# Schneider Altistart 48



## pudge565 (Dec 8, 2007)

Bump with details I forgot. The motor is running a blower fan which is above the motor driven by belts. The genset is an ex military set 100 KW.


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## JRaef (Mar 23, 2009)

pudge565 said:


> .. The nameplate is 96.4A start up current is about 160a.


Soft starters were my life for 20 years and I have seen this sort of thing countless times. This is most likely a case of someone seeing that the current limit setting CAN be set that low, so they think it will still work, when in fact it NEVER will. When I worked designing soft starters, we never allowed a current limit setting below 200% of FLC because of that. Competitors (Telemeccaneccalika being one of them) however, in a weird attempt to try to make theirs look "better", would allow setting theirs lower, some as low as 50% of motor FLC, even though their engineers should KNOW that any setting below 200% will only work on a motor that is uncoupled from ANY load. It's one of those decisions obviously made by marketing people, not engineers. Unfortunately, 99% of users don't have the time to learn these sort of details in advance, most people in the industry see only one or two soft starters in their LIFETIME. So in a way, I always though it was irresponsible to do that. Nonetheless it's very common now, because when one did it and specs were written requiring that, others felt compelled to follow. OK, enough ranting.

The ATS48 is NOT one of the best soft starters on the market, so it will shut itself down to protect itself if you stress it too much. Still, if the peak current never gets above 160A I doubt that is the case here. Either something is seriously wrong with your readings, or someone is attempting to do something with the soft starter that violates the laws of physics. That is only 164% of FLC and even an uncoupled motor will not likely start with a current setting that low. A squirrel cage centrifugal blower*, with the dampers closed, MIGHT be able to accelerate with 250% current, but more likely 300-350%. If the dampers are wide open it may not accelerate at all without tripping on OL, but certainly no less than 450-500% current. But that generator will never deliver that, it's too small. This is often counter intuitive to people unfamiliar with centrifugal machines, so this happens a lot by the way.

What YOU need to do FIRST is to make sure they are not trying to accelerate with the dampers wide open. In a centrifugal* blower, Load = Flow, so if you want to start with as little load as possible, you want as little flow as possible. Next then is to set the Current Limit as high as you can without causing too much VD on that little generator. That is a little too small for a 40HP motor, but it should be able to be made to work. I would start off with 300% Current Limit and look at the VD. If it drops more than 10%, lower it again 25%, if less that 10%, try raising it by 25%. Once it stays at or below 10%, stop there and see if it accelerates without tripping on OL. If not, shorten the Ramp Time as low as possible,. The concept here is that when you have a severe power supply limitation, as you do in this case, you can no longer waste ANY of the thermal time of the motor in ramping, you need to begin accelerating immediately and as fas as you can with everything you can get from the generator. 

So this will be a trial-and-error session, no way around it (unless someone has some VERY expensive Transient Motor Starting analysis software, like SKM Power Tools, that can predict the effects in advance. SKMPT is about $15K. Something like this is not worth it if you don't already have it). Remember though that when testing, you have to be aware of the number of starts per hour you are subjecting that motor to and you have to count them all, successful or not. Something like this, where you have to experiment, can often take all day because of having to wait between starts, otherwise you risk smoking the motor insulation and buying someone a new motor.

*I am assuming this is a centrifugal blower, like a fan or squirrel cage blower, not a high pressure lobe blower like a Roots blower. If it is one of those, do NOT choke off the flow as it will pull a vacuum and damage something. It will also NEVER start with that small generator no matter what.


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## Mulder (Sep 11, 2010)

^ Stuff like this is why I love this site. Great post Jraef!


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## pudge565 (Dec 8, 2007)

JRaef said:


> Soft starters were my life for 20 years and I have seen this sort of thing countless times. This is most likely a case of someone seeing that the current limit setting CAN be set that low, so they think it will still work, when in fact it NEVER will. When I worked designing soft starters, we never allowed a current limit setting below 200% of FLC because of that. Competitors (Telemeccaneccalika being one of them) however, in a weird attempt to try to make theirs look "better", would allow setting theirs lower, some as low as 50% of motor FLC, even though their engineers should KNOW that any setting below 200% will only work on a motor that is uncoupled from ANY load. It's one of those decisions obviously made by marketing people, not engineers. Unfortunately, 99% of users don't have the time to learn these sort of details in advance, most people in the industry see only one or two soft starters in their LIFETIME. So in a way, I always though it was irresponsible to do that. Nonetheless it's very common now, because when one did it and specs were written requiring that, others felt compelled to follow. OK, enough ranting.
> 
> The ATS48 is NOT one of the best soft starters on the market, so it will shut itself down to protect itself if you stress it too much. Still, if the peak current never gets above 160A I doubt that is the case here. Either something is seriously wrong with your readings, or someone is attempting to do something with the soft starter that violates the laws of physics. That is only 164% of FLC and even an uncoupled motor will not likely start with a current setting that low. A squirrel cage centrifugal blower*, with the dampers closed, MIGHT be able to accelerate with 250% current, but more likely 300-350%. If the dampers are wide open it may not accelerate at all without tripping on OL, but certainly no less than 450-500% current. But that generator will never deliver that, it's too small. This is often counter intuitive to people unfamiliar with centrifugal machines, so this happens a lot by the way.
> 
> ...


So if I understand you right you are saying to turn ln up to at least 150% of name plate and turn acc time down as low as possible. Does torque setting need to be changed at all?

The company told this guy the gen set would be big enough to run it. According to him it was test run that shows on the screen (not sure what the screen is).

The drive always says rdy even after trip out but there is a light on the board in another cabinet that says motor overloads and lights uo.


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## JRaef (Mar 23, 2009)

pudge565 said:


> So if I understand you right you are saying to turn ln up to at least 150% of name plate and turn acc time down as low as possible. Does torque setting need to be changed at all?
> 
> The company told this guy the gen set would be big enough to run it. According to him it was test run that shows on the screen (not sure what the screen is).
> 
> The drive always says rdy even after trip out but there is a light on the board in another cabinet that says motor overloads and lights uo.


Not 150%, you are already at 164%. I'd say 250% minimum, but I would start at 300-350% if the generator can handle it.

People lie about "test runs" all the time.


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## pudge565 (Dec 8, 2007)

JRaef said:


> Not 150%, you are already at 164%. I'd say 250% minimum, but I would start at 300-350% if the generator can handle it.
> 
> People lie about "test runs" all the time.


Ok thanks for the help, I will try that and take a volt measurement on start up.

ETA: I also told him to take the belts off and see if it will start with no load on it.


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## pudge565 (Dec 8, 2007)

JRaef said:


> Not 150%, you are already at 164%. I'd say 250% minimum, but I would start at 300-350% if the generator can handle it.
> 
> People lie about "test runs" all the time.


Just to be clear which setting needs to be adjusted? According to this PDF it seems the OL Is already set at 476%


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## JRaef (Mar 23, 2009)

Not sure where you are getting 476% from that. That is just showing you what the factory default programming is, not what someone has set it for in commissioning. The Overload setting should be set for the motor nameplate FLC. The Current Limit setting is separate.


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## pudge565 (Dec 8, 2007)

JRaef said:


> Not sure where you are getting 476% from that. That is just showing you what the factory default programming is, not what someone has set it for in commissioning. The Overload setting should be set for the motor nameplate FLC. The Current Limit setting is separate.


Ok so Ln is what does the OL setting, and the ILt is totally separate? I was thinking the Ilt was the OL setting, which is set to 472%. Now we are on the same page, this is why I am going to school for this type of thing, I've no knowledge of soft starts, VFDs, or PLCs.


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