Two 6 volt batteries or two 12 volt batteries ??

SoundGuy wrote:

otrfun wrote:
Before this thread, I never gave alarm and shutdown voltage a lot of thought. Guess we lucked out with an inverter that supposedly shutsdown at 10.0 volts. Our previous inverter shutdown at 10.5 volts. Didn't realize some inverters shutdown at 11.0 volts or higher. Depending on system capability (batteries, cable length/size, etc.), a 1 volt difference like this could potentially be a huge deal in some dry camping situations. Going forward, we're definitely going to be looking much closer at alarm/shutdown voltage specs.

We don't dry camp often so I wasn't willing to invest a lot of $$$ in an inverter but decided to add one to our trailer a few years ago when found I could buy a "good enough" 1000 watt PSW for $200 Cdn at Canadian Tire. It's the only PSW inverter they sell and in reality is a Chinese manufactured NPower inverter, hardly high quality but does do what I want. It's low voltage alarm threshold is spec'd at 11.0 volts, +/- 0.3 volts, meaning it could alarm at even 11.3 volts - in reality I've found it starts to be unhappy around 11.5 volts. Both of the heavy loads I want it to run - toaster and coffee maker - are resistive loads, so excessive surge from an inductive load isn't an issue for me. If it were that would be a reason for a much better quality inverter capable of a much lower alarm threshold. Further to this though, if this inverter does shut down due to low incoming source voltage it's spec'd to not restart unless that incoming voltage rises to 11.6 volts, +/- 0.3 volts, meaning it might have to be as high as 11.9 volts before it would be willing to restart ... yet another reason a higher quality inverter that would restart at a lower voltage might for some be a better choice. No question about it, voltage drop and inverter low voltage threshold are just as important as which battery (or batteries) to use to power that inverter.

You would think higher cost inverters would have the lowest alarm/shutdown voltage specs. For our last project we simply purchased the cheapest 1000 watt PSW inverter we could find on Amazon, with very little regard for any of the specs, and lucked out with this unit that had a claimed 10.0 volt shutdown voltage. Price just went up. It was $139 just last month. Aims sells the same exact unit (in blue with an Aims sticker) for $30-$40 more. We've had it down to 10.5 volts with no alarm or shutdown---output voltage was still stable at 117 vac with a 700 watt load. Can't verify waveform distortion---but it does power a lot of sensitive stuff that won't operate with a MSW inverter. Good enough for this particular project. BTW, parasitic current is .5 - .7 amps. Not great, but for the money and wattage not bad.

SoundGuy wrote:
Not true, if one of two 6 volt trailer batteries fails one can't load support the remaining 6 volt with a truck's 12 volt electrical system.

Well of course, but it can support the trailer's 12v needs.

mike-s wrote:
I can't recall hearing of any sudden failures of deep cycle batteries, and it's never happened to me - they die a slow death.

x2. Nobody seems to have this level of fear for their car battery.

SoundGuy wrote:

SoundGuy wrote:
One always has the tow vehicle's 12 volt battery as temporary back up AND tow vehicle electrical system for temporary load support if necessary.

2oldman wrote:
Then that would suffice for a 6v failure also.

Not true, if one of two 6 volt trailer batteries fails one can't load support the remaining 6 volt with a truck's 12 volt electrical system.

Whoosh. No one said anything about supporting or supplementing a single 6 V. The need is for temporary/emergency power. Enough for the water pump so you can flush, or to pull the slide in so you can travel.

Disconnect the link between the 6 volts to get them out of the circuit, then jumper cable from vehicle to ground and +12. You now have the necessary 12 V power to handle the immediate need. Simple.

But, when's the last time you had a battery fail suddenly? I don't doubt that it has happened, but I can't recall hearing of any sudden failures of deep cycle batteries, and it's never happened to me - they die a slow death.

SoundGuy wrote:
One always has the tow vehicle's 12 volt battery as temporary back up AND tow vehicle electrical system for temporary load support if necessary.

2oldman wrote:
Then that would suffice for a 6v failure also.

Not true, if one of two 6 volt trailer batteries fails one can't load support the remaining 6 volt with a truck's 12 volt electrical system. If one of two 12 volt trailer batteries fails one can load support the remaining 12 volt with a truck's 12 volt electrical system.

