Re: charger? (again) deep cycle batteries

On Sun, 28 Aug 2005 07:52:18 -0700, r2000swler wrote:

> "tg" wrote:
>
> <r2000sw...@xxxxxxxxxxx> wrote in message
>
> news:1125187818.105054.150510@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
>> "tg" wrote:
>
> thanks for your response
>
>> Where do you live? City,country, estate?
>
> country (on the edge of surburbia)
>
>> If you are on a "creek"/ stream or
>> have access to a tidal basin water power
>
> no I'm not.
>
>> But powering a motor driven compressor will be a quite a challenge
>> from an inverter. Companies likeTrace make commercial units, but
>> cost out the ying yang.
>
> I saw a 2500W-run/5000W-surge inverter on ebay for about £280. It
> would
> probably be nearer £500 after taxes and shipping, but I think it would
> drive
> a fridge freezer without any problems. (am I wrong?) Fridges don't
> really
> use that much electricity to run. They do need a surge to kick start
> them,
> but I've measured the surge at about 1KVA and it only lasts for half a
> second. I'm thinking along the lines of meat storage in a bad event
> scenario. When faced with starvation a person will eat anything, and if
> one
> was to kill an animal then it could be stored in a freezer and eaten
> over a
> longer period. Being able to run a fridge freezer could mean the
> difference
> between life and death, and this is why I was focusing on such.
> --------------------------------------
> All motors have a much higher start demand then to run.
> Compressors are worse. Our GE combined fridge/freezer
> is rated at 3.2 run amps. I just tested with a peak reading
> amp meter and it draws just over 10A for just over 1.5
> seconds, then drops back to 3.0A.
>
> This is with 120 V not the 240V used in Engalnd. Doubling the
> voltage halves the current so our fridge would draw 1.5A to run,
> and 5A to start. Well within the capacity of the inverter you have
> specified.

What you may not be aware of is "power factor" caused by the heavily
inductive loading of a motor. Just because an inverter is rated at 2x, or
even 5x, the load of a motor doesn't mean that the two can work together.
Inquire of the manufacturer directly and don't guess.

Inverters use a transistorized driver to the primary of an output
transformer. The secondary drives your AC loads. This means that
reflections from the output can be imposed upon the drive circuit.

If you've ever touched the primary of an ignition coil running at 12vdc
and gotten kicked you'll understand what I'm talking about. Even with
12VDC on the primary there's a 600V inductive kick when the points, or
transitor driver, opens.

When your motor-driven appliance turns off there will be a big inductive
kick that, depending on where in the sine wave it occurs, can arc relay or
switch contacts and zap the output transformer secondary. This is coupled
back to the primary and inverter drive transistor bank.

Even if you're at 5% of the drive capability put a very, very good surge
suppressor between your inverter and loads.


> It should be an easy task to rig an adaptor to allow logging of the
> typical run time. I would be tempted to get an older PC to run a BASIC
> loging program to log the on/off times to get a handle on how much
> energy you are going to have to supply. If I get a chance I will do a
> couple of net searches and see if there are any simple DIYs plans for
> this type data logging.
>
>>>From conversations with an electrician frined, he says the chest
> type freezer, the one with a top that opens, is much more efficent then
> the front door style. I can't swear to it, but I think he said the chest
> syle can be up 4 times more efficent. Even double would rapidly pay for
> itself if you're generating your own power.

That's true, the cold air is heavier than ambient. In an upright freezer
that air runs out every time you open the door. Not so with chest
freezers.

> A topic often ignored and fought over is "power factor". Some loads
> appear to draw a lot more current due the pahse difference between
> voltage and current. The big boys, public utilities, spend a lot of
> energy minimising this PF. For a small genset, it can really reduce the
> apparent load. Even thought the mismatch is a mathmatical event, as far
> as a genset or inverter is concerned that mismatch is real energy that
> must be supplied. The original blower in our furnace was a POS crap
> motor that had an awfull PF. While the motor was rated at 5A, a clamp on
> or series ampmeter showed it really drew just over 9A. By adding a
> ~120uF 350VAC cap across it reduced the measured and demanded current
> from 9 to 5. This is mainly a concern with lightly loaded motors, but
> almost all motors suffer from this to some degree. Look up "power
> factor" for more info.
> Terry

Ah, ok, you're up on the technology. Using a capacitor to offset the
power factor helps a lot but to do it right you need to know the
inductance of your load then calculate the capacitance at 60hz(50hz).

Even so huge spikes will occur when turning off the motor appliance that
demands a surge suppressor AKA Varistor. The good thing about varistors
is that they can absorb an incredible load since the surge is so short
time-wise and they can be paralleled to increase the load handling.

-- Regards, Curly
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http://curlysurmudgeon.com/blog/
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