Batteries, Chargers, and Converters

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Batteries, Chargers, and Converters

Postby 48Rob » Tue Dec 20, 2005 7:04 pm

I'm afraid I'm having a senior moment...actually several of them...
My electrical system is pretty darn simple, but switching from battery power to the converter has me scratching my head.

Currently I have two 6 Volt batteries wired in series to produce the needed 12 Volts.
The leads from the batteries connect to my fuse panel, which sends it to various circuits.

I just installed my new battery tender

Image

and hard wired it to the batteries.
As I understand it, there is a one way switch (electronic thing?) that keeps the power from running backwards out of the batteries and into the charger, so that part isn't a concern, but!

Now I'm ready to install my 12 volt converter (power supply unit) and am confused as to the best (simplest-easiest) way to isolate the batteries when using the converter to power the items the batteries normally would.

I don't want the converter to pump juice into the batteries when I have shore power.
Is there an easier way than running a bunch of switches that must be manually thrown each time the power source is changed?


Thanks.

Rob
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Postby mikeschn » Tue Dec 20, 2005 7:12 pm

I used a switch... I don't know of an easier way...

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SPDT

Postby Dee Bee » Tue Dec 20, 2005 8:49 pm

I think what you will find useful is a single pole double toggle switch or SPDT. This kind of switch allows you to connect two sources to the switch, but only one or the other is connected electrically to the circuit as determined by the throw of the switch.

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Postby GeorgeTelford » Tue Dec 20, 2005 8:54 pm

Hi Rob

What are you going to run in the tear thats over 6 Amps?, with the minimal gear that I have seen included in most tears, I cannot see the point of having a convertor too, the charger being 4 stage would cover you, and on the rare (if any) times that the tear uses over 6 Amps the battery would supply. Maybe I am missing something?
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Postby madjack » Tue Dec 20, 2005 9:26 pm

Rob, one of the nice things about the Deltrans unit is that it is rateed as a PS also. So as George sez, any juice needed upto 6 amps will be supplied by the Deltrans...anything over will be pulled from the battery...George said it and if you read up on the Deltrans you will see that they say it also...
madjack 8)

p.s. if you really want to use the convertor, the spdt that Dee is talking about is probably the best way to go...they do make auto-switching units but they are pricey...especially compared to the buck 2.98 that the spdt would cost ya
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Postby TomS » Tue Dec 20, 2005 9:43 pm

madjack wrote:Rob, one of the nice things about the Deltrans unit is that it is rateed as a PS also. So as George sez, any juice needed upto 6 amps will be supplied by the Deltrans...anything over will be pulled from the battery...George said it and if you read up on the Deltrans you will see that they say it also...
madjack 8)


I have the 6 amp Deltrans in my tear. I didn't know it was rated as a power supply. That is really good information. Thank Madjack.
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Postby madjack » Tue Dec 20, 2005 9:59 pm

Tom, the tech data PDF states, that it is a ".....high frequency switching power convertor with true DC sine wave power of 70 watts (12VdcX6A)"....it also says a whole buncha other stuff
http://www.batterymart.com/pdf_files/De ... TENDER.pdf
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Postby 48Rob » Wed Dec 21, 2005 11:42 am

Mike, Jack, Dee, & George,

Thanks :applause: :applause:

Somehow I was thinking of a lot more complicated switch array...

Senior moment thing...older I get, the more I forget...this isn't the first wiring work I've ever done...

I missed the power supply rating, but that's great.
I was rather concerned with running the (less than cheap) LCD television off the charger, but now it looks like it won't hurt it.

Or is that correct?

If the draw is larger than the 6 Amps (5.833, from the 70 Watt stated output...though it also says 5 Amp max??) the charger/PS. puts out, then as you stated, it will draw reserve from the battery bank.
If it draws it too low, will it not "starve" the TV of needed amperage, and do harm? :cry:

Perhaps this is stretching the scenario too far, as obviously I shouldn't draw off more than half the charge...

My calculations show that I'll need aproximately 13.68 Amp hours per day.
So, at that rate, drawing from a 105 amp hour bank @50%, I can reasonably expect to get three full days worth of power from the reserve (41.04 Amp hrs from the reserve of 52.5)

Do these calculations look right?
If they are, then there probably isn't a need for a power supply in addition to the charger...whis is really good, cause I can think of a lot of other things to spend the money on!!


Galley lights, 9.72 Watts=0.81 Amps x 1 hr=.81 Amp hrs.

Cabin Lights, 84.0 Watts=7.0 Amps x 1 hr=7.0 Amp hrs.

TV. 12.6 Watts=1.05 Amps x 2.5 hrs=2.62 Amp hrs.

DVD, 10.8 Watts=0.90 Amps x 2.5 hrs=2.25 Amp hrs.

Water pump, 24.0 Watts = 2.0 Amps x .50 hrs =1.0 Amp hrs.

Total Amp hrs needed per day is 13.68.

These calculations are slightly flawed in that the rated Amp draw on the pump is 5.0 The above Amp draws are actual, but the pump was spinning free, not actally pumping water, so, I may need to add 1.5 Amp hrs per day, or 4.5 extra Amp hrs to the three day total, which puts me at 45.54 Amp hrs.

Now, on another note;
If my two 6 Volt 105 AH. batteries won't supply enough Amp hrs for an extended trip, I can replace them with two 12 Volt 105 Amp hr batteries, and gain 52.5 Amp hrs of storage capacity, right?

