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conway400
08-22-2007, 03:29 PM
Question for an expert (or semi-expert will do): If I have a 100amp/hr battery, I assume (under ideal conditions) that I can pull 100amps on a full charge for one hour before it dies. I also think that if I am using 1200watts/12v that means a 100amp load. Correct?

If the above is true - I am on the right path. More important question: If I am using an inverter to draw my power and it steps things up to 1200watts from the battery, does the above all still apply?

Thanks in advance!

(BTW - just wanting to power a boat lift at about 1000watts - several times over the weekend on one charge - takes about 2 to 3 minutes per raise.)

Leroy
08-22-2007, 04:03 PM
Battery specs are really tricky.

Normally batteries have a short burst rating, cold cranking amps (CCA) and a amp-hr rating over 20 hour period (a battery day).

So your 100 amp-hr rating is good for 5 amps for 20 hours. Reality check, normally 3-6Amp pull will kill a good battery in just under a day.

This motor will be pulling current as though it were starting an engine and we know how long batteries last and that is in minutes.

The inverter should work if the battery is big enough, it will lose some efficiency in the conversion. I doubt those specs are big enough for a 1200W motor.

For Reference:


Amp-Hour battery rating: This is a common battery rating of batteries. Amp-hour rating of battery capacity is calculated by multiplying the current (in amperes) by time (in hours) the current is drawn. Amp-hour battery rating is commonly used on sealed lead acid batteries used in UPS systems, emergency lights and camcorders.
For example: A battery which delivers 2 amperes for 20 hours would have a 40 amp-hour battery rating (2 * 20= 40).

Cold Cranking Amperage battery rating: CCA is the discharge load in amps which a battery can sustain for 30 seconds at 0 degrees F. and not fall below 1.2 volts per cell (7.2V on 12V battery). This battery rating measures a burst of energy that a car needs to start on a cold morning. This rating is used mainly for rating batteries for engine starting capacity and does not apply to NiCad batteries, NiMH batteries or Alkaline batteries.

Reserve capacity battery rating: RC is the number of minutes a new, fully charged battery at 80 degrees F will sustain a discharge load of 25 ahps to a cut-off voltage of 1.75 volts per cell (10.5V on 12V battery). This battery rating measures more of a continuous load on the battery.

conway400
08-22-2007, 04:19 PM
Thanks for the info. It is indeed very confusing. Your info on apm-hours is very helpful.

I have used this inverter (just a bigger version of any inverter you would use in a cigarette lighter, but wired directly to the battery) to raise the lift several times. But that was my old boat and the boat was run between times (thus recharging the battery). The lift motor is just a 110v AC electric air compressor.

I am trying to figure out how many times I can safely lift the boat if I bring down a fully charged battery for the weekend, then take it back up to the house to recharge it.

The easiest and foolproof way to know is to try it, but I don't want to throw money away buying a battery and parts for nothing.

Leroy
08-22-2007, 04:32 PM
Keep in mind every time you kill the battery it loses like 50% of it's capacity.

How many watts is the electric air compressor motor? How long to lift and drop? If for example it is 240 watts then your current draw is 20 amps and you may be good for several times depending on the lift/drop times.

conway400
08-22-2007, 04:34 PM
Thanks! - I'll get all the motor and inverter specs this weekend. :)

T Scott
08-22-2007, 04:36 PM
Question for an expert (or semi-expert will do): If I have a 100amp/hr battery, I assume (under ideal conditions) that I can pull 100amps on a full charge for one hour before it dies. I also think that if I am using 1200watts/12v that means a 100amp load. Correct?

If the above is true - I am on the right path. More important question: If I am using an inverter to draw my power and it steps things up to 1200watts from the battery, does the above all still apply?

Thanks in advance!

(BTW - just wanting to power a boat lift at about 1000watts - several times over the weekend on one charge - takes about 2 to 3 minutes per raise.)

Have you considered a solar trickle charger to keep the battery topped off?

conway400
08-23-2007, 03:14 PM
Ultimately, that is exactly where I was headed. I could get all that set up for a modest investment and be done with it. leave and not haul anything back and forth.

However, now I am finding some lesser know brand name generators for the $150 dollar range (portable and small) in the 1250watt area that would work great. Still studying...

