How long will the inverter run on batteries?

[jk510]

Something to keep in mind is that the stated current draw is only for when the fridge is cooling down. Once it reaches temp the power usage will drop way down until it's time to go into the cooling cycle again.

[WolfWhistle]

Originally Posted by Mikele

About 10 minutes..But seriously, We have a REBH371 with the whirpool fridge. The inverter is 1000w with 2000 surge, and we have 1 optima blue top along with a 80watt solar panel. When hermine came through we lost power for 5 days and were forced to dry camp.(we fulltime) I thought ok im good to go..Wrong. The fridge killed the battery in about an hour. The biggest issue i had was the inverter, it turns off at 11.5v. Which takes no time to get down to. I called the manufacture of the inverter to see it was broke and that was the reply i got. I dont know if all inveters are made this way but it seemed odd to me. However, While towing ive never had issue with it cutting off, but otherwise i had a time with ours.

My inverter is programmable including the point (voltage) it stops inverting... or cuts off. It came out of the box set to 10 vdc. I can't afford to kill my batteries, so I set it for around 11 vdc, but probably should be closer to 12.0 vdc... such as the 11.5 you have. I would look at the wiring you have to the inverter (dc side) and be sure it is adequate. I think you have a couple of issues that would lead to a res fridge killing a battery that quickly. First, it wasn't fully charged at the beginning of that hour and, even if it was, you need more than one battery if you want to run the fridge for even one full day. Then you need to have a way to put back into the batteries, what you take out.
WW

[camaraderie]

Originally Posted by WolfWhistle

My inverter is programmable including the point (voltage) it stops inverting... or cuts off. It came out of the box set to 10 vdc. I can't afford to kill my batteries, so I set it for around 11 vdc, but probably should be closer to 12.0 vdc... such as the 11.5 you have. I would look at the wiring you have to the inverter (dc side) and be sure it is adequate. I think you have a couple of issues that would lead to a res fridge killing a battery that quickly. First, it wasn't fully charged at the beginning of that hour and, even if it was, you need more than one battery if you want to run the fridge for even one full day. Then you need to have a way to put back into the batteries, what you take out.
WW

Look at this chart and understand that whenever you move below the GREEN on a static battery....you are damaging your battery and cutting its' life GREATLY.
Anything 11.5 volts or less repeated just a few times will cause damage. If you can't afford to kill your batteries you need MORE of them so you never go below 12.2V and maximize your battery life. Going below 50% to 30% causes about 40% cycle life loss...Going to 11.5V will cause over a 60% loss.
A TRUE battery monitor like the Victron will TELL you how many amp hours you normally draw in a day (as well as lots of other useful stuff) and you then need to purchase TRUE deep cycle batteries with DOUBLE that amount of amp hours in order to remain above 50% battery power ASUUMING that you recharge each day. Otherwise...double your batteries for each additional day without charging. "Pay me now or pay more later. "

BTW...I think it was the original poster who said he had Optimas....THEY do not make a deep cycle battery so you're in trouble with cycle life from day 1.

[camaraderie]

One other thing worth mentioning is that if you have say a 100 amp hour deep cycle battery....that is a 20 hour rating ...so you can run 5 DC amps for 20 hours.
Now if you want to run 10 amps....you might think you can run for 10 hours at 10 amps...but it ain't so. Peukerts constant REDUCES time ...the greater your current draw is. One would typically get around 85% of the expected time...at double the rated current..and it gets worse...the greater the current being drawn. So regardless of the battery rating...if you've got big stuff running off DC OR being inverted from DC...you have to make some significant allowances...which a good battery monitor will also quantify for you since they work off Mr. Peukerts constant formula.

[WolfWhistle]

camaraderie, I have all those charts and understand how to manage batteries, but thank you. You might have missed that the conversation shifted to "inverter cut off". You might have missed my other post.

This setting isn't considering battery longevity, rather to prevent damage.

For example, if you were on inverter to run a CPAP, you might not want it to cut off at 12.0vdc in the middle of the night leaving you without an important function. So, for "cut off" and to prevent damage that number should be lower. In some cases, and at some times, you might NEED to drain the batteries below the ideal percentage of discharge.

WW

[camaraderie]

Wolf...yup..I hadn't read up above in a while and was just responding to the immediate post that popped up in my mailbox! I would still set my cutoff a lot higher than 11.5 non static. The situation with CPAP of course is serious medical so if you want to be both safe and avoid damage to the batteries and you're constantly getting to the low point cutoff...then you need another batt of course. If you can't do that , thn the only solution is to set the LPC lower, understandinf you are giving up battery cycles for safety. Sorry for the confusion on my part!

[WolfWhistle]

Originally Posted by camaraderie

Wolf...yup..I hadn't read up above in a while and was just responding to the immediate post that popped up in my mailbox! I would still set my cutoff a lot higher than 11.5 non static. The situation with CPAP of course is serious medical so if you want to be both safe and avoid damage to the batteries and you're constantly getting to the low point cutoff...then you need another batt of course. If you can't do that , thn the only solution is to set the LPC lower, understandinf you are giving up battery cycles for safety. Sorry for the confusion on my part!

Thanks C, I completely agree that if cut off is reached other than on rare occasions, something needs to be fixed, whether than is more batteries; more or better charging. On my Inverter there is also options for AGS (auto gen start), which could come into play based on battery voltage. I don't have such a genset, but is a nice feature for those that have one.
WW

[ScottBrownstein]

This is not a trivial issue. While the charts show that a 50% discharge on a 12 volt battery is reached at around 12.1 volts, THAT IS FOR A BATTERY THAT IS IN STATIC CONDITION. This means that it has been sitting for at least 6 to 12 hours with neither charge nor discharge. An inverter low cutoff occurs when the battery is being discharged by the inverter, often drawing significant current depending on the 120 volt load at the time. As such, 11.5 is not necessarily drawing the battery below 50% anyway, as I bet if you let the battery set after the shutdown you will find it back to nearly 12.1.

[WolfWhistle]

Originally Posted by ScottBrownstein

This is not a trivial issue. While the charts show that a 50% discharge on a 12 volt battery is reached at around 12.1 volts, THAT IS FOR A BATTERY THAT IS IN STATIC CONDITION. This means that it has been sitting for at least 6 to 12 hours with neither charge nor discharge. An inverter low cutoff occurs when the battery is being discharged by the inverter, often drawing significant current depending on the 120 volt load at the time. As such, 11.5 is not necessarily drawing the battery below 50% anyway, as I bet if you let the battery set after the shutdown you will find it back to nearly 12.1.

I get what your saying Mr. B, the voltage in question is under load. Lets say I was powering "things" that were pulling 100+ amps DC via the inverter; and at that point in time, the loaded voltage reading might be in the high 11s to low 12s. It (the 10 volt default) seemed low to me even considering what I know. So, you are saying that 10 volt LBCO is what I should have stayed with?
WW