I'll be doing some tests this weekend to see just how accurate the numbers are by running lights, etc to see how long the batteries will last.

And as a final note, I was concerned about the power draw from the TV. and DVD when they were not being used. (I have them both switched).
When doing the Amp draw tests, I found that the "at idle" draw of the TV, and DVD (both 12 Volt of course) was significant, at least in the finite world of 12 Volt storage batteries...

The TV draws 0.18 Amps = 2.6 Watts

The DVD draws 0.14 Amps = 1.68 Watts

Total of 4.28 Watts, 0.32 Amps

Though it only comes to 1 Amp hour used in a three day period, it amounts to a lot if you need that hour.


Rob
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Postby GeorgeTelford » Wed Dec 21, 2005 12:35 pm

Whoa, hold on there Bald Eagle, back up a little.

Is the TV rated as portable? ie does it come with a cigarette lighter lead to run off 12v ?

Just because the wallwart is a 12v power supply this does not automatically mean that it will run from a leisure battery, consider a 12v battery that reads 12v is actually Flat... It should normally read 12.8v that is 6.6% higher than 12v, but if the charger is on then the power could be as high as 15v and that is 25% higher. This may be a problem if the item is not made to be used via automotive battery power.

Is it a tiny screen LCD?


BTW Ampage is drawn not pushed, consider a starter battery this can supply 150 Amps + to the starter motor, if it was being pushed a small bulb would blow if 150 Amps were pushed through....
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Postby madjack » Wed Dec 21, 2005 3:18 pm

...Rob, I know the PDF is a little confusing because it contains a whole bunch of info...some relevant some not. It also contains info on discontinued models, which is were the confusion comes in...I think(?) the 5A output is for an older model(?)
I think that here in the USA, that if the appliance is rated at 12V, it is "automotive" rated...that would be a general assumption by the public and the manufacturer should know that assumption would be inferred...
the only exception to that would be if the unit were meant to be powered by a PC power supply,( ie. a PC monitor)...
if you can find some real technical data on the unit(like form the manufactures website) it will probably indicate a voltage range from say 10/13Vdc.
As George stated electricty is "drawn" not "pushed" so the battery/PS combo would only supply what power is needed
madjack 8)
p.s. your calculations on usage and need are correct as far as I can tell
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Postby TomS » Wed Dec 21, 2005 3:28 pm

It just shows to go ya, it pays to RTFM! :lol:

madjack wrote:Tom, the tech data PDF states, that it is a ".....high frequency switching power convertor with true DC sine wave power of 70 watts (12VdcX6A)"....it also says a whole buncha other stuff
http://www.batterymart.com/pdf_files/De ... TENDER.pdf
madjack 8)
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Postby madjack » Wed Dec 21, 2005 3:45 pm

TomS wrote:It just shows to go ya, it pays to RTFM! :lol:

madjack wrote:Tom, the tech data PDF states, that it is a ".....high frequency switching power convertor with true DC sine wave power of 70 watts (12VdcX6A)"....it also says a whole buncha other stuff
http://www.batterymart.com/pdf_files/De ... TENDER.pdf
madjack 8)


Tom, about 20 yrs ago I learned a very valuable RTFM lesson...several friends with kids had bought swing sets one Christmas...myself and another buddy were designated as the "assembly mechanics"...neither of us had ever put a swing set together...on the first unit, we just dumped all the connectors in a box and started fitting things together...after several hours and much hair pulling we finally had the swing together...after finding and following the directions...forthe next 3, we left the connectors in their bags and folowed the directions and lo and behold, we cut the time for assembly/frustration by about 75%...lesson learned...RTFM
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Postby 48Rob » Wed Dec 21, 2005 4:26 pm

George,

The TV. does not make clear the acceptable voltage range in the literature, or on the Web site (it was purchased on E bay).

It came with a +12 volt power supply (plug in transformer).

The back of the monitor states "Voltage 100-240VAC"

The DVD (different company) states +12 VDC.
It does not state a range, but is manufactured for use in an automobile, so as Jack stated, it should... accept the potential range of voltages.

The TV is another question...

I have played it for about 6 hours so far with no apparrent damage...but just from the batteries, not with the charger.

It is a combo TV computer monitor, 15.2"

Image
http://shinmong.en.ec21.com/GC00741343/CA00741372/15.2_LCD_monitor_TV_(SMT-152TW).html
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Postby madjack » Wed Dec 21, 2005 4:56 pm

...the TV is definitely another question...I went to their website and could find no other info, other than they sell units for autos and home...yours is a home unit...I don't know if the line voltage fluctuations would adversely affect it but your home power will vary from 110+- to 130+- , so that would affect the output from the transformer...it seems there would be a variance that is acceptable regardless of input source...I guess all you can do is try it out and hope for the best (or worse $> )...the one positive thing is the fact that the Deltrans unit is supposed to put out true/clean DC power, all the damage done to electronics that I have heard about came from having a "dirty" DC input coming to them
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Postby 48Rob » Wed Dec 21, 2005 8:54 pm

Hi Jack,

It really isn't all that important, I was just trying to be accurate... :thinking:

GENERAL DESCRIPTION: The Power Tender PLUS battery charger is a microprocessor controlled,
high frequency switching power converter that has a true DC output at a maximum power level of
approximately 70 watts.


It could well be that I misread something, the other part was a UL limit of 5 Amps.

Thanks for all the help, I'll proceed carefully...if the TV fries, well, then I supppose it will be another lesson learned... $>

Rob
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