Inverter size

[escavader]

I agree. Those safety cutoffs Vs are set too high for high drain conditions. The idea for the safety cuttoff is to assure that you never run one of the cells in the 12 V batt completely dead while the others are still sourcing current. If this happens the strong cells will forcecurrent to continue flowing thru the dead cell and charge it backwards. This is very harmful. For that reason safety cutoff is always set at at least nominal bat V minus one cell. They have gone overboard in their protection except for low drain situations. A battery drained slowly, say 5 or 10 amps for a car batt, is pretty dead at 11.5 - which is about what they seem to be setting it at these days. Doesnt let you get a decent percent of discharge at hi drain tho. 10 or 10.5V cutoff would be gould in my opinion. That would let you pull 100A until the battery was about 50%.
larry

LARRY,
Interesting,but I have a question,that confuses me.If there is a danger of harming a deep cell battery from draining it to nothing[which is why for an inverter safety shutoff],then why does an electric trolling motor on a boat ,which drains it to nothing not hurt a battery?It was always my assumption a deep cell battery was designed to be drained to nothing,rather than a car battery,that would be ruined in doing so.
If the answer is that it will not harm a deep cell battery heres a question.Iam running a small refridgerator mostly,is there a way to do away with this feature in my inverter,so i could get all the juice available from my batterys
SORRY NOT TRYING TO STEAL THE THREAD HERE but i have wondered about this stuff myself.
ALAN

 

[patrick_g]

Comments and observations: Remember that the AH (Amp Hour) rating is based on a 20 hour discharge. So, for a 100 Ah batt you get 5 amps for 20 hours. You absolutely CAN NOT get 20 amps for 5 hours due to reason posted previously. Taking out the power quicker reduces the total power you will get. 5 amps DC at 12 volts will only give you 1/2 of an amp at 120 VAC (will run a 60 Watt light bulb WITH 100% inverter efficiency.)

100 Ah starting batts will give you a couple hundred amps for a little while or will power an inverter with 15 amps 120 VAC output for just a very short period of time, long enough to make just a few Skill saw cuts.

6 volt golf cart batts (2 in series for 12 VDC) are about the best bargain. Trojan is a good brand of batteries too. One about the size of a pickup starting battery is 220 AH. Batts in series you add the voltage. The AH (if both batts are same rating) stays the same. This is about the smallest batt bank that could give good service running an inverter used intermittently to give about 10-15 amps to run one tool at a time. (good skill saw draws 12-15 amps)

Many powered hand tools are actually AC/DC. Do the math, maybe 10 little batts in series for use and parallel to charge would be cheaper than an inverter and would certainly be more efficient too.

I bought a 13.5KW surge electric start genny at Lowe's (refurbished cust return) for $400. My 6 Kw Coleman cost $500 new at Sam's and will run just about any one tool at a time including my MIG and even the Lincoln tombstone at lower settings.

There are Gen heads setup to be belt driven and can be adapted to a tractor PTO super easily. 10Kw peak, 7200 continuous, Harbor Freight $300 This would be a 600 amp draw with a 100% efficient inverter and require about a dozen large automotive batts in parallel or 6 golf cart batts in series parallel and then the generator will run for hours and hoiurs and the batts and inverter won't.

5500 Watts cont 6500 surge with gas engine for $570 (Harbor Freight)

Unless you get a spectacular deal on batteries and an inverter it is tough to beat an engine driven generator, even for brief work sessions within the very limited capability of many battery and inverter setups.

I too am a ham radio type (and used to make a living as an electronic design engineer) and have used inverters lots of times. They often are NOT the system of choice.

Pat

 

[slowrev]

This might be too bulky, but here is a thought. Buy 2 6V Golf Cart batteries rated at 220 Ah - 250 Ah and a 1000W - 1500W Inverter and a Battery Isolator. Hook up batteries for 12V. Make a container and mount either permanently or removable on the back of the tractor. This should give lots of power and capacity until back to home for a recharge. The Isolator would give some recharge capability from the tractor charging system. Probable cost - less than $300. the GC battery is much more suitable for discharge / recharge than 12V cranking battery.

