60 Hz inductor design?

I want to reshape the output of a 115v "modified sine wave" inverter so as to allow it's use with a 19.2 v NiCad battery charger which refuses to work with the raw inverter output. Using Spice I find that an inductor input singly loaded Tchebeyscheff filter would give a much improved sine waveform. The current thru the 237mH inductor appears to be 3amp pk with of course a very distorted voltage wave of some 190 v pk. Is it ok to use power transformer core of the above VA and assume that since there is no secondary there will be twice the winding area available. Since the inductor Q is max when conductor loss = core loss does this mean that the optimum core for an inductor will have a smaller winding window than that of a trnsformer of the same VA? I use a 19.2 v Sears drill to raise the sail on my boat and want to recharge the battery from ship's power (12v). Dick

Reply to
rqlhgl
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How did you model the battery charger as a load on the filter in spice?

In most transformer designs, the primary and secondary windings each use about half of the window area, if that is what you are asking.

A better way to look at the Q problem (since you may not have all variables available, like arbitrary core size) is that highest Q occurs at lowest total losses. For a given core, the copper losses are lowest by filling the window with copper. Also for a given core, the losses are lowest for lowest core flux swing. So adding air gap to the flux path should give the lower core loss. But that also lowers the inductance, requiring that filled window to have more turns (of thinner wire) to restore the inductance, which raises the copper losses. So the main balancing act is between lowering the core losses with gap while raising the copper losses.

Hitting close to the true minimum loss takes either some experiment or considerable math.

I doubt that a good sine wave is needed to make the charger work. I suspect that the fast edges of the modified sine wave inverter are just confusing the control circuit in some way, and just some simple low pass filtering will suffice. But I have been wrong lots of times.

Reply to
John Popelish

To Fred: I want to take advantage of the existing (already paid for) quick charger which has 4 contacts to the NiCad battery and senses battery temperature. I suppose I could build a 12/~24 v dc-dc converter, say one that adds 12v to the existing 12v but then I would have to also build in temperature and float voltage programming to match the existing charger. The bit about the boat is relevant to the fact that 115v sinusoidal suppllies for boats start at about $600 and the drill plus charger was only $99, it is thru making such choices that I preserve my "economic status".

To John: I assumed that the charger input impedance was V*V/W where the charger power is stated to be 75w, this gives 176 ohms. I figured that non-linear deviations from this assumption would be mitigated by the

20uF shunt capacitor of the filter. I just bought an old Kiusui 'scope on EBay and hope to take a look at the inverter output and the charger input current via a home-brewed current transformer. I've been retired 15yrs and sure miss having a lab full of equipment. Thanks for your interest, Dick
Reply to
rqlhgl

Reply to
Paul Mathews

What are you running the inverter from?

Might it not just be easier to charge batteries from the original source? This is a simple boost converter.

There are also lower-voltage drills.

RL

Reply to
legg

It would be simpler to convert the inverter output to DC, voltage doubling if necessary.

[snip]

What does that have to do with anything other than to boast about your economic status?

Reply to
Fred Bloggs

Reply to Legg: I guess my Dec 4 1:38 pm reply crossed your's, I have 2x 115 ah 12v batteries. I need the 450 in lb torque of the higher voltage drills even running it in low gear and reverse to take advantage of the 2:1 gear ratio of the 2 speed winch. Reply Paul: I am going to wait and see what the 'scope reveals,(if it works at the @21.50) I paid. For the Spice simulation I assumed that the "modified sine wave" inverter output would have a 115v rms value which translates to about 150v pk. Surplus 2amp Corcom line filters can be bought for

Reply to
rqlhgl

That charger might run on 160 volt DC. It probably just takes mains power, runs it through a bridger rectifier and runs off that.

Reply to
kell

Any decent charger should work over a range of mains voltages, usually down to 100V or less for a 120VAC charger. Consequently, I'll be surprised if slightly less peak voltage poses any problems. If you end up needing to do heavy filtering for some reason, there are passive PFC chokes readily available, possibly in surplus. If you get desperate for sources, let me know, and I'll send you some large powdered iron cores and instructions for winding suitable inductor(s). I'm a boater on a budget, myself, and it cracks me up how people assume that anyone with a boat must be wealthy. Paul Mathews

Reply to
Paul Mathews

One of the significant factor in my purchasing Dewalt cordless tools some years ago was the availability of a 12V DC input charger that works with most all of their batteries, including the 14.4V ones, as I was going to be spending time out in the middle of nowhere, I mean, New Zealand :-), with all of a 50W 12V solar panel for power.

Something to keep in mind if you start losing enthusiasm for your initial approach here... (and since it's a sailboat, power efficiency probably is a concern as well -- I'd rather go through one power conversion than two...)

Reply to
Joel Kolstad

Inside the battery charger there is undoubtedly a transformer and rectifiers. Why not see what that DC voltage is when running on mains, and then replicate it with a simple DC-to-DC boost converter on the boat?

Reply to
Don Foreman

Or else the charger is a switcher that takes mains power, rectifies it straightaway and runs off high DC voltage. Either way, you'd need a step up in voltage. Just a question of how much.

Reply to
kell

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