| Author | Message | ||
| Doyle Gaither (Texasborderdude)
Registered Member Username: Texasborderdude Post Number: 85 Registered: 3-2007 Posted From: 75.205.239.30 Rating: |
Okay there's been lots of discussion about batteries, inverters, etc. and probably always will... it's such an integral part of the bus thing especially for fulltimers. I just replaced 8 each 6v. Interstate house batteries with a 230 amp rating, arranged in 2 banks delivering 12v to my Trace 2500 inverter. So here are the questions... If my volt meter shows 13+ volts when full charged (12.6 is technically full charge, I'm told) and if I consume 200 amps (1/4th the capacity) at 1500 watts over 13 hours and recharge by shore power, genset or alterator..... 1)Isn't this pretty much the "theoretical optimum" performance for this setup? and 2) Is there a downside to leaving the inverter on all the time to charge when on shore power, genset and alternator; and act as a ups if power fails or when dry camping? Ps. Shouldn't this setup operate one roof air? Thanks, dg (Message edited by TexasBorderDude on November 02, 2007) | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 282 Registered: 8-2006 Posted From: 207.231.75.253 Rating: |
TBD, Your question is asking about apples, oranges, and maybe a yellow citrus fruit? Anyhow, lets make fruit salad! Eight six volt batteries rated 230 amp hours each will provide 920 amp hours of theoretical 12 VDC when connected in four series-parallel groups. In reality, a good inverter will shut off for low voltage long before that number is reached. Watts are amps times volts, so "200 amps" at 120V is a LOT of watts, while "200 amps" at 12V is only 10% of that amount. So, to answer your questions, one 13,500BTU roof air rated 10 SEER will consume 1,350 watts/hour. At 120 VAC, this is about 11.25 amps. If your inverter's efficiency was 100%, which it isn't, you would draw 112.5 amps of 12VDC from your batts, per hour. Reality is an inverter efficiency in the low 90s, so your draw will be in the 125-135 amp range. My guess is that your batts would provide about four + hours of one A/C operation per charge. Charged batteries last much longer than discharged ones, so definitely leave them on charge at all times. John MC9 made an excellent post on battery life/use a month or so ago, it is well worth the effort to find it in the archives, and use your batteries accordingly. HTH, George | ||
| Doyle Gaither (Texasborderdude)
Registered Member Username: Texasborderdude Post Number: 86 Registered: 3-2007 Posted From: 75.204.102.59 Rating: N/A |
Excellent clarification! Just gave ya a vote... :-) That's what I wanted to know... soooo using the 920 amp hours and wishing not to draw down more than 25% of full charge... that's about 2 hours for 1,500 watts at 120v allowing for inverter inefficency, correct? That's the kind of benchmark I wanted so I could judge actual performance. | ||
| Jerry Liebler (Jerry_liebler)
Registered Member Username: Jerry_liebler Post Number: 293 Registered: 3-2005 Posted From: 67.140.173.217 Rating: N/A |
Doyle, Agreed you have effectively an 920 Amp hour battery AT THE 20 HOUR DISCHARGE RATE or 46 amps. Or you can use a 500 watt load on the output of the inverter for 10 hours and use 1/2 the battery capacity. However if your load is greater than 500 watts you'll get LESS energy back from the battery. The effect is called Peukert's effect and it's different for different battery designs. It is predictable but it involves complicted mathematical formulas. Here is an example,using my batteries, of what may happen, each of the following loads and times will take half the charge from a battery about like yours: 50 watts for 140 hours--------------7000wh 500 watts for 10 hours---------------5000wh 1000 watts about 4 hours 30 minutes--4500wh 2000 watts about 2 hours ------------4000wh There is no good reason to only use 25 % of your battery, You'll get very little extra life over cycles of 50 % of capacity, the key is don't let it sit uncharged,recharge promptly. Regards Jerry 4107 1120 | ||
| Doyle Gaither (Texasborderdude)
Registered Member Username: Texasborderdude Post Number: 87 Registered: 3-2007 Posted From: 75.205.29.176 Rating: N/A |
Okay, just to be sure I have it straight in my head, are the wattage and times above at 120 volts through the inverter? All makes sense and is consistent with George's estimate of 4 hours or so on a 1350 watt a/c. Guess it's kinda like a debit increases an asset or expense but decreases a liability... once you get it; you get it! Thanks, dg | ||
| Jerry Liebler (Jerry_liebler)
Registered Member Username: Jerry_liebler Post Number: 294 Registered: 3-2005 Posted From: 67.140.173.217 Rating: N/A |
