Pure sine wave inverter power question

[John Wolf]

I have a 12v200ah lifepo4 with 200a bms/400a max...is there a downside or danger with using a 3000w/6000wp pure sine wave inverter? Also, charging with Victron Smartsolar 100v/50a controller.

 

[John Frum]

I have a 12v200ah lifepo4 with 200a bms/400a max...is there a downside or danger with using a 3000w/6000wp pure sine wave inverter?

Which BMS do you have?
Its unusual for a BMS rated for 200 amps continuous to have any significant surge duration at 400 amps.

3000 ac watts / .85 conversion factor / 10 volts low cutoff = 352.941176471 service amps.
I expect most 200 amp BMSs would die in minutes if exposed to 350ish amps of current.

 

[time2roll]

You have the potential to exceed the discharge rating of the battery and reducing the battery life. I recommend 400 ah for 2000 watts and 600 ah for 3000 watts as a minimum. I also recommend 24 volts or higher to drive a 3000 watt inverter.

 

[sunshine]

I have a 12v200ah lifepo4 with 200a bms/400a max...is there a downside or danger with using a 3000w/6000wp pure sine wave inverter?

No problems. It would would eliminate one weak link during momentary power surges and allow for future upgrades.

What if you use one battery/ inverter lead as recommended from a smaller inverter (say the 2000w model or calibrate your own to match) that will activate the low voltage inverter disconnect at loads below that of the BMS?
I would just limit the loads rather than do this but it is a possible solution to those concerned about the BMS being called upon as a circuit breaker.

 

[chrisski]

Your BMS likely limits you to 100 amps or 1200 watts or 200 amps and 2400 watts, so not enough power for a 3000 watt inverter, especially if you will use it for any length of time.

Idle draw is also a problem. I have a 24 volt 300 watt inverter that has a normal idle draw of .3 amps, or 7.2 watts. In eco mode, that inverter will automatically uses next to nothing. I also have a 12 volt 2000 watt inverter that has an idle draw of 1 amp or 12 watts. No ecomode for that. So a larger than needed inverter will lead to more than needed draw. Just to power that 2000 watt invert I mentioned with your 200 ah of batteries, depletes your batteries by 12%. This and other idle draws adds up quickly.

 

[Tecnodave]

Old school thinking....

12 volts......starting/pretend deep cycle.....1000 watts
12 volts ......real deep cycle (no CCA rating....cold cranking amps) 1500-2000 watts
24 volts......real deep cycle...CG-2 or L-16 batteries 3000-4000 watts
48 volts.........” “ “ “ “ 4000-6800 watts

My system is 24 volts with two banks L-16 552 amp hour (real solar batteries) 4000 watts


the higher the battery voltage the less the current , less inverter loss

12 volt inverter 85% efficiency
24 volt inverter 93% efficiency
48 volt inverter 95% efficiency

there is a voltage drop across the switching devices in the inverter, the drop stays the same no matter the battery voltage so it is a lesser percentage the higher the battery voltage

 

[chrisski]

My system is 24 volts with two banks L-16 552 amp hour (real solar batteries) 4000 watts

I think 4000 watts is a bit much. More of a wire size thing than the batteries.

When you say 4000 watts, how exactly do you define that?

For me, I say 12 volts is good for 1000 watts, but you can have a 2000 watt inverter to make brief excursions above 1000 watts, like to warm, not cook food for a couple minutes at a time, four to six times a day. Wiring would be 2/0 or 4.0. Not to run 2000 watt appliances like an air conditioner.

I say 24 volts is good for 2000 watts. With that I will run my microwave as much as I want to cook food. Even the frozen chicken pot pie that takes 20 minutes. I may run an air conditioner with a 24 volt system if it a 3000 watt inverter will start it, but constant draw will be about 1000 watts (80 amps).

I like the idea of sticking to a 100 amp limit to avoid wire from getting too thick.

These are some of the links from my signature block that have me stick to some rather low limits: 12 Volt Safety Design [] Basics of OffGrid Design [] Batteries and Inverters

 

[sunshine]

Just to power that 2000 watt invert I mentioned with your 200 ah of batteries, depletes your batteries by 12%. This and other idle draws adds up quickly.

A lot of the generic brands specs do not differentiate idle consumption between sizes and may not be a problem with the newer high freq types.

so not enough power for a 3000 watt inverter

3000w is just the label on the side. You determine the power through a inverter up to its rating and for many brands buying 3000w when you worked out you need only 2000w means you understand the actual quality.

 

[Tecnodave]

With my system a very small inverter will fill my needs for daily use, i do not cook electrically , so referigeration....danfoss compressor at 24 volts 42 watts start and run, led lights , I use an Exeltech which is the quietest inverter made (EMI/RFI) , no noise in the stereo, etc, but i do run a 240 volt deep well pump that will tax my MagnaSine 4000 watt inverter, only when I run the deep pump do i parallel the battery sets, when on low power mode i run only one bank. My Rolls-Surette S-530 true solar deep cycle batteries are now nearing 26 years old.......still at 1.265 s.g. My Exeltech inverter is 22 years old and the MagnaSine is nearly that.......that is a direct result of very conservative design. My MPPT controllers are capable of 150 volts, 86 amps....i run them at 72 volts and 45 amps DC out, very conservative ........never had a total system failure, one Cotek 1500 watt inverter died but throwing a few breakers, power up in less than 5 minutes......again very conservative design

 

[wholybee]

Sure you can use a 3000W inverter. Just use a smaller fuse. I have a 150A fuse on my 3000W inverter. I only need 1200W, but was gifted a 3000W.

 

[John Wolf]

Which BMS do you have?
Its unusual for a BMS rated for 200 amps continuous to have any significant surge duration at 400 amps.

