Lenco VS Bennett actuators

[Wakeman22]

Looking to do the DIY surf gate or tabs. Looking at the Bennet or Lenco systems. Would like to know the difference in each with plusses and minusses of each. Looking at the electric style actuators over hydrolic.

[Germaine Marine]

Looking to do the DIY surf gate or tabs. Looking at the Bennet or Lenco systems. Would like to know the difference in each with plusses and minusses of each. Looking at the electric style actuators over hydrolic.

Bennetts aren't going to give you near the versatility you will need. The main plusses with lencos is the ease in which they operate as well as replace if necessary. IMO its the only option I would go if doing a surf tab setup. You could spend some big bucks and go a Parker actuator route which is electric over hydraulic. The main issue with those is the footprint and the power needed to run them and also the cost.

1. lenco
2. Parker

No on Bennetts.

[IDBoating]

Lencos are the "standard" though they've had some QC issues in the recent past.

(Electric) Bennetts are just as powerful as Lencos, but have different options which may or may not suit your needs. Their amperage behavior is roughly the same (trust me, I've characterized both in great detail). Hint: Startup current can spike over 70 amps!

The Parker units are more expensive and more technically complex. There's nothing inherently magical about having hydraulics in the middle of the system when they're ultimately being driven by electrical power anyway. What the Parker units DO bring to the table, which (for some unfathomable reason) neither the Lencos nor the Bennetts seem to be willing to bother with, is an optional position sensor. If you want to go electric AND want positive feedback on position integrated into your actuator, Parkers are the only choice AFAIK.

The really weird part of that is Bennett DOES offer a position sensor in their hydraulic actuators (such as were used on Tige's TAPS2 center tabs like the one on my 2009 24Ve). So Bennett, at least, certainly knows 1) the value of having position sensors in linear actuators, and 2) how to put sensors in their actuators. But they just can't be bothered to do it in their electrics. Weird, weird, weird.

[IDBoating]

Sorry, the way I wrote that implied it was just Bennetts that have the inrush current spike. It's actually BOTH Lenco and Bennett, and indeed all electric actuators (there's a third brand out there we've taken a cursory glance at but never thoroughly characterized).

The nature of electric actuators is such that they will always have a huge inrush current. This is not "broken", it's just the nature of the beast. If you want to get a bit more technical: Electric actuators have at their heart an electric motor. When you first apply current, the motor is not turning so its coils appear as nearly a dead short, allowing much more current to flow than their "rating" would suggest. As the motor then begins to turn, an inverse current known as "back electromotive force" (or "back EMF") begins to build. Essentially the motor becomes a little generator (a motor in reverse), because its coils are passing through a magnetic field - exactly how a generator works. It may seen counter-intuitive that a motor would generate current, but back EMF is very real and as it increases, it works like backpressure on the input current. Eventually the motor speed increases enough, and the back EMF increases enough, to limit the input current and the motor behavior stabilizes. (If this weren't true, an unloaded motor would spin faster until it tore itself apart mechanically.)

To go a bit deeper into the weeds, this is a scope shot of the current behavior of an electric actuator from back in 2015:

ACS723AndCurrentProbe.png

Here we were comparing the behavior of a current sensing circuit we designed (yellow trace) to an actual current probe (blue trace). Each major vertical division indicates 10 amps of current. So in this test, you can see that when power was applied, the current shot up to almost 50 amps in under one millisecond. The little spikes on the traces show when motor poles rotated past their brushes; you can see the spikes becoming more frequent as the motor gains speed. You can also see the average current dropping as the motor gains speed, due to back EMF as described above. At the far right of the display, which is 65-70 milliseconds after powerup, the current is down to ~20 amps and still headed lower toward its eventual average of around 7 amps continuous (not visible).

Note that everything you see on the display happened in the first tenth of a second after current was applied to the actuator. This is why actuators don't blow fuses every time... standard slow blow fuses tolerate inrush current as long as it doesn't sustain for too long. However, electronics must accommodate this current because it is very real. That's why I originally said "Hint: Startup current can spike over 70 amps!" While fuses may tolerate it, semiconductor devices or relays or switches or whatever cannot just casually ignore it. There really ARE current spikes happening in the many tens of amps and if you ignore that, something bad could happen.

Hope this was interesting, sorry for the distraction if not.

[freeheel4life]

IDboating, not to derail the convo and continue handing out the lesson, but I've heard starters work in the same way. In that a slow cranking starter can actually burn up because it can't create enough back EMF and that inrush current stays high instead of being only momentary( and 1/0 cables with large amperage maxi fuses). Just curious if thats a valid theory in your professional opinion??

[IDBoating]

A motor is a motor, so yes - that's valid. If you hold a motor's stator so that it cannot rotate, the motor has almost zero resistance to current flow so you'll get massive current. Allow it to spin up to speed and the back EMF causes the current to settle to its nominal value. Imagine plotting a curve of current flow between those two points and you can see that as you approach "motionless" the current will go way up - and if you hold it there, anything that cannot take sustained high current will be affected. "Affected" in this case could include fuses or fusible links burning through, motor windings melting their insulation and thus self-shorting (which leads to more localized heating/melting and thus a chain reaction that destroys the entire winding), cables getting hot enough to melt their insulation, connections (which are naturally higher resistance nodes anyway) overheating, etc.

BTW, "inrush" is usually used to indicate a momentary condition. That's appropriate for a normal motor startup. But in the example you cite, where the rotation is held at abnormally low RPM's for a while, "inrush" sort of loses its meaning because now you're talking about a sustained condition. I guess you could say that the system can tolerate inrush current, but sustained currents at those same levels is likely to be destructive. More generally, most systems (whether electrical, mechanical, or whatever) can tolerate "peak" values for a short time but those same values over a longer time cause problems; otherwise they wouldn't be spec'd as "peak" values! {grin}

EDIT: This is true of semiconductors too, which is why transistors "burn out" when subjected to excessively high currents for too long. The die can tolerate intermittent peaks but sustained operation outside what is called the "Safe Operating Area" will damage or destroy the die. And repeated operation outside the SOA can lead to progressive damage, weakening the device and leading to failure later even at a lower, normally acceptable operational level. The semiconductor industry publishes very clear specifications of what "intermittent" and "SOA" means for individual products, a pattern NOT followed by other disciplines which is very annoying because right at the moment I'm trying to determine what "intermittent" means in a mechanical environment and nobody seems to know.

[freeheel4life]

Thanks as always for the lesson ID.

[IDBoating]

Not a "lesson", just friends talking shop! {grin}

[Wakeman22]

No, this is a lesson. And thanks for the reply back to the original question. IDBoating i was hoping you would chime in. I am considering on the options on which way to go. The Bennetts had a little bit of interest because of the adjustability and their feedback system that they have for adjustment. However I do understand that the lencos have a little bit more power and seem to last a while longer. I am still on the fence trying to decide to go with tabs or Gates. I do plan on using an electronic controller to help automate whichever way I do go with. Having the 24ve with the characteristic that it needs that back corner on the Surfside stuck in the water may dictate that Tabs are a must. However with the listed boat and a suck gate the wave is much better. With tests on the suck gate the 24ve still needed list to the surf side. I did play around with ballast weight and placement but still came to the conclusion that listed and corner heavy produced the best wave. But I still want to do transfers without buying a new boat.