Doyle, Agreed you have effectively an 920 Amp hour battery AT THE 20 HOUR DISCHARGE RATE or 46 amps. Or you can use a 500 watt load on the output of the inverter for 10 hours and use 1/2 the battery capacity. However if your load is greater than 500 watts you'll get LESS energy back from the battery. The effect is called Peukert's effect and it's different for different battery designs. It is predictable but it involves complicted mathematical formulas. Here is an example,using my batteries, of what may happen, each of the following loads and times will take half the charge from a battery about like yours: 50 watts for 140 hours--------------7000wh 500 watts for 10 hours---------------5000wh 1000 watts about 4 hours 30 minutes--4500wh 2000 watts about 2 hours ------------4000wh There is no good reason to only use 25 % of your battery, You'll get very little extra life over cycles of 50 % of capacity, the key is don't let it sit uncharged,recharge promptly. Regards Jerry 4107 1120 | ||
| George M. Todd (George_mc6)
Registered Member Username: George_mc6 Post Number: 283 Registered: 8-2006 Posted From: 207.231.75.253 Rating: N/A |
Doyle, Thanks for the vote. Please remember that Watts are Amps X Volts. So an appliance using 1350 Watts will use 11.25 Amps at 120 Volts, or 112.5 Amps at 12 Volts. A quality inverter such as yours will probably have an efficiency rating of about 95%, but a difference of 4-6% will have little effect on the end result. The bottom line of this is that the watts used is what really matters, not so much the voltage. If you look carefully at Jerry's post, you will see that batteries give out more total current when discharged slowly, rather than quickly. I know Jerry to be well qualified to speak electrically, and you will note that all of us reccommend keeping batteries charged when not being used, as the best way of extending battery life. Go out and enjoy it, George | ||
| niles steckbauer (Niles500)
Registered Member Username: Niles500 Post Number: 798 Registered: 11-2004 Posted From: 72.91.168.92 Rating: N/A |
*** No argument with the math so far - but as George stated "batteries give out more total current when discharged slowly" - so the higher the amp draw (A/C vs. other loads) the less standby power is available or: "if a battery is subject to a fast discharge (such as starting a car, which is a draw of some 600 amps) for a few minutes, it will appear to go dead. Most likely it has only lost its interface charge; after a wait of a few minutes it should appear to be operative. On the other hand, if a battery is subject to a slow discharge (such as leaving the car lights on, which is a draw of some 6 amps), then when the battery appears to be dead it likely has been completely discharged" HTH | ||
| Glenn Williams (Glenn)
Registered Member Username: Glenn Post Number: 99 Registered: 6-2006 Posted From: 216.163.56.136 Rating: N/A |
A question I did not see answered was whether or not to leave the inverter on while on shore power, or on genset as back-up. In a similar question, during storage times, do you leave the inverter on (bus plugged into 110)to monitor the batteries? I just bought an sw4024 10 minutes ago so very much new to this. | ||
| Jerry Liebler (Jerry_liebler)
Registered Member Username: Jerry_liebler Post Number: 295 Registered: 3-2005 Posted From: 67.140.173.217 Rating: |
Glenn, Congratulations on buying the 'ultimate ' inverter. You absolutely should keep the inverter on when power from generator or shore is available, because it is a very good battery charger. You will have to learn to program the inverter (not all that hard). Another benefit of leaving this model inverter on while connected to a shore cord is that you can program (limit to 14 amps for example) the capacity of the shore cord and still start or run much larger loads than the shore cord alone could. Regards Jerry 4107 1120 | ||
| Don Evans (Doninwa)
Registered Member Username: Doninwa Post Number: 86 Registered: 1-2007 Posted From: 66.45.165.58 Rating: N/A |
I just noticed on Xantrex's site that they list the SW4024MC2 as discontinued. http://www.xantrex.com/web/id/44/p/129/pt/10/product.asp Don 4107 | ||
| Glenn Williams (Glenn)
Registered Member Username: Glenn Post Number: 100 Registered: 6-2006 Posted From: 216.163.57.212 Rating: N/A |
Wow Don, That's not good. They say the Prosine 3.0 is a replacement! I'll post the item number from my auction on e-bay here. This seller had 2 more of the units brand new. item no.190169338327 | ||
| Sean Welsh (Sean)
Registered Member Username: Sean Post Number: 687 Registered: 1-2003 Posted From: 67.142.130.27 Rating: N/A |
Just FYI, the 2512MC is still available, and the SW4024 (not the MC2 model) is available again after a brief absence from Xantrex's product line. The difference between the SW4024-MC2 and the regular SW4024 is less than you might imagine -- see my extensive write-up at http://ourodyssey.us/bus-e-trace.html The Prosine units, as well as the higher-end RV models, while more modern and compact than the SW series, lack the load-support capability of the SW series that derives from their grid-tie ancestry. For this reason, if I were to be doing this again today, I would stick with the SW4024, even without the MC2 features. Also, FWIW, there is probably quite a bit of MC2 product still in the channel, so you will likely be able to find these units, still brand new, for quite some time to come. -Sean http://OurOdyssey.BlogSpot.com |
