inverter, but 220/240 volts can use standard wiring and standard bulbs.

However, with DC, you need to use larger wires to avoid power loss at low voltage and you need specialized light bulbs, fixtures, etc.

I would lean towards matching the local "standards" so that you buy bulbs locally, etc.

Also, if the site ever gets utility power, there will be less rework if you are using AC.

Keith

BB.

Re: 24v to 12v

Buying sealed batteries (and even used flooded cell) is always a pig in poke type situation.

Probably the easiest is to get a (for example) 12 volt "cheap" AC inverter (typically MSW). in the size you want. Say you wish to test a 12 volt 200 AH battery at 10% of rated current:

12 volts * 200 amps * 0.10 * 0.85 inverter eff = 204 Watts

Connect the Inverter to a set of light bulbs (i.e., 2x 100 watt if they are still available in your area--in the US--arrg :grr) or other device (small electric heater, 3-4 x 60 watt bulbs, etc.).

A good battery should support an 80% discharge (to 20% state of charge). In reality, perhaps discharge to 50% of rated power (~5 hours in this example). and monitor the battery voltage. If it falls below ~11.5 volts in that 5 hour period, it is probably going to have problems.

Then get the battery quickly recharged back to full (don't let it sit for days/week/longer or it will sulfate).

You could also do similar with surge current testing. Any good battery could support C/2.5 load (sealed AGM/GEL batteries should do much better) for 10 second load.

Note, when testing at "heavy currents"--"Jumper cable" types clamps are not going to work. You need full bolted up connections + heavy cables to your test loads.

You can do your testing a battery at a time, or scale up for larger batteries/battery banks.

It is possible to build load banks out of other things (power resistors, old electric heaters, hot plates, motors with fans/pumps as loads, etc.)... I don't know what you have available in your area or your skills (or what local fabrication capabilities are there). Unless you do a lot of battery qualification, anything more than quick and cheap is probably not going to be worth it.

There are some simple/not too expensive automotive battery testers:

http://www.amazon.com/Schumacher-BT-100-Battery-Load-Tester/dp/B000AMBOI0

I believe that this units are typically only rated to do a 10 second test--So they are more of go/no go type test (i.e,. will the battery start the car) and will not test the overall capacity of the battery.

You will probably need to select the current and good/bad voltage point based on your needs and experience--But here is a set of charts that explain what you are looking at:

New poster "leaf" has a really nice set of charts that compare battery voltage against different rates of discharging and charging (as well as resting voltage readings).

leaf wrote: »

Am trying to upload the charts I am using...

Attachment not found.Attachment not found.

I don't quite a agree with the resting voltage line (I think the voltage is a bit low)--But it shows how to estimate a battery's state of charge while operating.

Note, where the charts "flatten out"--the room for error estimating state of charge is pretty high.

-Bill

-Bill

BB.

Re: 24v to 12v

And I agree with Keith--I would highly suggest that you wire for "local" ac (230 VAC 50 Hz) and use inverters/generators.

There are some real issues with distributing lots of low voltage DC power. And high voltage DC power is another huge set of design/safety issues.

Typically, inverter losses are more of a problem with small systems. In larger systems, the losses are (many times) just that 10% issue (build system 10-15% larger and you are done).

If you have, for example, class rooms that are used 10 hours per day--Wire all loads to one inverter/bank and turn off the DC master (use inverter shutdown control--if it has one)--And you have no power off losses when nobody is there.

And run the "rest of the facility" on inverters that are sized for those loads (a smaller AC inverter for night lighting, a larger one for kitchen, etc.).

Are you trying for 100% solar in good weather, or are generators practical for larger loads... Hybrid power systems have been built in Africa before.

Basically, the battery/inverters power the loads night through mid-day. And the genset it powered up for evening meals/studing/lighting/etc. and recharging the battery banks. Can safe upwards of 50% or more of fuel+maintenance costs vs a genset running 24x7.

-Bill

alright71

Re: 24v to 12v

Ok, you guys have me convinced...12v lighting is a bad way to go.

I will wire everything 220v

Thank you all for your help with this one!

I have some additional questions but i will start new threads!

I appreciate it

Blake