diy solar

diy solar

High frequency verses low frequency inverters

k490

Solar Enthusiast
Joined
Nov 26, 2022
Messages
332
Location
Phoenix, Arizona
What is the difference between high, or low frequency inverters the pros and cons? I have seen a few posts someone said low was better for high surge load like AC units, pool pumps. Another thing I read low frequency can handle more power. Is a low frequency same as a modified sinewave?
 
Is a low frequency same as a modified sinewave?

I don't know much about low vs high frequency, but what you've said so far (except the quote above) more or less concurs with what I know.

No - low frequency isn't the same as modified sinewave. There are high and low frequency modified sinewave inverters as well as low/high pure sine wave ones.

I just got my first low-frequency inverter. It's only 1000W, but it has powered up to an 1850W (2500W surge) Dyson vacuum with no problem. Now it can't run it for very long, I think it started beeping around 30 seconds and I let it run another 15-30 seconds before turning it off, but at that point the inverter had yet to shut down due to overload. This is a Victron inverter.

My previous inverter was not low-frequency and was 2000W. While it could run everything higher powered (like the vacuum), it just seemed to struggle more to do so. This was an Renogy. It had a huge idle draw (compared to the eco mode idle draw of the Victron) and so it was draining our battery bank just to be powered on, which we needed 24/7 to keep the fridge cool.
 
Low frequency = larger transformer.

The fet switching rate is lower because the winding of the larger transformer takes longer to charge up to the given voltage it wants to see at that time point in 60 HZ ac sine wave.
 
Low frequency inverters are heavier and more expensive to build. They are better at starting large inductive loads or dealing with multiple sure loads.

High frequency is lighter and cheaper to build. This is the primary reason why they are made. For me, I have way too many inductive loads and may be welding when one of them kicks in. So low frequency inverters for me.
 
I had a 1500 watt Cotek HF inverter that was very good with inductive loads. It would grunt and complain for a second when the fridge kicked on, you could hear the FETs buzz...sort of like a hissing sound. But it always recovered and kept on going. Now I'm using a Growatt LF AIO. That big heavy transformer makes it a real pain to mount on the all but it runs the whole house. Even the 1hp well pump is no problem. I understand the Growatt HF inverters in parallel for 120/240 split phase also handle the inductive surge loads very well.

Modified sinewave is old technology and you don't want to consider it.
 
I have a Xijia Cnswipower 6000w HF.

I can weld with it and use a 2.5hp belt driven air compressor. Not that i do everyday but it's good to know it can do it :)
 
I had a 1500 watt Cotek HF inverter that was very good with inductive loads. It would grunt and complain for a second when the fridge kicked on, you could hear the FETs buzz...sort of like a hissing sound. But it always recovered and kept on going. Now I'm using a Growatt LF AIO. That big heavy transformer makes it a real pain to mount on the all but it runs the whole house. Even the 1hp well pump is no problem. I understand the Growatt HF inverters in parallel for 120/240 split phase also handle the inductive surge loads very well.

Modified sinewave is old technology and you don't want to consider it.
Absolutely concur with this.

My take is that if you are going to be pushing your inverter near it’s rated limits and you have inductive loads, LF is probably the better option.

But if you greatly overdubbing the inverter capacity for actual demand and have a per-leg rating that easily exceeds the surge of any inductive load, there is little/no difference (other than the lower cost of HF inverters).

The Schneider Conext SW 4048 can deliver 3800W continuous and up to 7000W for 5 seconds. Maximum imbalance is not clearly spelled out but is almost certainly under 100% (cannot deliver only 7000W of peak power to a single leg). The 41A peak current would translate to no more than 4920W to a single leg regardless of whether 100% imbalance is supported or not.

The Conext SW 4048 costs over $1700.

Contrast that with this dual-HF alternative SRNE inverter rebadged by Y&H costing the same or less: https://www.amazon.com/Inverter-Spl...9Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU=

5kW per leg sustained and 10kW per leg surge capability (with no issue supporting 100% imbalance).

The Conext SW4048 weighs 62 lbs while the Y&H 10K weighs 46lbs.

Don’t get me wrong - I realize a Schneider inverter is an entirely different class of quality and reliability than an SRNE inverter rebadged by Y&H so a large portion of this ‘equal’ pricing needs to be allocated to that and for the same price, the Conext SW4048 is probably the better buy.

But this illustrates my point: the dual-HF option can surge to more than twice the power of the Schneider LF alternative and can also sustain 232% as much power.

If you need more than what the Conext SW 4048 can deliver, you will need to pay more for it.

The Conext XW 6048 costs about double the price of the Conext SW 4048 and weighs 126lbs.

The XW 6048 can deliver 6000W continuous (still less than the Y&H) and can surge to 12,000W for 15 seconds (still less than the Y&H) but supports a L-N surge current of up to 105A = 12,600W which is 126% of the SRNE dual-HF peak current capability.

But for that you will pay about twice as much and have a LF inverter weighing almost 3 times as much.
 
The thread below covers the pros & cons of each design. Really comes down to your specific situation. I have used both but now only use the LF type. Cheap out of Alibaba and they don't go bang when abused.

 
The thread below covers the pros & cons of each design. Really comes down to your specific situation. I have used both but now only use the LF type. Cheap out of Alibaba and they don't go bang when abused.

Appreciate your perspective (especially since you’ve used both).

Other than pushing power output close to rated limits, can you comment on what other types of ‘abuse’ your LF inverters handled better than your HF inverters?
 
The thread below covers the pros & cons of each design. Really comes down to your specific situation. I have used both but now only use the LF type. Cheap out of Alibaba and they don't go bang when abused.

