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Old 07-02-2021, 11:16 PM   #1
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Inverter surg time

I'm looking at Xantrex Freedom X 3000w and a Samlex PST-3000, both 12v.

The Xantrex specs state surge is 6000w >2seconds.
https://www.xantrex.com/documents/Po..._Datasheet.pdf

The Samlex specs state surge is 6000w <8ms
https://samlexamerica.com/wp-content...-1119_Hrez.pdf

This SMA is 100ms.
https://files.sma.de/downloads/SBSXX...716.1625282587

Seems to be a HUGE difference in times.

I get it depends on what type of load is causing the surge. A larger motor vs a smaller refrigerator would have a longer surge.

I'm running a 450ah AMG bank. My biggest AC draws are a 1000w microwave, a 750w mini-split or a 700w Instant pot, so I'm not really worried about surges...but I'm really confused how the surge times are so different.

If anyone can help explain these differences, it would be appreciated.

Thanks.

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Old 07-03-2021, 03:31 AM   #2
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These specs are not comparable from one company to another, only within a given line.

And they are meant to show how long the unit can withstand such a surge

it is not the inverter that produces a surge, but the load

up to the owner to ensure buying a robust enough unit and/or reducing surges to a level that doesn't result in early death.

I would go with Samlex over Xantrex, even if the latter were superior, their attitude toward customers and after sales support are truly horrific, once the warranty is over even their certified service centers have a very hard time being able to repair anything.

But IMO Magnum is top dog for high end inverter / chargers, followed closely by Victron.
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Old 07-03-2021, 10:26 AM   #3
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Originally Posted by john61ct View Post
These specs are not comparable from one company to another, only within a given line.

And they are meant to show how long the unit can withstand such a surge

it is not the inverter that produces a surge, but the load

up to the owner to ensure buying a robust enough unit and/or reducing surges to a level that doesn't result in early death.

I would go with Samlex over Xantrex, even if the latter were superior, their attitude toward customers and after sales support are truly horrific, once the warranty is over even their certified service centers have a very hard time being able to repair anything.

But IMO Magnum is top dog for high end inverter / chargers, followed closely by Victron.
I agree with the owner being responsible overall. I'm fortunate to have a friend who is a solar expert (set up huge systems internationally) and have researched the topic pretty extensively (still don't know s..t).

Part of my responsibility is understanding the true capability of system components so I can stay within them.

I agree with Magnum and Victron (which doesn't provide a surge rating or time in their spec sheet), yet I have a budget to work with.

All that said, my question was "why" are the surge times different and how does that make a difference overall.

If Xantrex has a "true" 2 second surge at 6000w, what is Samlex's "true" comparative 2 second surge rating....4000w? 4500w?
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Old 07-03-2021, 10:27 PM   #4
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Thereís a bit of difference in surge capacity difference built into low frequency vs high frequency inverters, with high frequency units having surge times in the milliseconds vs full seconds for low frequency designs.

One is based on bigger, heavier components and the other is more like a switching power supply in a computer with smaller fets. Itís a cheaper design, but lighter and maybe more efficient, so itís kind of a trade off, but I prefer the low frequency units personally. They may be less well suited to a driving bus, however, cause those heavy parts probably donít like bumps nearly as much over time.
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Old 07-04-2021, 08:15 AM   #5
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Thereís a bit of difference in surge capacity difference built into low frequency vs high frequency inverters, with high frequency units having surge times in the milliseconds vs full seconds for low frequency designs.
Thank you for a clear response and the education.

I do not think the Xantrex is a low frequency inverter for a few reasons. It doesn't say so, and the price point, especially for its wattage rating.

Can you see in the link spec sheet where this identifies it as a low frequency?
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Old 07-04-2021, 08:58 AM   #6
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Can you see in the link spec sheet where this identifies it as a low frequency?
Neither seem to specify either way. I would also lean towards this being the case (one being HF and the other LF) but both seem substantially large enough it could go either way. Maybe the specified weight would give it away, idk.



Outside of that, I wonder if internal capacitance can possibly create that kind of gap.
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Old 07-04-2021, 09:04 AM   #7
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I donít know how to tell via the spec sheet but from what I understand if you have a surge time like that itís very, very likely low frequency.

You probably can get an idea by comparative weights too if I had to guess.
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Old 07-04-2021, 09:17 AM   #8
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Little googling: https://www.ntea.com/NTEA/Member_ben...erterline.aspx

Turns out itís a high frequency unit but they designed it with that surge time specifically as a feature that seems pretty novel in the industry.
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Old 07-04-2021, 01:15 PM   #9
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The surge time is likely just how they measure it.
A current sensor will shut off as soon as it exceeds, whereas a temp sensor, which might be more accurate in terms of damage, can run longer at least initially.

I just took apart two 12v inverters, one 300 watt, one 150 watt, and they have essentially the same components, the 150 watt just didn't have a heat sink on the 12v transistors.
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Old 07-04-2021, 03:36 PM   #10
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I just took apart two 12v inverters, one 300 watt, one 150 watt, and they have essentially the same components, the 150 watt just didn't have a heat sink on the 12v transistors.
To be fair, those are some very small inverters, both HF. You're right design doesn't change between inverters of the same category all that much.


Inverter bottlenecks are usually cooling-related. Arbitrary draw cutoffs exist as a safety on top of thermal management solutions.
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Old 07-05-2021, 06:04 AM   #11
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Just like high amp fuse ratings with different shape curves over time

the only way to compare for a given use case between manufacturers is to test to destruction yourself.

The questiin really is a moot issue, for normal consumers, just stay within the continuous rating, any surges above for a second or two only.

If you push up to the limits, the unit won't last long.

High startup loads like air conditioners need slow start units added if running off inverters
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