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Thread: Saturday at home, installing an inverter

  1. #101
    Diamond Member AndyD's Avatar
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    Yes, the depth you cycle you battery to will have a pronounced effect on the number of cycles in it's lifespan. Most batteries have predictive lifespan graphs available from the supplier where you can predict the number of cycles your batteries will survive and, from experience, they're fairly accurate if you're using a good charger and perform very basic maintenance.

    13.1 volts sounds a little high, usually fully charged is just under 13 volts and the 50% discharge voltage is around 12.1-12.2v. Gel batteries are usually a little higher voltage that lead acid though. Using voltage to check battery charge is prone to innacuracies if the battery has been under recent charging or load conditions and temperature can also have small effects on the reading. You should never discharge a deep cycle leadacid battery below 12v as a rule of thumb which will by 75% discharged at that point. Also try not to leave the batteries in a low state of charge for any length of time, obviously if you're only using solar or wind to recharge them it might be unaviodable but in that case select batteries accordingly.
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    i see the axpert default cut off dc voltage is 21 volt on the 24 volt 3kva. the 48 volt 5 kva default setting is 42 volt. i wonder why they set it so low.

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    Quote Originally Posted by tec0 View Post
    It is crazy that "ALMOST" no websites have prices when it comes to solar stuff.
    I have always wondered why a lot of websites never put prices for their products. In a sense you end up wasting a potential customers time and company time, as they have to email or phone for a price.

    On another note
    High demand has pushed up inverter and battery prices, but as more suppliers join the market(in hopes of making super profits)it will lead to a decrease in price.

    During power cuts my only need is lighting(gas stove). I bought a cheap chinese inverter 100W(R100) 50amp Battery (R800) Battery charger(R350) and runs three 11W lamps for about 7 Hours. Being using the setup for about 2 months now(Twice a week).

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  5. #104
    Diamond Member Justloadit's Avatar
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    Quote Originally Posted by bergie View Post
    i see the axpert default cut off dc voltage is 21 volt on the 24 volt 3kva. the 48 volt 5 kva default setting is 42 volt. i wonder why they set it so low.
    This is so you get the so called time of operation on the brochure. Following this route means that after approximately 30 cycles, your battery is dead.

    I have had a problem with one of my customers, precisely because of this. He reckons the China Mall Solar inverter and charger is better than mine, because it runs for 2 hours longer than mine. What he does not understand is that my unit cuts out at 11.5V thereby prolonging the battery lifespan, as opposed to the competitive unit cutting out at 10.5V. I am now waiting and hoping for him to come back after his battery is dead and reverse his statement.
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar pumping, Solar Geyser & Solar Security lighting solutions - www.microsolve.co.za

  6. #105
    Diamond Member Justloadit's Avatar
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    Quote Originally Posted by IMHO View Post
    How long, in years, can a battery last? The Deltec 1250 claim 2000 cycles at 10% DOD. If one is using it strictly for power outages say 3 times a week at less than 10% DOD, you will cycle it 156 times a year, which means you should be able to do it for 12.8 years. (2000/156).

    Is this possible? Is the battery not going to pack up before that from age alone, never mind the cycles?

    I suppose it could be possible if you do maintenance on the batts, but you cant, as it is sealed units.
    The majority of batteries have a 5 year lifespan, unless you specifically look for and purchase a long life battery. You guessed it, cost is far much higher.

    With respect to measuring the battery capacity, it is possible, but you require some very expense electronic equipment. I have been looking for one for a while, and found one at RS. ACT Battery Tester
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar pumping, Solar Geyser & Solar Security lighting solutions - www.microsolve.co.za

  7. #106
    Diamond Member tec0's Avatar
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    I got hold of my old electronics books and sure enough i have something that might actually work and it will not cost me anything close to what we are being charged commercially. I just need to proof concept and if i don't set my workbench on fire or end up extra-crispy i will share the build. Oh this is going to be fun playing with 220 Volts and a Amp potential of almost 8 Amps and up...

    yea... some proper PPE will be a must...
    peace is a state of mind
    Disclaimer: everything written by me can be considered as fictional.

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    Diamond Member AndyD's Avatar
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    Quote Originally Posted by Justloadit View Post
    This is so you get the so called time of operation on the brochure. Following this route means that after approximately 30 cycles, your battery is dead.

    I have had a problem with one of my customers, precisely because of this. He reckons the China Mall Solar inverter and charger is better than mine, because it runs for 2 hours longer than mine. What he does not understand is that my unit cuts out at 11.5V thereby prolonging the battery lifespan, as opposed to the competitive unit cutting out at 10.5V. I am now waiting and hoping for him to come back after his battery is dead and reverse his statement.

