Getting 36v from a 12v battery

if your 24v converter has isolated outputs (does not chare negative ground with input), you can combine it with your battery's output to get 36v.

i

snipped-for-privacy@msn.net wrote: ...

You should be able to get a 120v 200w inverter + a 120 - 36v transformer

• a bridge for . You may have to use a couple of transformers in series to get 36v cheaply (e.g., 24 + 12, or 3 x 12). Probably cheaper than 2 more batteries & chargers.

Bob

It just might. 150 watts for 2 minutes four times a day is 1200 watt-minutes or 20 watt-hours per day. Three 5-watt solar chargers (15W total) working on average 2 hours a day (including cloudy and rainy days) more than covers that.

It'd be simpler and cheaper to use three small DC-to-DC (12 to 12) isolated converters as chargers. One or 2 amps (12 to 24 watts) each should be way plenty. A single converter with 3 isolated secondaries would also work. The lowest battery would hog most current -- which would probably be what you want. The converter would only operate when there was solar power available to run it.

On Wed, 28 Mar 2007 23:35:27 GMT, with neither quill nor qualm, snipped-for-privacy@msn.net quickly quoth:

Just remember to put a safety override (a la garage door actuators) on it so you don't start calling yourself Jenny2kids, Jen.

-- We either make ourselves happy or miserable. The amount of work is the same. -Carlos Castaneda, mystic and author (1925-1998) -------

Since you seem to be enjoying the education value of the project :-) wire the batteries in series, and charge them with a proper controller (as little as $35) from PV or a power supply. Solar panels and controllers here

and here It's more than you need, but HF often has a 45W solar setup on sale for $200 Can you say gate lights? :-) This controller is overkill for your application, but I have a barely-used one for $75 if you're interested.

Wayne

Haaa, that's how I got to be Jenny3kids. Just kidding.

Hi Don,

Are you saying to connect their outputs in series to drive the actuator? If that works, might be the best plan.

Hi Wayne,

Yup, you got that right. I have seen the HF 45W units but for a little more than $200 I can get a mule opener all ready to bolt on. I have the bit between my teeth for a unique approach now that I have all these suggestions. Call me a masochist, but this IS getting interesting.

I thank Don for his boat lift philosophy "$20 in parts, $5K if anyone paid for my time."

Thanks for the generous offer on the charge controller but will pursue some more Golberg'ish approaches first.

This has gotten waaaaay to complicated.

Solution l. Use three 12 v. batteries in series. Harbor Freight has solar chargers on sale for $14.99. Buy three, one for each battery. No fancy connections required...

Solution 2. If you already have a big 12 v. solar panel you want to use, again, use the three 12 v. batteries. Build a simple charge pump to generate something over 40 volts (a four stage charge pump should do it) and charge the whole series string together. You should be able to build a 4 stage charge pump for around ten or fifteen bucks...

I'm saying connect 3 batteries in series to drive the actuator, and have three small DC-to-DC converters in series to charge the batteries. The batteries always handle the payload.

This seems to fit because you have only very intermittent load with long periods of recovery time.

These converters could all be powered by your 12-volt solar source. The advantage here is that the converters need only handle charging current, which is a whole lot less than max load current, so they could be quite small and inexpensive. They would only run when solar power is available to run them, while the battery power would always be there to operate the gate.

It could even be a single converter with three isolated outputs if such a thing can be found surplus or whatever. Otherwise, it wouldn't be hard to build one since you seem to be comfortable working with elex.

If you have enough sunshine year-round the 5-watt solar chargers may well be the simplest solution.

Please feel free to email me if you'd like to pursue the other course. I'm retired and enjoy projects like this.

Hi Don,

OK, got it, but isn't that pretty close to what I was suggesting to start with? Have the batteries in series and three solar panels to charge each of the three batteries. I might even be able to use 3 of those 1.5W chargers HF often has for around ten-bucks a piece. I wouldn't need any dc-dc converter would I?

At max load the actuator is rated at 140W, so on a windy day and at max load that may take 2 minutes to close but opening would happen quite smartish and virtually no load with prevailing wind assitance.

The no-load I measured at 36v and 0.7Amps, around 25W for 1 minute (the designed open/close times) which is what it would be with no wind or wind assisted.

Unless I am thinking wrong here, that is 140 / 60 * 2 = 4.6W/hr and

0.5W/hr. Approximately 5W/hr. and easily done with the 3 x 1.5 solar.

We have around 320+ days of sunshine AND we don't do Daylight Saving so that's gotta help too, right??? LOL

Thanks for the offer, but I prefer the forum so everyone can look in and see what's what. Before I ask for suggestions on a project, I always do a google-group search. If we do emails it doesn't get included.

Hi Jerry,

Thanks for the splash of cold water to the face. That's where I started with this except using 5W panels, but after some Math and as you point out, the 1.5W ones will do fine. Besides I already have one of those somewhere, just need two more.

I am still thinking about that pneumatic version. Got a nice ring to it.

With three small solar panels, it is exactly what you suggested to start with. You would not need any DC-DC converters.

It could also be done with a DC-DC converter with 3 isolated outputs, running from your existing 12-volt solar source. However, your initial suggestion of using 3 small panels would be considerably simpler and I see no reason why that wouldn't work very nicely.

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What's that Lassie? You say that snipped-for-privacy@msn.net fell down the old rec.crafts.metalworking mine and will die if we don't mount a rescue by Wed, 28 Mar 2007 17:11:05 GMT:

Could use a DC-DC converter to boost the 12V from the solar cells to

36V to charge three batteries?

Dan H.

On Thu, 29 Mar 2007 15:53:49 GMT, with neither quill nor qualm, snipped-for-privacy@msn.net quickly quoth:

"Hello, Police? I've just found your perp, Jenny12kids."

Around here we have Daylight Saving time more than 6 month of the year, so they should call that Regular Time and in the winter call it Daylight Losing Time ;)

I have seen some pretty simple voltage doubler circuits. Search Google and I'd bet you can find plenty.

I seem to recall a small IC used as a multi-vibrator to pulse the 12 VDC to make it able to drive a small transformer driving a diode bridge. For low wattage, it would be dirt cheap.

Ron Thompson On the Beautiful Florida Space Coast, right beside the Kennedy Space Center, USA

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Hi Clare,

Yeah, but 3 x $15.00 panels from HF is a lot chepaer than buying a charge controller and no wiring issues as it comes with a diode installed.