adding timer on inverter power+ to avoid draining battery

[Jared1048]

I just realized that plugging my cell phone into a 2500watt inverter pulls the same amount of power than if it were hooked up to the refrigerator! That sucks. Guess I'll have to buy a small one for the little stuff.


While seeing this got a little worried about leaving the inverter plugged in over night and having it drain my house bank. Seeing this could really screw me id like to put some type of timer device on the power side of the inverter to disconnect the connection to the house bank after a set time. Max time around 4 hours would probably be more than enough since I'd I'll be running it to power the 120v refrigerator

I can't seem to find something that will fit the bill though. Im not an electician so my searching capabilities are limited to my lacking words.


Anyone know the names of these contraptions?!

Thanks as always!
Jared

 

[Sumner]

This is what I'm going to do and I must stress that at this time I haven't done it except for buying the parts.

I bought some of ...

...the above low voltage switches off of e-bay for ...

http://www.ebay.com/itm/Sure-power-low-voltage-switch-130512-/250889307420#vi-content

...about $10.00. They are used, new are about $75.00. You can adjust the voltage that they cut the circuit you want to use in and out. I'm going to try about 12.3 volts on a circuit or two to some fans to circulate air on the Endeavour when we are gone. So hopefully if the solar is working and the voltage is over 12.3 then the fans will be on and if it goes below 12.3 the fans will go off.

Hope to have this wired before we leave the boat in 2-3 weeks and will post later on our site the mod and if we are happy with it or not.

I'm sure there are other options out there, but if this works it isn't very expensive. According to this...

http://www.waytekwire.com/datasheet/80029.pdf

... they will handle up to a 20 amp load, so you need to be below that. In our application the load will be less than 1 amp. Not sure what your load will be, inverter plus frig, and you could be well over the 20 amps so be very sure of what you are doing. If the load is over 20 amps the switch could control a solenoid that could handle the load.

Also the charge on the battery has to go over 13.0 volts for it to reset and turn the circuit back on.

On the phone just get a 12 volt charger for it,

Sum

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[Maine Sail]

Look up the Sure Start LVD (Low Voltage Disconnect) switches. I think they are still made by Cole Herse. They have them in high amp models and IIRC cut off the voltage at about 12.0-12.2V..

Unfortunately I have to ask why you want to charge a phone via inverter when DC charger are available from Wal*Mart or on-line for about $8.00? A fridge through an inverter can also suck a lot of current at 12V..

The DC amp draw will be roughly 10X what the rated AC amp draw is. So 5A at 120V is 600W that same load on DC through an inverter will look like:

600W / 12V = 50A X inverter inefficiency of 20% = 60A DC to run a 5A/600W rated 120V fridge.. If you can tell us what the fridge is we can give you a more accurate load..

 

[Don S/V ILLusion]

Re: adding timer on inverter power+ to avoid draining batter

I'm still struggling past the first statement that

"my cell phone into a 2500watt inverter pulls the same amount of power than if it were hooked up to the refrigerator".

It sounds like you are trying to solve an inconceivable problem.

 

[weinie]

Re: adding timer on inverter power+ to avoid draining batter

Can't you use a DC (cigarette lighter) charger to charge your phone? You could also just get a cigarette lighter type USB charger too.

 

[Mike B1026]

Re: adding timer on inverter power+ to avoid draining batter

Yep, the OP is wasting a lot of juice by converting DC to AC, then back to DC.

 

[Jared1048]

Yes, i do need to get a smaller inverter for the cell phone.

Those low voltage cut offs look like they would work but only after the battery bank is low. Still trying to find a timer something like a kitchen one that just kills the connection after x time


Thanks for the quick replies!

 

[sailaway78]

I don't get it

In the first place, how can a cell phone charging draw as many amps as a fridge? In the second place, a little cigarette lighter plug can easily charge the cell phone, without using an inverter. And cheap too. Much cheaper than trying to rig up a low voltage cutoff. And thirdly, every inverter I have ever seen, automatically cuts off at around 80% discharge of the battery. Something just don't sound right.

 

[mitiempo]

... every inverter I have ever seen, automatically cuts off at around 80% discharge of the battery. Something just don't sound right.

The inverter does not know what the exact state of the battery is as the voltage is dependent on the amperage draw. Most I have seen will cut out at 10 or 10.5 volts.

 

[Jared1048]

Look up the Sure Start LVD (Low Voltage Disconnect) switches. I think they are still made by Cole Herse. They have them in high amp models and IIRC cut off the voltage at about 12.0-12.2V..

Unfortunately I have to ask why you want to charge a phone via inverter when DC charger are available from Wal*Mart or on-line for about $8.00? A fridge through an inverter can also suck a lot of current at 12V..

The DC amp draw will be roughly 10X what the rated AC amp draw is. So 5A at 120V is 600W that same load on DC through an inverter will look like:

600W / 12V = 50A X inverter inefficiency of 20% = 60A DC to run a 5A/600W rated 120V fridge.. If you can tell us what the fridge is we can give you a more accurate load..