    The Axpert inverters don't really give time of run figures in their brochure, the only time they give these kind of figures is in the owner/installation manual which contains a quick guide to suggested battery bank requirements but this isn't sales type info.

    Quote Originally Posted by bergie View Post
    i see the axpert default cut off dc voltage is 21 volt on the 24 volt 3kva. the 48 volt 5 kva default setting is 42 volt. i wonder why they set it so low.
    The default setting is too low for my liking as well and I always set them higher. I did mention this issue somewhere else on the forum, maybe even on this thread (I haven't searched) but it's just one of the perameters you've got to set up when installing them. Also that cut-off voltage is being measured when the batteries are under load and I'm guessing it would be an uncompensated value so the figures in my last post won't necessarily apply.
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  9. #108
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    I have just purchased my very own inverter - works like a dream.
    tec if have the time to "build" your own inverter, good for you - I look at it entirely different. Secondly if you build you own inverter and your house burns down or something happens, insurance will certainly not cover you !

  10. #109
    Diamond Member Justloadit's Avatar
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    Quote Originally Posted by tec0 View Post
    I got hold of my old electronics books and sure enough i have something that might actually work and it will not cost me anything close to what we are being charged commercially. I just need to proof concept and if i don't set my workbench on fire or end up extra-crispy i will share the build. Oh this is going to be fun playing with 220 Volts and a Amp potential of almost 8 Amps and up...

    yea... some proper PPE will be a must...
    There are many circuits on the web, but all small stuff, and most of them are square wave, and probably involve a transformer which is driven at 12V and steps it up to 220V.
    When you talk the large inverters, usually 2KW upwards, they tend to be pure sinewave, as there is no saving in the electronics by going modified sine wave. Whilst the H bridge to generate the sine wave from a DC link of 400V is relatively easy to get right, as opposed to converting/boosting the battery voltage from 12/24/48V to 400V link becomes another mission. Efficiency at these high power levels starts biting hard on your available battery energy. The biggest cost factor is the switching devices on the low end, along with the isolating transformers, along with respectable rectifying diodes which can handle the relatively high frequencies that one wants to use to reduce and improve the cost on transformers. This is where the heat of any inverter lies.

    Anyway good luck and have fun. When you finished, you will see that the prices may not be so outrages as thought on first glance.

    As a matter of interest, I am currently looking at FETs which can switch 46A at 1200V at frequencies above 500KHz, with switching on times of 25nS and switch off times of 42nS and an on resistance of 85milli ohms. The only issue here is that they cost over R1K each. For the techies this is really a super new device. Lets just do simple calculation, lets say that we are using it in a 3Kw inverter, which translates to approximately 13Amps flowing through the device when it is on, so loss or power = Amps^2 * resistance.
    13*13*.085 = 14.3Watts. Now in heating terms, this will be a very small heat sink, because heat is to the power of 2 when one needs to dissipate this heat. Lets take a current FET which would work in the same environment as the FET discussed, which has an internal on resistance of 427milli ohms. doing the same calculation as above,
    13*13*.427 = 72Watts. The heatsink required to keep the device cool will be very large with a fan. This is almost as much energy a modern LCD TV uses.
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar pumping, Solar Geyser & Solar Security lighting solutions - www.microsolve.co.za

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  12. #110
    Diamond Member tec0's Avatar
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    Quote Originally Posted by Justloadit View Post
    As a matter of interest, I am currently looking at FETs which can switch 46A at 1200V at frequencies above 500KHz, with switching on times of 25nS and switch off times of 42nS and an on resistance of 85milli ohms. The only issue here is that they cost over R1K each. For the techies this is really a super new device. Lets just do simple calculation, lets say that we are using it in a 3Kw inverter, which translates to approximately 13Amps flowing through the device when it is on, so loss or power = Amps^2 * resistance.
    13*13*.085 = 14.3Watts. Now in heating terms, this will be a very small heat sink, because heat is to the power of 2 when one needs to dissipate this heat. Lets take a current FET which would work in the same environment as the FET discussed, which has an internal on resistance of 427milli ohms. doing the same calculation as above,
    13*13*.427 = 72Watts. The heatsink required to keep the device cool will be very large with a fan. This is almost as much energy a modern LCD TV uses.
    yea my thinking was basically using a none conductive oil cool... Might work right... "same type of oil used to submerge PCs in. Think it is mineral oil not sure i have notes on it on my server will have a look get back to you on that. I know it is said that it doesn't do a good job at cooling stuff but that was the idea...

    Quote Originally Posted by Justloadit View Post
    FETs which can switch 46A at 1200V
    do you have fact sheet on them if you don't mind please.
    peace is a state of mind
    Disclaimer: everything written by me can be considered as fictional.

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