JimN
08-23-2007, 03:51 PM
The invertor won't step it up to 1200W, it steps it up to whatever the AC voltage is and the limit for its output is 1200W. A battery with a full charge will do much more than 1200W for a short period of time. If you dump a lot of current in a short period, it may not last long, but it'll do it. An invertor will probably burn the windings if you overtax it, unless it's protected.

conway400
08-23-2007, 04:04 PM
Burn the windins of what? The aircompressor motor?

How do I tell what watts it is pulling? It is just a 110 volt motor I believe.

Leroy
08-23-2007, 05:51 PM
The motor will have an aluminum tag on it that tells the watts used.

When the battery gets weaker the inverter will not put out 110v, but something less most likely, 80-90 volts and at the lower voltages motors slow down or quit running and the energy normally converted into spinning energy now burns up the windings in the motor.

pilot02
08-23-2007, 05:58 PM
I'm not sure of the exact setup but at Lake Francis (waterskiatlanta.com) there is a battery to power the lifts and a solar charger is hooked up to that to recharge it. Could be using 12v lift motors though.

JimN
08-23-2007, 07:21 PM
conway400- According to the theory, for a device to produce the power it was designed for, P(Power) = I(Current) x E(Voltage). Technically, the term 'Volt-Amps' should be used, not power, in a case like this. If P remains constant at 1000W and the voltage drops, the current has to increase. At a nominal 120VA, 1000W = X(120V), or 8.33A. If E drops to 80VAC, I increases to 12.5A. More likely, the current will increase and pop a breaker. If the compressor is on an extension cord, it can pop a breaker with no load.

Why not buy a 12Vdc motor and the hardware for a regular lift? Someone must have one on ebay, or someplace like that.

conway400
08-24-2007, 11:08 AM
Thanks for all the info. I will check specs tonight on the motor when I go up. I don't think I need a DC motor. My issue is with the easiest way to consistantly power the lift. The corp will not allow the dock to be powered.

My final solution will likely be to wire two batteries together (so I can power more stuff like maybe some lights for little while), the inverter, and a solar trickle battery charger (with regulator). I just don't want to go to that expense or trouble this late in the year. And whatever I do has to faily safe and theft proof.

So - the best immediate answer was for me to try to use a battery carried down and charge it at home after the weekend. So I was trying to understand if it would last long enough to be worth the trouble.

The other option, which would work forever but I would have to carry something each time, is to bring a small, portable generator down. I am now trying to understand how small will work. No name brand ones in the 1000watt range can be found for around $150 online. :)

Leroy
08-24-2007, 12:00 PM
Why not use the battery on the boat? You could even have a special connector.

TX.X-30 fan
08-24-2007, 02:30 PM
You could use a solar powered gate opener, with some modifications. My opener is supposed to open and close the gate 15 times a day. I never use it more than a few though. Same as a boat lift few times a day would be plenty.

Leroy
08-24-2007, 02:45 PM
Dependable, reliable, safe and healthy.....

The Human Power Generator System (http://www.windstreampower.com/humanpower/hpginfo.html) is small, portable, and dependable - perfect for emergencies, power failures, remote locations, and off-grid applications. It can be pedaled or cranked by hand to charge 12 volt batteries and run small appliances. Incorporate it into your existing 12 or 24 volt system or simply plug your 120 volt appliance into the Human Power Generator System outlet and start pedaling. It's as easy to operate as an ordinary bicycle.
The Human Power Generator System comes equipped with the Human Power Generator (pictured at left) and a stand-alone Power Box which includes: storage battery, 200 watt inverter (with 300 watt peak power), LED battery voltage readout, connection cables, and a 120 volt outlet to turn your calories into useful power.

conway400
08-24-2007, 03:05 PM
Oh man! I could make my boys earn that gas money!

TX.X-30 fan
08-24-2007, 03:10 PM
[QUOTE=Leroy]Dependable, reliable, safe and healthy.....




Where do you sit. :confused:


My idea was green too!! :mad: 8p

Leroy
08-24-2007, 03:40 PM
Hmmmm, welll, uhhh,,,,.....

Unicycle strategy!

Guess you could pull any chair up next to it.


[quote=Leroy]Dependable, reliable, safe and healthy.....




Where do you sit. :confused:


My idea was green too!! :mad: 8p