That is what I am rigging up for short term emegency power at home Cinder.
The 2 golf cart batteries are only $120 total at sams. $159 for a 2000w inverter at HF , I already have a couple of 700 watt inverters.
I also have about 100ft of heavy duty welder cable to run from the inverters to the batteries.
I have a 130 amp alternator hooked up to an 11hp briggs for charging. I also use the briggs Alt rig to charge dead batteries on various equipment that is not near an AC outlet.
And I will rig a 10 amp float charger to slow recharge the batteries.

I also have a generator for longer term problems.

 

[SPYDERLK]

Alan, no lead acid battery is unharmed by deep discharge. Deep discharge batteries are just harmed less. It is not good to allow the terminal voltage of a 12V batt to drop below 10V under load. Such indication is either due to excessively high drain or a badly discharged condition. Starting a car in cold weather will often pull the battery to this level or even a little below due to high starter demand aggravated by the degraded performance of the battery at low T. However, the battery is immediately recharged and harm from the high drain is extremely slight. If immediate recharge is not done a deep discharge would have superior service life, however with prompt restoration of charge I find high cranking amp car batteries perform better and last longer with drains inherent in cranking and inverter use. It is frustrating for an inverter to cut out at so high a minimum. Given a circuit diagram I imagine a EE guru could figure out how to change the safety cutoff level. I would never want to go below the 10.5V range tho. A healthy battery under low drain is real near dead at that voltage. A charged healthy battery under high drain that drops its output to below 10.5 is at an extreme that will cause damage if sustained more than 10 or 20 seconds.

Dont run your deep discharge batteries all the way down unless the situation dictates. Theyll last longer if kept at a higher charge level. Just be sure to check the fluid level more often.
larry

 

[Soundguy]

Did you completely ignore my post on this?!?!?!?

Look.. you need to go to a community college and take ac/dc electronics, 1st year course.. then you may understand this a little better.

There is NO WAY to suck yer 12v battery down to 0.0 volts using an inverter.

What don't you understand about voltage / current / power relationships. You are getting a 10:1 conversion ratio not taking into account the probable 10% inefficience in the inverter. As voltage ( electromotive force.. or potential ) on the battery drops.. the current must go up in order to maintain the power output demand because the load has not changed. As potential drops.. the ability for current capacity drops..

E=IR
P=IE

No magic here.. just math..

Also.. as has been said.. a car battery setting at lower than 12v is already considerbly 'drained' when looking at capacity...

Soundguy

,is there a way to do away with this feature in my inverter,so i could get all the juice available from my batterys
SORRY NOT TRYING TO STEAL THE THREAD HERE but i have wondered about this stuff myself.
ALAN

 

[patrick_g]

Originally Posted by escavader
,is there a way to do away with this feature in my inverter,so i could get all the juice available from my batterys
SORRY NOT TRYING TO STEAL THE THREAD HERE but i have wondered about this stuff myself.
ALAN

Yes, there is a way to use batteries all the way down while maintaining full output voltage and current output from an inverter. It takes a different sort of power conversion circuit from the typical off the shelf inverter and the abuse done to lead acid batteries powering it is brutal and essentially ruins the batteries in short order, usually in just a very few cycles (frequently the first time.) This IS NOT what most folks would want, a one shot operation per set of batteries but in certain applications where power density is much more of a concern than the cost of the batteries for probably just ONE use. Other types of batteries are often but not always used in these Kamakazi type circuits.

It is not a simple thing such as disabling the low voltage cut out. The majority of the circuitry is designed quite differently in the KAMIKAZI application. If you disable the low voltage cutout in a STANDARD type inverter you will get a little more out of the inverter but not enough to warrant ruining costly batteries. From the time the batteries reach about 10.5 to 11 volts till they are exhausted to the point that even a Kamakazi circuit can't wring anymore use out of them doesn't give you a whole lot more Watt Hours of output before the output is not sustainable and goes below any reasonable minimum AC voltage. Most stuff hates running on less than 90VAC so not only do you ruin your batteries you also can ruin power tools.