3000 ac watts / .85 conversion factor / 10 volts low cutoff = 352.941176471 service amps.
I expect most 200 amp BMSs would die in minutes if exposed to 350ish amps of current.

The ampere time plus has a 200a bms with 400 max.

 

[John Wolf]

No problems. It would would eliminate one weak link during momentary power surges and allow for future upgrades.

What if you use one battery/ inverter lead as recommended from a smaller inverter (say the 2000w model or calibrate your own to match) that will activate the low voltage inverter disconnect at loads below that of the BMS?
I would just limit the loads rather than do this but it is a possible solution to those concerned about the BMS being called upon as a circuit breaker

Yes, I was looking for future upgrades, as well as higher spike protection. I was going to limit the loads too as protection.

 

[John Wolf]

You have the potential to exceed the discharge rating of the battery and reducing the battery life. I recommend 400 ah for 2000 watts and 600 ah for 3000 watts as a minimum. I also recommend 24 volts or higher to drive a 3000 watt inverter.

If I limit discharge manually, would there be any potential for reducing battery life? I was going to use under the battery rating anyway, the 3k/6k inverter was more of a future upgrade and spike protection idea.

 

[John Wolf]

Your BMS likely limits you to 100 amps or 1200 watts or 200 amps and 2400 watts, so not enough power for a 3000 watt inverter, especially if you will use it for any length of time.

Idle draw is also a problem. I have a 24 volt 300 watt inverter that has a normal idle draw of .3 amps, or 7.2 watts. In eco mode, that inverter will automatically uses next to nothing. I also have a 12 volt 2000 watt inverter that has an idle draw of 1 amp or 12 watts. No ecomode for that. So a larger than needed inverter will lead to more than needed draw. Just to power that 2000 watt invert I mentioned with your 200 ah of batteries, depletes your batteries by 12%. This and other idle draws adds up quickly.

excellent points you make, didn't thing of idle draw problems associated with excess inverter power.

 

[John Wolf]

I think 4000 watts is a bit much. More of a wire size thing than the batteries.

When you say 4000 watts, how exactly do you define that?

For me, I say 12 volts is good for 1000 watts, but you can have a 2000 watt inverter to make brief excursions above 1000 watts, like to warm, not cook food for a couple minutes at a time, four to six times a day. Wiring would be 2/0 or 4.0. Not to run 2000 watt appliances like an air conditioner.

I say 24 volts is good for 2000 watts. With that I will run my microwave as much as I want to cook food. Even the frozen chicken pot pie that takes 20 minutes. I may run an air conditioner with a 24 volt system if it a 3000 watt inverter will start it, but constant draw will be about 1000 watts (80 amps).

I like the idea of sticking to a 100 amp limit to avoid wire from getting too thick.

These are some of the links from my signature block that have me stick to some rather low limits: 12 Volt Safety Design [] Basics of OffGrid Design [] Batteries and Inverters

I need a system that will run a couple of fridges and a freezer, modem/router, device battery chargers, couple led lamps, maybe a small floor fan.

 

[sunshine]

If I limit discharge manually, would there be any potential for reducing battery life?

Battery life is the same whatever inverter size you use if you have the same load on each one.
You need to check the idle requirement for that particular model and size before drawing any further conclusions as they vary across brands and sizes. However, as stated previously there isn't usually a big difference, if any, with the newer types.

 

[John Wolf]

A lot of the generic brands specs do not differentiate idle consumption between sizes and may not be a problem with the newer high freq types.

3000w is just the label on the side. You determine the power through a inverter up to its rating and for many brands buying 3000w when you worked out you need only 2000w means you understand the actual quality.

My thoughts too, and also having more power to expand rather than limit power, is there a downside to this thinking? I can't think of one.

 

[sunshine]

My thoughts too, and also having more power to expand rather than limit power, is there a downside to this thinking? I can't think of one.

The only downside is that in buying an oversized inverter to compensate for any label disinformation, to run much smaller loads is the realisation that those smaller loads are actually the optimum for that inverter. There isn't much extra capacity in modern high frequency generic inverters specially when it comes to start up loads. Thus the reason why it is best to go big at first.

 

[time2roll]

If I limit discharge manually, would there be any potential for reducing battery life? I was going to use under the battery rating anyway, the 3k/6k inverter was more of a future upgrade and spike protection idea.

Yes if you only load up the inverter to 1000 watts max you will have no issues.

 

[chrisski]

The only downside is that in buying an oversized inverter to compensate for any label disinformation, to run much smaller loads is the realisation that those smaller loads are actually the optimum for that inverter. There isn't much extra capacity in modern high frequency generic inverters specially when it comes to start up loads. Thus the reason why it is best to go big at first.

One thing to add on to this on output going down as heat goes up, and maybe needing to get a bigger than expected inverter.

Being in Phoenix, summers are hot, and if I am using an inverter which is outside, I need to watch heat.

I bought a 300 watt continuous inverter, which once internal temps get to 105 F, the output is reduced to 240 watts. 105 F is a cold day in some of our summers, so as the temps go up, at 165, the output is further reduced to about 165 watts.

So, when putting this outdoor solar “generator” together, I had to watch this reduced output as heat goes up. The fan won’t cool down the inverter more than the outside temp. I’ve measured outside temps on my RV when its been shut off for days with nothing running from 170 F for a black panel on the side, to 154 F for flexible solar panels on top, 134 for a different set of glass solar panels, and inside temps were 105.

For my next project, the inverter can’t be housed in the air conditioned portion of the RV, but will be in pass through storage. If I do use solar AC, if this inverter’s output is reduced by 50% because of heat, then I may need to go larger than what I had thought at first.