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hmccoy99 Newbie Joined: 12/12/2017 Location: United StatesPosts: 6
Posted: 08:26pm 14 Dec 2017
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Hi all,
New to the forum, I have a EE background and I have been living off the grid for some 25 yrs, I am a full time boater, the system I had before hurricane maria hit Puerto rico 16 6v golf cart batteries. a old original 2.5kw Heart Interface modified sine wave wave inverter with 1500 watts of solar and two 600watt wind generators with a outback solar charge controller. my loads are water maker one 1hp for 2=3 hrs, every couple days. freezer 1/2 hp cold plate design 2 hrs per day. microwave . etc. the old heart interface inverters finally died from salt water bath. my system was 12v and not too efficient. I am in the process of rebuilding the electrical system on the boat. i have two 2.5kw heart systems and was thinking of re using the transformers to make a 5kw sine wave inverter. I have been reading the posting of several excellent post of the subject building from scratch. i realized the E core type of transformer would not be a efficient but would like to proceed anyway. idle current losses are not as much of a issue as load carrying, cost and reliability.
so I would like some feed back and using 15kw power jack power boards and driver board EGS002 with some of the upgrades presented on this forum. of voltage control and current control. I welcome all comment of the approach. so i can benefit from the experience gained from this group.
Henry
Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498
Posted: 01:06am 15 Dec 2017
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Hi Henry,
You would need to change the gate resistors on the Power Jack board.
If your battery bank is 48 V you need to have a primary winding for 26-28V and half that for a 24V battery. Your transformers may have a different winding voltage being square wave, so you may have to rewind them to get it to work.There are only 10 types of people in the world: those who understand binary, and those who don't.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 11:02pm 16 Dec 2017
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This is starting to look like a pretty serious system, and well beyond 12 volts I am thinking.
You will probably still need twelve volts for most of the "boat" things that run directly off dc.
But all the serious inverter driven stuff would benefit hugely from a separate 48v main battery and a higher voltage dc system ahead of the inverter. It would then be fairly easy to charge the 12v battery from the larger 48v battery via a buck converter when the engine is not running.
It should not be too difficult to reconfigure your existing solar panels and battery cells for 48v, and work from there.Cheers, Tony.
hmccoy99 Newbie Joined: 12/12/2017 Location: United StatesPosts: 6
Posted: 06:49pm 17 Dec 2017
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Thanks for your comments Tony,
yes i have taxed the 12 volts system heavily 2500 watts is about the max one can get from a 12v system. the transformers are large and wound with heavy wire about 40 pounds ea. the heart inverter seems very simple design. with a center tapped primary switching each leg. with 12v. I need to find the voltage ratio. I have limited test equipment on my boat. unlike the shop/lab i had in the past. I think E core transformers are more forgiving in design requirements. than toroids. what is your opinion of this board:
hmccoy99 Newbie Joined: 12/12/2017 Location: United StatesPosts: 6
Posted: 06:54pm 17 Dec 2017
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Hi
does anyone make a control board that is easily integrated into the power jacks main boards? with some of the design improvement identified on this forum?
Henry
hmccoy99 Newbie Joined: 12/12/2017 Location: United StatesPosts: 6
Posted: 07:13pm 17 Dec 2017
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Yes I agree 48v system is better, 200 amp copper losses add up fast..for 2500 watt system 2/0 wire limited to short runs where i use 4/0. with 12v primary wire.
and to ask those mosfets to switch any more than 200 amps is just asking for problems. IR losses much less with higher voltage for sure. I have seen some power board designs with 12-16 mosfets per leg. I dont think that is good design practice without carefully matching the mosfets i think one could have a cascade failure caused by unbalanced current in each mosfet. Its sure a design challenge as the power level goes up.
henry
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 08:31pm 17 Dec 2017
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There are quite a few issues to consider. Inverter technology is continually evolving and is usually best to "run with the herd". There are usually very good reasons for choosing the various approaches and topologies in current fashion.
As you have pointed out, conduction losses rise at a rate of current squared, so higher voltages and lower currents are definitely the way to go when moving to seriously higher power outputs.
Push pull with centre tapped transformer is now old technology best suited to lower voltages and low frequency square wave inverters, where the turn off voltage spikes generated in the primary are tolerable, and can be dealt with. Its definitely not going to work with high frequency PWM.
Full bridge operation is now pretty much universal, because the mosfets never see voltages beyond the supply rails, which is a very important feature.
The problems with E and I laminations are that the material is usually of a low grade which is both lossy and has a lower permeability meaning that the zero load idling power will be quite high and the voltage regulation not so good.
Toroids are vastly better in every respect, they are just more difficult to wind. The main thing is to not run the flux density too high, give it plenty of turns, and that will reduce idling power and reduce the initial turn on surge, which can be a mosfet killer.
Working out the required transformer ratio is fairly straightforward. It will need to be able to reach the sine wave voltage peaks at minimum battery voltage, allowing for some additional voltage drops due to conduction loss around the whole system. The logic goes something like this:
Nominal battery voltage 48v Expected minimum usable battery voltage 40v Voltage available at the mosfets after allowing for some resistive losses 38v Peak voltage reachable at the primary winding 38v RMS primary rated voltage 38v x .7071v = 27v
So you might wind your transformer with 110v/220v secondary and a primary voltage around the 26v to 28v region.Edited by Warpspeed 2017-12-19Cheers, Tony.
hmccoy99 Newbie Joined: 12/12/2017 Location: United StatesPosts: 6
Posted: 06:05pm 19 Dec 2017
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thanks Tony
I am curious what are the pro and cons of modultion configurations? unipolar or bi-polar I have seen commerical board configured both ways. what is your opinion?
henry
hmccoy99 Newbie Joined: 12/12/2017 Location: United StatesPosts: 6
Posted: 06:17pm 19 Dec 2017
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the two methods:
• Unipolar modulation: The carrier changes between 0 and a positive peak (Cm); the reference is always positive; and the PWM output switches between 0 and 1;
• Bipolar modulation: The carrier is symmetric about zero, with a amplitude equal to Cm; the reference is a sine wave without DC offset; and the PWM output switches between −1/2 and +1/2.
henry
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 07:50pm 19 Dec 2017
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Unipolar is probably more convenient when it feeds into the usual step up transformer, a PWM filtering choke is only required on the high frequency side. The low frequency side can drive the other end of the primary directly.
An alternative to that might be where the inverter is fed from high voltage dc, say for example >160 volts dc. A bipolar system could then provide a 110 volt rms output from each side of the bridge producing 220v between the two separate filtered outputs.
That might be more convenient as no output transformer is required, but it does requires two PWM filtering chokes.
Not using an output transformer becomes much more efficient, especially at very low output power percentages. Providing a high voltage battery is not without its own problems, including safety issues. But it would make for the smallest and most efficient inverter system possible because its all high voltage low current. Cheers, Tony.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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