Yes, its very inefficient but we needed a cell phone up and that was our only option at the time.

I'll check the specs tonight but If i remember right it said it drew 2-3Amps @ 120. I havent installed it yet but its a small dorm room refridgerator that I gutted for parts. It was free but Its going to be some work to stuff it in the dungeon with the cooling piece installed at the back of the icechest (looking from inside the cabin). I saw someone else do this in the owners mod's section. I'm still ambivalent on if this is a project i want to continue on.

Cheers,
-Jared

 

[weinie]

Am i missing something here?

 

[Jared1048]

Am i missing something here?

I think i muddied the waters in the post by having too much information and it getting off track. I should of probably left out the information about the cell phone and refridgeration.

My question should of been this simple...

Is there "something" that you can install inline on a power cable with a timer that only allows the connection to stay connected for a set duration? (Like a 15 minute timer you sometimes see in bathrooms that shuts off the lights\fan)

Sorry for the confusion!

 

[Sumner]

I think i muddied the waters in the post by having too much information and it getting off track. I should of probably left out the information about the cell phone and refridgeration.

My question should of been this simple...

Is there "something" that you can install inline on a power cable with a timer that only allows the connection to stay connected for a set duration? (Like a 15 minute timer you sometimes see in bathrooms that shuts off the lights\fan)

Sorry for the confusion!

There still might be some confusion . Will the timer be run by 12 volts? Will the circuit it controls be a 12 volt circuit or 110 (the frig on the inverter).

Here is one that runs on 12 volts and controls up to six 12 volt circuits, but like MS said you have to make sure that the amps falls into the range that it is capable of...

http://www.brazix.com/timer/BRX1224PTS1.asp

Sum

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[mitiempo]

Sum

The only way I can see a 12 volt timer working on the inverter is by connecting or isolating the 12 volt cabling (probably 2/0) to the inverter - way over the amperage of that timer.

An AC timer makes more sense.

 

[Benny17441]

Re: adding timer on inverter power+ to avoid draining batter

The exageration is not that far fetched. A refrigerator will cycle on and off a few tiles in an hour while the charger chugs along continiously. I calculated the draw of a phone charger through an inverter to be around 1.7 ah while that of a cycling dorm refrigerator at 3.5 ah or just about double. It seems the disparity should have been much larger.

 

[Stu Jackson]

Re: adding timer on inverter power+ to avoid draining batter

Could also depends on whether you have the amps settings for 0-8-16-32 settings if your monitor does that. If you have a ammeter, you know for sure.

 

[Sumner]

Sum

The only way I can see a 12 volt timer working on the inverter is by connecting or isolating the 12 volt cabling (probably 2/0) to the inverter - way over the amperage of that timer.

An AC timer makes more sense.

I agree, that is why I asked exactly what voltage the timer was going to be on and what voltage was the circuit to be controlled. What I posted was only for 12 and 12 and the amperage has to be within its limits.

I might try one on our ventilation system for when we are gone from the boat for months along with the low voltage switch I mentioned on my first post, our stuff is all 12 volts as we don't use the inverter on the boat,

Sum

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[Jared1048]

the ah draw on the refridgerator was at 120 and not 12 volts.

I may have tested the inverter wrong but im 95% sure that the 2500 watt inverter draws the same from the batteries no matter what the load is on it.

with that premis in mind i would want to put a timer on the dc side of the inverter to kill the entire inverter by timer. So that would mean a timer that has 2 gauge wire on one side and on the other and be able to withstand 200 amps.

Hopefully its a little more clear?

 

[mitiempo]

You're incorrect. The inverter doesn't draw 250 amps unless it is at maximum output. It will have a small output at idle.

 

[Bill Roosa]

Re: adding timer on inverter power+ to avoid draining batter

The actual math goes like this
AC load power = Wac (W for watts)
DC supply power =Wdc
inverter effency = e
Wac = e x Wdc or rewriting to a more useful form Wdc=Wac/e
so if your microwave is rated at 750 watts (that's power BTW) and the inverter efficiency when supplying 750 watts of AC is 90% (0.9) you will be drawing;
750 / 0.9 = 833 watts from the batteries. Watts is not a very useful term when talking batteries so lets convert to amps
We know that Power = volts times amps and we know the volts and power so we can calculate the amps
P=V X A or rewriting for Amps A = P/V
833/12=69.4 amps draw
To get AH you just need to know how many (probably fractional) hours you ran the microwave. If you ran it for a minute (1/60 hours) your inverter would drain
69,4 X (1/60) = an awesome 1.56 amp hours

The short version is
AH out of the battery = (Wac/e/12) x hours used.

With all that said the inverter can "idle" in one of two modes depending on the model.
it can sleep till it senses a load in which case it draws almost nothing while sleeping
or
it can supply 120 volts at almost no watts in which case it draws somewhere around an amp. If you left it on for 24 hours you would drain the batts by 24 AH.

So in either case the odds of you draining the banks to the point of being dead are pretty unlikely.