PLC or BMS

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m sleem

Senior Member
Location
Cairo
I have designed a complete electrical system to supply and control no of desert coolers located above roof level of a ceramic factory. The reason of the control is to organize the operation between the coolers and exhausts according to the mechanical scenarios per zones. We recommended the PLC rather than the BMS due to the industrial application where the PLC is recommended & the other main reason is due to the cost since the BMS is expensive than the PLC, the problem came when the bidders quoted $120,000 for the system, when i saw this i requested the bidders to provide the drawings and the quantities in item wise not in lumps. Could you evaluate the PLC price where the no of desert coolers #164 & no of fans #45 & all of the system supplied by #8 power panels?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
there is no way to evaluate pricing based on the very sparse information you provided.

in general though you can probably look at how many digital and analog I/O there are and get a good feel.

figure $50 for each digital I/O point and $500 for each analog I/O point required. that should cover hardware and engineering time.

that will get you in the general vicinity of what it will cost.

to me, $120,000 for a job of this scale does not seem very far off.

there is a lot of engineering work involved in these kind of things such as drawing, PLC programming, and HMI configuration. Then there is the testing and startup. It is not unusual for the engineering time to far exceed the hardware cost.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
But if a system consists primarily of 100 identical subsystems I would think that there would be economies of scale on the design side if not in the hardware cost.
Testing and wiring time may scale directly though.

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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
But if a system consists primarily of 100 identical subsystems I would think that there would be economies of scale on the design side if not in the hardware cost.
Testing and wiring time may scale directly though.

Sent from my XT1080 using Tapatalk

It does not make all that much difference engineering time wise if they are exactly identical or just close to being identical. the drawings are mostly comprised of drawing files that are plopped into place and then edited. it sometimes takes me as long to edit the title blocks for each set as it does to make the other drawing changes.

A lot depends on the quality and consistency of the information given to the guy doing the PLC work. It is not unusual for us to get a drawing set in to quote against that has hundreds of errors in it. You can get some really screwy tag number schemes that make it difficult to work with.
 

m sleem

Senior Member
Location
Cairo
I have designed a complete electrical system to supply and control no of desert coolers located above roof level of a ceramic factory. The reason of the control is to organize the operation between the coolers and exhausts according to the mechanical scenarios per zones. We recommended the PLC rather than the BMS due to the industrial application where the PLC is recommended & the other main reason is due to the cost since the BMS is expensive than the PLC, the problem came when the bidders quoted $120,000 for the system, when i saw this i requested the bidders to provide the drawings and the quantities in item wise not in lumps. Could you evaluate the PLC price where the no of desert coolers #164 & no of fans #45 & all of the system supplied by #8 power panels?
My apologize when i said the PLC is cheaper in such applications than the BMS, i searched through internet & found that in the most cases the BMS is cheaper, but still the PLC is the most appropriate for the industrial applications.
One another question, how can i decide the no of analoge and digital I/O points?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I have never seen a BMS that is less expensive than a comparable PLC. What a BMS has going for it is a lot of canned control algorithms.

You figure out how many I/O there are by counting them. Get the P&ID out and mark the devices that have some kind of I/O with a high lighter. I use a different color for each type of I/O. Sometimes a device will have multiple types of I/O and even multiple I/O points of the same time.

Than just add them up.
 
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