Also, for those of us who have limited battery requirements we can choose to run just one 12 volt trailer battery, therefore only have to find a location to fit one battery, and on limited occasions when we might want to briefly power an inverter we can load support that one 12 volt trailer battery with the truck's electrical system, if necessary. Can't do that with a single 6 volt battery.

otrfun wrote:
Before this thread, I never gave alarm and shutdown voltage a lot of thought. Guess we lucked out with an inverter that supposedly shutsdown at 10.0 volts. Our previous inverter shutdown at 10.5 volts. Didn't realize some inverters shutdown at 11.0 volts or higher. Depending on system capability (batteries, cable length/size, etc.), a 1 volt difference like this could potentially be a huge deal in some dry camping situations. Going forward, we're definitely going to be looking much closer at alarm/shutdown voltage specs.

We don't dry camp often so I wasn't willing to invest a lot of $$$ in an inverter but decided to add one to our trailer a few years ago when found I could buy a "good enough" 1000 watt PSW for $200 Cdn at Canadian Tire. It's the only PSW inverter they sell and in reality is a Chinese manufactured NPower inverter, hardly high quality but does do what I want. It's low voltage alarm threshold is spec'd at 11.0 volts, +/- 0.3 volts, meaning it could alarm at even 11.3 volts - in reality I've found it starts to be unhappy around 11.5 volts. Both of the heavy loads I want it to run - toaster and coffee maker - are resistive loads, so excessive surge from an inductive load isn't an issue for me. If it were that would be a reason for a much better quality inverter capable of a much lower alarm threshold. Further to this though, if this inverter does shut down due to low incoming source voltage it's spec'd to not restart unless that incoming voltage rises to 11.6 volts, +/- 0.3 volts, meaning it might have to be as high as 11.9 volts before it would be willing to restart ... yet another reason a higher quality inverter that would restart at a lower voltage might for some be a better choice. No question about it, voltage drop and inverter low voltage threshold are just as important as which battery (or batteries) to use to power that inverter.

SoundGuy wrote:
One always has the tow vehicle's 12 volt battery as temporary back up AND tow vehicle electrical system for temporary load support if necessary.

Then that would suffice for a 6v failure also.

SoundGuy wrote:
One's preference for 6 volt or 12 volt jugs should be based on one's own situation and personal preference, not on biased views from either camp on the internet. ;)

Most every view on here is biased.

OP is gone. Hope he learned something.

I posted a vid of inverter use on microwave and my set up..

I guess we hijacked this guys thread long enough...

https://forums.goodsamclub.com/index.cfm/fuseaction/thread/tid/29556025/gotomsg/29556025/p/1.cfm#29556025

otrfun wrote:

ktmrfs wrote:

otrfun wrote:

ktmrfs wrote:
. . . if the pair of GC drops below about 75-80% SOC, you can hit the inverter shutoff limit pretty easy with loads of 800-1000 W. Some may depend on the specific inverter and what it's lower limit is.

Now if the batteriesa are above 80% or so, you in good shape. but that means keeping them near full charge when you want the inverter. So.... run the furnace at night then get up and turn on the toaster.... likely be a nope! low temps= higher internal resistance, lower capacity, coupled with partial discharge.

IMHO if your happy with your current 12V setup, don't mess with it. Or, get GC for most of the stuff and run the inverter off 1 or 2 12V AGM's or similar.

We had a situation where we had to run 35 ft. of 2/0 cable from a 1000 PSW watt inverter to two GC2 batteries. On a number of occasions we placed a 65 amp load on the batteries with the inverter (~700 watt a/c load) and regularly ran the two GC2 batteries down to 50% SOC with no inverter alarms or shutdowns. Output from the inverter was always stable at 117 vac. DC voltage drop (due to 35 ft. 2/0 cable) with the 65 amp load was approx. .35v (3%). This particular inverter was supposed to alarm at approx. 10.6v and shutdown at approx. 10.0v. It never alarmed or shutdown.

your inverter has a much lower threshold than mine does. mine alarms at 11.5V ad shuts down not much below that. From what BFL experienced I suspect his was similar to mine. You've got about another 1V margin, which would make a big difference. So, the GC work well with your combo. Another story with mine. So, yes sucess (or failure) is highly dependent on both the batteries and inverter.