Care to share any of the LF and or storefronts you trust / would recommend?
 
Does the low frequency tend to be rated to higher power levels?
Not exactly. But it does have an easier time starting inductive loads, like motors. The 0.2 to 3 seconds of surge power can be much greater in an inductive load like a refrigerator compressor motor. Ours is smallish, 7.4cf and requires up to 850W to start up, but once out of surge mode, it purrs along at 70W. No problem you say, my 2000W high frequency inverter has a surge of 4000W. Yes but. The catch is it most likely can only surge to 4000W for a split second and then it crashes. So if you have a well pump that needs 3200W surge for 1 second to start, then a 4000W surge ability is pointless if it can’t sustain for longer than 0.05 of a second. Maybe it can sustain a 3200W surge for 0.5 of a second, but remember, your pump needs a solid whole 1.0 second to start up. Without it, the pump will not start. It’s like moving a light switch 0.1 of an inch and expecting the switch to turn on the light.
 
Does the low frequency tend to be rated to higher power levels?
LF inverters have an integrated Autotransformer which allows unused power on one leg to be redirected to the other leg so that max power per leg can exceed 50% of overall power rating.

Dual-HFs can only deliver 50% of maximum rated power to each leg.

Historically, the Autotransformer adds enough cost that lower-powered LF inverters were rare and most HF inverters tended to be single-phase.

MPP Solar and others pioneered the architecture of syncing two low-powered single-phase HF inverters to deliver split-phase power.

The first model I’m aware of was the LV2424 which could deliver 2.4+2.4 = 4.8kW in a dual-inverter split-phase configuration.

Then MPP Solar introduced their 6kW split-phase midel which is essentially 2 3kW HF inverters in a single box.

The trend towards higher-powered dual-HF inverters has continued with Signature Solar introducing their own 6kW model and now this 5+5 = 10kW model introduced by SRNE.
 
Not exactly. But it does have an easier time starting inductive loads, like motors. The 0.2 to 3 seconds of surge power can be much greater in an inductive load like a refrigerator compressor motor. Ours is smallish, 7.4cf and requires up to 850W to start up, but once out of surge mode, it purrs along at 70W. No problem you say, my 2000W high frequency inverter has a surge of 4000W. Yes but. The catch is it most likely can only surge to 4000W for a split second and then it crashes. So if you have a well pump that needs 3200W surge for 1 second to start, then a 4000W surge ability is pointless if it can’t sustain for longer than 0.05 of a second. Maybe it can sustain a 3200W surge for 0.5 of a second, but remember, your pump needs a solid whole 1.0 second to start up. Without it, the pump will not start. It’s like moving a light switch 0.1 of an inch and expecting the switch to turn on the light.
You raise a good point.

This is the manual for the 5+5=10kW SRNE HF Split-phase model: https://www.srnesolar.com/wp-conten...ase_solar-charger-inverter_usermanual_1.4.pdf

It can deliver 5kW sustained per leg and 10kW peak per leg but with no surge time specified.

On the other hand, it is specified to have a ‘Load Capacity of Motors’ of 6HP, which requires 4474W sustained and a minimum (Class A) locked-rotor amps @ 30% sag of 109A meaning 9.2kVA.

Would you have any concerns about this 5+5=10kW dual-HF inverter having difficulty with any inductive motor load that a 5kW LF inverter could handle (assuming less than +100% surge rating)?
 
You raise a good point.

This is the manual for the 5+5=10kW SRNE HF Split-phase model: https://www.srnesolar.com/wp-conten...ase_solar-charger-inverter_usermanual_1.4.pdf

It can deliver 5kW sustained per leg and 10kW peak per leg but with no surge time specified.

On the other hand, it is specified to have a ‘Load Capacity of Motors’ of 6HP, which requires 4474W sustained and a minimum (Class A) locked-rotor amps @ 30% sag of 109A meaning 9.2kVA.

Would you have any concerns about this 5+5=10kW dual-HF inverter having difficulty with any inductive motor load that a 5kW LF inverter could handle (assuming less than +100% surge rating)?
I’m assuming that OP is referring to cheap single phase high frequency 500-2000W inverters. Like the 2000W 12v Renogy we paid about $250 for.

You speak of higher quality and higher functional high frequency inverters which can make for a good value.
 
I’m assuming that OP is referring to cheap single phase high frequency 500-2000W inverters. Like the 2000W 12v Renogy we paid about $250 for.
I was responding to this statement from his original post:

‘I have seen a few posts someone said low was better for high surge load like AC units, pool pumps.’
You speak of higher quality and higher functional high frequency inverters which can make for a good value.
Yes, I have a hard time seeing anyone develop a split-phase solution under 2000+2000W…

And I believe Solark is HF (though priced like LF :)).
 
Does anyone make a LF high capacity AIO? Suspect not, as that expense segment tends to be willing to assemble individual components.
 
But no built in solar. As far as I could tell. I mean, the beauty and the curse of the AIO/Hybrid units is that its all under one roof. So to speak. The curse of course is getting it right, especially software wise. The link has MPPT controller in it, but I cannot find a product in their lineup that does all three. Yes, LF. But clearly English language challenged.....
 
But no built in solar. As far as I could tell. I mean, the beauty and the curse of the AIO/Hybrid units is that its all under one roof. So to speak. The curse of course is getting it right, especially software wise. The link has MPPT controller in it, but I cannot find a product in their lineup that does all three. Yes, LF. But clearly English language challenged.....
240A MPPT = built-in solar charge controller…
 
Back
Top