Can an HF kit be connected to a 12V battery, then a second HF kit be connected to a second 12V battery, then the two batteries connected in series to yield a 24 VDC system ? Will each battery be regulated independently by the HF controller (If this is even possible)?

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short answer is no that won't work. When you series the batteries together the HF controllers will see it as a 24v battery and either they will burn out or just have a fault. Might just blow a fuse. If you are going 24v then you need a setup that works for 24v. The panel's will need to be in series to get high enough voltage to charge 24v battery bank and you need a charge controller that can manage the higher voltage. My recommendation is a MPPT controller that can take higher voltage and convert to whatever your battery bank needs. Example I have a Midnite classic 150 that can take up to 150 volts and charge 12,24,48 volt battery bank. I have flexibility to modify my setup later.

   I don't think Ray understood, or I don't?

   I interpet the question as can I charge 24 volts using the two kits, and you definitely can as they are, adding nothing. If you put one controllers 12 output to one battery and the others to the second battery each will sense an independent battery and charge. 

   That said there is some complications involved, should each battery be equally down and due to any problem one charge unit put out more then the other we could loose our equal or balanced charge and getting it to return with this type set up will be tough. If one battery system has enough light to fully charge the high battery but the lower battery is shorted of enough light for a full charge you've lost the balance. I don't recommend doing it this way but in a bind it will work, also if we never run the batteries very low as one would just charge longer assuming enough light each day. 

   

Once you put the batteries in series they are no longer 12 volt. Unless what you plan to do is charge them seperately then disconnect the charge controllers before putting them in series. 
If you try to use 12v equipment on a battery bank that has 2 12v batteries in series the voltage will be 24v and you will likely fry something

   You most definitely can run two 12 volt batteries in series and charge them independently, delco built alternators that were 12 volt with an independent transformer to power or charge the second battery. It eliminated the old series parallel switches. We also left the batteries hooked in series full time as there is no need to separate them.  

   If you take a volt meter and put it across either battery when in series, it's still 12 volts and still a seperate battery, just like the 110 leg of a 220 AC grid powered feed. Each leg is 120 to the neutral but across them is 220.

    We used the transformer on the output of 12 volt alternators on diesels that had 24 volt starters but ran the rest of the equipment on 12 volts. Never say a problem in the years I worked on them.

    One set of panels hooked to one battery will charge that battery, and the other will take care of the second  battery. Think of the comon lead tieing the batteries together as neutral on a 220 volt AC grid feed, from it to either high side will be 120 volts, or in this case 12 volts. Across the outside legs will be the 220, or in this case 24. If you take your 24 volts from the combined batteries you still can use either battery or controllers output for your 12 volts, you will have no problem and if some thing frys, it wasn't hooked up correct!

   This situation is quit comon on heavy equipment in cold climates, 12 volts don't spin big diesels fast enough to start without adding heat and or glow plugs. I will back up here, they've gotten far better from when I worked on them with new designs.

     As to the MPPT controller, there neet but expensive! A return on the investment isn't yet there in my opinion, but they do work and work well.

 

Hi Mike,

Here is what you propose, as I understand it:

Yes, each charge controller will safely and separately regulate its respective battery.   That respective battery will also control the front DC outputs of that charge controller.

 

W. R. Wahlquist’s concerns are well founded; batteries in series will perform to the weakest battery charge of the entire string.

 

Do you have a plan for this 24-volt arrangement, or was it just an academic question?

 

Hillbilly Gene

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Hillbilliey that is exactly what I had in mind. While it is an academic question, as I do not have this knowledge stored, it also has a purpose. I am very, very new to this solar stuff and the HF kits seem like a way to experiment and seek experience, especially with folks like the ones on this site. My original idea was if two kit can be put in series to yield a 24V system, can two such 24V systems be put in parallel to increase the current capability of the 24V system. In essence I wondered if four kits could yield an 180 Watt, 24V system. I have a 24VDC microwave and I am simply playing around with it. It has the ability to run at 155 Watts. So I was merely playing with, 'What ifs'. Drawing 155 Watts I was pondering the drain on a battery bank with a pair of in series 12VDC batteries. I did not consider the imbalance pointed out by W.R. Wahlquist that would occur with using four independent panel configurations. It would probably be simpler to use a 12VDC microwave, or even an inverter. Any thoughts on a HF 1200 running a 120VAC microwave. It is a modified sinewave inverter. Will a microwave run off a modified sinewave inverter ? Or, is seeking a DC solution a better option ?

 

   Mr. Gene sure does nice drawings! And is correct.

