Inverter question

[NeonNinja]

An aunt of mine bought the RCT Megapower RCT MP-T1000S Pure Sine Wave. She says it lasts only a short while especially with the fridge plugged in. Needs 6-8 hours of backup.

Any advice?

 

[Lupus]

Tell her to return it, unless she bought it second hand and someone abused it, the battery will only last as long as whatever is plugged into it, is it only a fridge? How old is the fridge?

 

[biena]

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www.makro.co.za

Read the reviews and don't buy it. Sounds like it has a lead acid battery 1 X 100AH GEL BATTERY
It won't last.

Advice return it, get something better. Do a bit of research first.

Some math with my fridge freezer (you will need to see what your aunts fridge uses)
seems to cycle every 30 minutes using
130W (max power usage) * 8 (hours of backup needed) / (2 to get a cycle of 30mins) + 4W (minpower usage) * 8 (hours of backup needed)= 536 W

That is just for the fridge/freezer, The inverter itself requires some power to run, cannot find info on what that unit draws.
Lets be generous and say 50W

50W * 8 = 400W

So that gives 536W + 400W = 936W, the 100AH gel battery 12V= 1200W (theoretically max)
If you deep discharge gel batteries you will kill it.

80% DOD is the maximum safe discharge for industrial semi-traction type deep-cycle flooded, AGM and GEL batteries. Do not continually discharge any lead-acid battery >80%. This will damage (or kill) the battery. Recommended maximum DOD for flooded batteries is 50% of capacity.

So what does that mean
1200W * 80% = 960W usable power

Factor in temperature and it can be even less.

lasts only a short while especially with the fridge plugged in

So what else is plugged in ? I'm afraid that battery is probably dead.

 

[NeonNinja]

Thanks guys. I’ve advised her to return it. Will be looking at something more expensive

 

[wingnut771]

Need a lithium battery, lead acid is dead but why need fridge backup for 8 hours? Surely it stays cold anyway in that time if you don’t open the door and put ice packs inside?

 

[denmendez65]

Need a lithium battery, lead acid is dead but why need fridge backup for 8 hours? Surely it stays cold anyway in that time if you don’t open the door and put ice packs inside?
View attachment 1897458

Plenty cold. I think she is connecting more stuff to it. A single LIPO battery might not be enough. As Lupus suggested, they need to check what loads they are putting on the inverter. I am skeptical the battery just died after a short while. LA is bad but not that bad.

 

[wingnut771]

Plenty cold. I think she is connecting more stuff to it. A single LIPO battery might not be enough. As Lupus suggested, they need to check what loads they are putting on the inverter. I am skeptical the battery just died after a short while. LA is bad but not that bad.

Lead acid is bad if you putting 1kW on a 100Ah. That will die a quick death even if you follow the 50% DoD rule. Also the peukert effect, will probably only get 20Ah out of it.

 

[denmendez65]

Lead acid is bad if you putting 1kW on a 100Ah. That will die a quick death even if you follow the 50% DoD rule. Also the peukert effect, will probably only get 20Ah out of it.

Again, loads. A fridge is not 1kW. So shes connecting more stuff than mentioned, not just a fridge.

 

[wingnut771]

Again, loads. A fridge is not 1kW. So shes connecting more stuff than mentioned, not just a fridge.

I was just illustrating a point:


LFP battery will still give full capacity:

 

[denmendez65]

Again, loads. A fridge is not 1kW. So shes connecting more stuff than mentioned, not just a fridge.

And running 1kW is not what those trolleys are for. You will drain the Lipo in 40 minutes. Those things are for a small TV, laptop and 1 light. They are not getting 8 hours, nowhere close to that. Even 2 lipo batteries running at 500W will be dead in 3.5 hours.

They need to adjust their expectations and either spend for a 5kWh battery system or just use the cheapie for what it is intended for, a laptop and a light or 2. A TV wont run long on the one you sent also.

 

[denmendez65]

I was just illustrating a point:
View attachment 1897475
View attachment 1897476
LFP battery will still give full capacity:
View attachment 1897477

Yeah I know that. For them to get the 80ah out of a GEL they need to run a max load of 60W.

I had those Lalela trollies with a single GEL battery. It lasted me 3 years as all it powered was my laptop and 2 USB lights with the monitor. It pushed me right through the load shedding period and woul get around 12 o 18 hours out of it before the alarm kicked in and the inverter cut off.

 

[wingnut771]

And running 1kW is not what those trolleys are for. You will drain the Lipo in 40 minutes. Those things are for a small TV, laptop and 1 light. They are not getting 8 hours, nowhere close to that. Even 2 lipo batteries running at 500W will be dead in 3.5 hours.

They need to adjust their expectations and either spend for a 5kWh battery system or just use the cheapie for what it is intended for, a laptop and a light or 2. A TV wont run long on the one you sent also.

I was just illustrating capacity difference between gel and LFP.

Lets do 200W load:

LFP:

 

[denmendez65]

They need this. And the inverter can be used with panels at a later stage if they want. No point getting a smaller inverter as a 1kW is some 2.5k, the 6,2kW is about 5.4k with 12kW overload, 6000W MPPT etc.

Either she adjusts or ups the budget considerably.

 

[wingnut771]

They need this. And the inverter can be used with panels at a later stage if they want. No point getting a smaller inverter as a 1kW is some 2.5k, the 6,2kW is about 5.4k with 12kW overload, 6000W MPPT etc.

Either she adjusts or ups the budget considerably.
View attachment 1897483

The rabbit hole is very deep.

 

[denmendez65]

The rabbit hole is very deep.

Very true. But the options out there have poor ROI. Check this. The first one is crap compared to the 6.2kW. Second one is LA batteries, 3rdone not sure. 4th is just 1kW. At least the 6kW can be hooked up to some 12 panels without issues and run the whole house at a later stage. The options below are just crap from a ROI POV.

What is that saying again? The cheapest upgrade is the load you dont run or something like that.

 

[wingnut771]

Very true. But the options out there have poor ROI. Check this. The first one is crap compared to the 6.2kW. Second one is LA batteries, 3rdone not sure. 4th is just 1kW. At least the 6kW can be hooked up to some 12 panels without issues and run the whole house at a later stage. The options below are just crap from a ROI POV.

What is that saying again? The cheapest upgrade is the load you dont run or something like that.
View attachment 1897491

Spit. Modified sine wave inverters should not even be a consideration so please chuck out those first 2.

 

[denmendez65]

Spit. Modified sine wave inverters should not even be a consideration so please chuck out those first 2.

How did you tell they are Mod sine?

 

[wingnut771]

How did you tell they are Mod sine?

I know what the OG mecer trolley inverter looks like. Im sure if you click on it it will confirm my suspicions.

 

[denmendez65]

I know what the OG mecer trolley inverter looks like. Im sure if you click on it it will confirm my suspicions.

Yep, says simulated sine wave but you have to go into the manual to see that.

 

[wingnut771]

Yep, says simulated sine wave but you have to go into the manual to see that.

Or just look at the pic or scold geewiz for not putting it in the heading.