Inverter too small?

[patchedup]

I have a 1000w cobra inverter i bought to power a small 5 cubic foot freezer that pulls 4 amps when running. The battery i use for the inverter is 105 amp marine deep cycle group 29.The inverter is connected to the battery with shortened battery jumper cables, at about 3 feet long, from the battery to the inverter. After about 5 hours the alarm on the inverter sounds and indicates low input voltage of less than 11 volts. The battery at startup was charged up showing 13 volts on my meter. Is the inverter too small or is the battery to small? I thought i could run the freezer with this setup for at least 18 hours. With this info i can forget running my cpap off this setup for overnight. Thanks!!!!

[time2roll]

If the inverter was too small the freezer would not start.
You need two or three more batteries and a good method to charge.

[MrWizard]

not enouugh battery
also the smaller the fridge the more it cycles (more run time per hr)
larger fridge more insulation and moe efficent operation

my fridge draws approximately 100w, 1 amp 120vac aka 10amps 12vdc , but start up surge is around 900w

your 4 amps is likely Max rating, no way did you draw 44amps dc continuous for 5 hours, frrom that singlee battery

btw...many members run a cpap from a single batteryat night
but Not a cpap and fridge , for that you need more batteries

[2oldman]

These answers are getting more obscure and off point.

[MNtundraRet]

Your batteries no longer charge to full charge. What do your batteries read 12 hours after charging and removing shore-power?

Reading the meter with RV plugged in just tells you charging is taking place. The battery could be no where near full charge. A 1000 watt inverter most likely uses 0.6 amps each hour for over-head. Did you use a clamp-on meter to check the amps off the cable between inverter and the battery? That would have given you the amps expected to be used each hour.

My 1000 watt inverter requires 6 gauge cable (about 2 to 3 feet). Anything smaller will cause a larger "load drop" on voltage and premature "low battery" shut-down.

I suspect your battery may be sulfated and recharging to only 50 to 60% new capacity.

[enblethen]

I would check your "shortened battery jumper cables" wire size and type of wire. They could be #6 aluminum. Could be poor connections. Both of which will increase volatage drop.
1000 watts could draw around 80 amps.
Refer should draw about 40 amps at 12 volts while running.

[2edgesword]

Do battery manufacturers use the same standards (allowable voltage drop and same load) to test batteries in order to establish amp-hour ratings.

My understanding is that amp-hour ratings can be manipulated to achieve higher ratings by allowing for a greater drop in voltage during the test to establish the rating. If one manufacturer uses a 12.3V limit while another uses an 11.8V limit they may call them both 105 amp-hour batteries but you're not going to get the same performance. I would think there is an industry standard for setting amp-hour ratings but I'm not aware of it.

The amperage used by the manufacturer to establish the amp-hour rating can also have an affect. You can establish a longer amp-hour rating by drawing a lower current over a longer time.

[jpfx]

x3 also don't (ever) use over 50% of capacity before recharging if you want the battery to last.

[Chris_Bryant]

2oldman wrote:
Inverter is fine, you have inadequate battery.

x2- remember, 4 amps @ 120 vac is ~44 amps @ 12 vdc. I am amazed you could run it that long.

[2oldman]

Inverter is fine, you have inadequate battery.