Hi Mike,

 

To answer your first question: yes, the batteries can be arranged in a series/parallel configuration for a 24-volt bank with each battery being charged by a separate HF kit.  It’s not recommended for the reasons given, but is possible.

 

Inverters:

Every 120v AC device is designed for a pure sine wave, and I cannot, in good conscience, recommend force-feeding a modified sine wave into any AC device except an incandescent light bulb or a toaster.  

 

A modified sine wave should really be called a modified square wave.  Calling it a modified sine wave assumes the wave started out as a pure sine wave and then was modified to a less desirable form.  The Marketing Department is doing it’s best to puff up the product.

 

Comments:

I’m using some of the information in your discussion “24VDC 425 watt microwave” started earlier.

 

First, 425 watts of “cooking power” is the energy going into the food, not coming out of a wall socket (or inverter).  When using that microwave with 120v AC, 5.5 amps are coming out of that wall socket or inverter.  Watts = Volts x Amps, or 120v AC x 5.5 amps = 660 watts.

 

By using a pure sine wave inverter, or any inverter, those 660 watts need to come from the battery.  And using the same formula, those 660 watts translates to a battery draw of 55 amps per hour for a 12-volt battery system, or 27.5 amps per hour for a 24v battery system.  Dropping to 155 watts of “cooking power” will take approximately 2.7 times as long to slowly heat your food (425/155), and you may not be able to adequately cook what you want at that lower power range.  The food simply won’t get cooked if energy doesn’t get to it.

 

 

 

A microwave is really inefficient.  Its sole claim to fame is it does the job quickly, compared to a toaster oven, thereby saving total energy over time.  That “quickness” usually overshadows its inefficiency.

 

Those 660 watts per hour being used has to be replaced by solar.  If you expect to get 4 hours of “good” sunlight per day, then the solar panels should be 660/4 = 165 watts.  That 165 watts are just to replace what the microwave used for one hour, and nothing else, such as “lighting, charging small batteries for flashlights, GPS, radio, cell phone, etc.”

 

Recommendations:

If you intend to use DC to operate that microwave you need a 24v DC battery bank.  Get a MPPT charge controller as Raymond Dias suggests. 

If you intend to operate on 120v AC then get a 1200-watt pure sine wave inverter, because a microwave oven has a surge requirement, and I don’t know of any microwave that will operate on a modified sine wave.  I also don’t believe in operating any inverter much beyond 50% of its capacity, for reliability.

 

Be aware that this entire math is in a perfect conservation-of-energy world, and I have not included the real-world inefficiencies of the solar panels, charge controller, or the batteries, plus wiring losses.  This math is just to get you into the ballpark for minimal requirements.

 

Using solar energy is free and easy if you want a sunburn; it’s not if you want electricity.

 

Hillbilly Gene

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Mr. Gene well put and to the point. I would only add that any brush type motor, skill saw or drill will run on near any wave form as well and infact run well on high voltage D.C..We ran them straight from an automotive alternator by removing the regulator and applying 12 volts directly to the field. Battery removed from the output of course!

Hillbilly Thank you very much for that great reply. I'm just getting interested in solar and from my view it provides energy where the fossil fuels are not available, and power company is not doing its thing. For me survival in an unfriendly world requires food, clothing, shelter and a source of energy. I am gaining information on energy. Thank you.

 

I found http://www.donrowe.com/inverters/inverter_faq.html#modified that repeats much of what you say.  Since where I live I can figure on plenty of sunshine, also when I go camping, it might be something I will continue to tinker with, not for up in the Sierra Nevada mountains camping, but down home in the central valley. The camping part I have concluded solar will be limited to recharging batteries and lighting requirements. I like the microwave for cooking because I find them clean and easy to cook with. I'll look further at taking it and an inverter when I go camping.

 

Thanks for the good information. It took a bit, but I got what I was looking for.

All this information, especially Gene's, as usual, complete and accurate diagnoses, with circles and arrows is all very helpful, but I think no one will know, does it work, or doesn't it work, until you lick you finger and stick it in the wall socket, so to speak...

If the microwave is in your possession, why not charge those two batteries, independently if necessary, so that they both have an overly full charge after resting, connect them in series, connect the MW alligator clips, and try to heat a cup of coffee on high for two minutes....

Worst that can happen is, you drain the batteries in two minutes, this won't "kill" the batteries, just discharge them, like cranking your car engine until the starter starts clicking, they will take a charge again, with no damage, for this one time experiment, or at the very worst, the MW doesn't even start to heat....

Then you will know...I've alwats thought, sometimes, you need to throw caution to the wind to get an answer...

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