Before this thread, I never gave alarm and shutdown voltage a lot of thought. Guess we lucked out with an inverter that supposedly shutsdown at 10.0 volts. Our previous inverter shutdown at 10.5 volts. Didn't realize some inverters shutdown at 11.0 volts or higher. Depending on system capability (batteries, cable length/size, etc.), a 1 volt difference like this could potentially be a huge deal in some dry camping situations. Going forward, we're definitely going to be looking much closer at alarm/shutdown voltage specs.

yes, shutdown voltage definitely can have a big effect, the difference between yours and mine highlights that.

at 10.6V open circuit (no draw) a flooded lead acid battery is at or near 0%SOC. Even with a C/10 discharge 10.6 is a very low state of charge.

I suspect different inverter designers have different philosophies on when to alarm and shut down and what to expect the typical user has for voltage drop on any line between the battery and inverter.

The best system would be to use a "4 wire" sense, hot and neutral carrying current and two wires back to the battery to measure the battery terminal voltage going to the shutdown circuit. that way you remove line drop from the equation. Don't know of any inverters that do that.

Now if it shuts down at 10.0 V under a heavy load, (C/3 or more) a GC the battery is likely above 10.6V, and has some margin. If it is this low with parallel 12V, IMHO not good, way to close to deep discharge. And if it doesn't shut down till 10V under a light load you risk running the battery way down near 0% SOC, not good for even good GC batteries.

But the 11.5ish shutdown on mine is going towards the other extreme of shutting down well before it needs to with GC, and somewhat above where it could discharge parallel 12V down to.

Would be nice if inverters had a selector, GC or 12V and then adjusted the shutdown voltage to account for battery internal resistance. It could even by a dynamic voltage, look at the current draw and determine internal drop, shut down lower at high draw, higher voltage at low draw.

ktmrfs wrote:

otrfun wrote:

ktmrfs wrote:
. . . if the pair of GC drops below about 75-80% SOC, you can hit the inverter shutoff limit pretty easy with loads of 800-1000 W. Some may depend on the specific inverter and what it's lower limit is.

Now if the batteriesa are above 80% or so, you in good shape. but that means keeping them near full charge when you want the inverter. So.... run the furnace at night then get up and turn on the toaster.... likely be a nope! low temps= higher internal resistance, lower capacity, coupled with partial discharge.

IMHO if your happy with your current 12V setup, don't mess with it. Or, get GC for most of the stuff and run the inverter off 1 or 2 12V AGM's or similar.

We had a situation where we had to run 35 ft. of 2/0 cable from a 1000 PSW watt inverter to two GC2 batteries. On a number of occasions we placed a 65 amp load on the batteries with the inverter (~700 watt a/c load) and regularly ran the two GC2 batteries down to 50% SOC with no inverter alarms or shutdowns. Output from the inverter was always stable at 117 vac. DC voltage drop (due to 35 ft. 2/0 cable) with the 65 amp load was approx. .35v (3%). This particular inverter was supposed to alarm at approx. 10.6v and shutdown at approx. 10.0v. It never alarmed or shutdown.

your inverter has a much lower threshold than mine does. mine alarms at 11.5V ad shuts down not much below that. From what BFL experienced I suspect his was similar to mine. You've got about another 1V margin, which would make a big difference. So, the GC work well with your combo. Another story with mine. So, yes sucess (or failure) is highly dependent on both the batteries and inverter.

Before this thread, I never gave alarm and shutdown voltage a lot of thought. Guess we lucked out with an inverter that supposedly shutsdown at 10.0 volts. Our previous inverter shutdown at 10.5 volts. Didn't realize some inverters shutdown at 11.0 volts or higher. Depending on system capability (batteries, cable length/size, etc.), a 1 volt difference like this could potentially be a huge deal in some dry camping situations. Going forward, we're definitely going to be looking much closer at alarm/shutdown voltage specs.

Atlee wrote:
At the same time, the idea of an unexpected GC2 battery failure is also blown out proportion.

2oldman wrote:
By that logic, a single 12v battery camper should always carry a spare battery.

One always has the tow vehicle's 12 volt battery as temporary back up AND tow vehicle electrical system for temporary load support if necessary. I carry just one 12 volt and have no concerns at all I'll ever be stranded as I also have a lithium ion jump starter to cover the truck so I know I can always get it started, regardless. And yes, I've been doing both for several years now and for my purposes both methods work just fine. One's preference for 6 volt or 12 volt jugs should be based on one's own situation and personal preference, not on biased views from either camp on the internet. ;)