Pat

 

[Egon]

E=IR
P=IE

In the simple world this may apply but get into the real world and it's only an indication of what may happen.

 

[escavader]

Did you completely ignore my post on this?!?!?!?

Look.. you need to go to a community college and take ac/dc electronics, 1st year course.. then you may understand this a little better.

There is NO WAY to suck yer 12v battery down to 0.0 volts using an inverter.

What don't you understand about voltage / current / power relationships. You are getting a 10:1 conversion ratio not taking into account the probable 10% inefficience in the inverter. As voltage ( electromotive force.. or potential ) on the battery drops.. the current must go up in order to maintain the power output demand because the load has not changed. As potential drops.. the ability for current capacity drops..

E=IR
P=IE

No magic here.. just math..

Also.. as has been said.. a car battery setting at lower than 12v is already considerbly 'drained' when looking at capacity...

Soundguy

TAKE IT EASY I didnt ignore you.Im confused ,if i knew the answer,i wouldnt have asked the question.I asked why you could run a deepcell battery to nothing on a boatmotor[which is 12 volt]NO INVERTER and you dont hurt the battery,but you would ruin a car batteryand why cant you run it down to nothing with an inverter.If I wanted to go to college i would,but I dont need to,i got nice people here on TBN who answer my questions,sometimes even without barking.Thanks for the answers guys,im afraid to ask any more questions
ALAN

 

[schmism]

TAKE IT EASY I didnt ignore you.Im confused ,if i knew the answer,i wouldnt have asked the question.I asked why you could run a deepcell battery to nothing on a boatmotor[which is 12 volt]NO INVERTER and you dont hurt the battery,but you would ruin a car batteryand why cant you run it down to nothing with an inverter

think of it this way, the trolling motor is just like a constant watt load. with speed of the motor directional proprtional to the voltage of the battery.

so as you drain the battery the motor spins slower and slower as the voltage drops off (W=Volts*Amps)

an inverter has more complicated ciruitry involoved. It trys to output the same wattage for a giving V*A.... as the voltage drops current draw has to go up to maintain the same W. But its been my experience that as V(in) drops V(out) drops keeping A roughly the same but your tool on the other end isnt very happy, and then the inverter goes into low voltage protect to keep the output side of things happy.


back on topic


In my world the use of a medium size inverter for small infrequent use FAR out weighs the usefullness of a cheep motor driven geny or PTO driven version.

from pulling the tractor up and parking it next to the bon fire (with attached inverter) to run the blender for fresh maragrits or a boom box.. to charging the cell phone while brush hogging, to recharging the cordless drill battery packs while working 100% cordless project (trim saws, drills, recip saws etc)

need to plug 100 3" holes in my yard for bulbs, would kill the cordless drill in about 10 holes, but the milwalkee hole shooter has to be used for less than 15 min to get the job done....

Ive found myself cussing my current 450w inverter (for cell phone charger/GPS power in the car) while trying to use the soldering iron to do wiring repair on the truck 300' from the garage, or the dremel.

ya i COULD walk back to the house, find the keys, fire up the truck, jocky it around to get close to the garage for a normal extension cord, but by the time ive done all that i could have had my issue fixed already with a simple portable power solution.

 

[patrick_g]

Alan, I gave you a NO BARK answer. It may not be the answer you want but it is the way the things work. Running a deep cycle batt all the way down does shorten the batt life (fewer charge/discharge cycles.) Just because you don't get a catastrophic failure the first time every time doesn't make it a good thing for the batt. The penalty with the electric troling motor is it just goes slower and slower till it won't go. The Inverter is "smart" enough to shut down when it can't get enough out of the batt to give you the required output. Without that feature your output voltage would get lower and lower once the batt went below a required voltage lavel under load. This is NOT GOOD for power tools. Not only an inconvenience to have tools run slower but "starvation" can burn out tools. Too many, too long, or too light duty of extension cords will help burn out a tool. Low inverter output does the same.

Pat