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Forum Index : Electronics : LT1339 - High Power Synchronous DC/DC Con

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dazz
Regular Member

Joined: 15/04/2008
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Posts: 78

Posted: 09:27am 05 Jun 2008

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Hi All,
Being out of my depth in the area of generator output and battery charging, I have been stumbling around in the dark a bit trying to work through the basics and come up with a plan to build a controller.

I'd rather not use a shunt regulator, for all the reasons that others have already mentioned.
I came across this chip and wondered whether it would be a dumb idea to use it as a basis for a battery charger.

There are links to the specs and an application note below.

http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C10 03,C1142,C1114,P1134,D4162

http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003 ,C1042,C1032,C1092,P1551

The things I like about this chip are that:

It has easy voltage point setting
It has a way to easily limit load current which means it could be set to not exceed the battery specs for maximum charging current.
It has a sync pin so that the internal oscillator can be sync'ed to an external clock. I was hoping to use this to input an MCU pwm signal and so control output current(well at least I hope thats how it works)

The chip also has some other neat stuff like protection against synchronous shoot-through and under-voltage shutdown.

I would set it up as a buck converter for a 24V system.

So, if someone could tell me I'm an idiot now so I don't burn up any more precious brain cells trying to work out how to employ this chip?

Cheers,

Daryl

Edited by dazz 2008-06-07

GWatPE

Senior Member

Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 01:44pm 05 Jun 2008

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Hi dazz,

The area of battery charging is more complex than regulating to a voltage. I would suggest you start with a rectifier from the windmill with a direct connection to the battery. Make provision for a windmill shutdown manual switch on the AC side. Use a commercial battery maintenance component like a plasmatronics PL-20 etc. to control the diversion load, when the windmill produces more power than the battery and normal loads can use. The form of the diversion load will depend on options available, water/air heating etc.

There are many issues with modulators and switching ccts.

If a battery is involved, then my testing has shown that ON/OFF control is more than adequate.

I have only used a modulated type control cct for the windmill maximizing and isolated DC-DC converter on my setup.

I have found that the buck design has high efficiencies at low power levels, where the switching device is at a high duty cycle and doing little work and lower efficiencies as the power level increases and the duty cycle of the switching device decreases.

I still have more work, to perfect a boost/buck design.

I hope to test my concept on a F&P mill. Gordon.

become more energy aware

dazz
Regular Member

Joined: 15/04/2008
Location:
Posts: 78

Posted: 11:11am 06 Jun 2008

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Thanks for the advice Gordon

yeh, it's all very complex. My concerns are probably common and revolve not so much around getting the absolute best out of the mill, although this is preferred. But more the worry that a poor charging system will lead to a shorter life for the batteries. The batteries are a significant part of the RE investment and it wouldn't be good to see them needing replacement in 5 years when a better charger could give them 7 years.

As a matter of interest, have you determined whether the gains from having a MPPT are greater than the losses your seeing in the buck converter?
I presume these losses are in the FET gate switches which I understand can be quite high at higher currents?

Daryl

GWatPE

Senior Member

Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 01:07pm 06 Jun 2008

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Hi dazz,

The main problem with a battery is the changing requirements during the charging process. Commercial units like the plasmatronics PL-20 have inbuilt routines to satisfy the battery requirements. A battery will die quickly if charged to a constant voltage only. I employ 2 stage charging on my battery system. I will eventually make a multi stage charging system.

I hope to modify my battery gridfeed cct to adapt to the source of energy available and adjust to the current state of charge battery voltage.

I am concentrating my efforts on others at present, so my R&D of the F&P will still be a while. Gordon.

become more energy aware

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