Missing the Forest for the Trees
With VA, Your Point of View is Everything
My name is Kazuo Akiyama, and I will be your "time-travelling" guide for today.
Kio mite morio mizu : To miss the forest for the trees
A metaphor for being so caught up in the finer details of something that you fail to appreciate its substance or overall significance.
Daijirin, 3rd Edition
Cost-cutting has always been an important theme in business. In the manufacturing industry, cost-cutting activities are referred to as "Value Analysis" (VA) and "Value Engineering" (VE). While the terms VA and VE are often used interchangeably, strictly speaking, they are different. Conceptually, value analysis and value engineering are both performed with the aim of maximizing value to the client, and therefore can involve not only cost-cutting but also the addition of value. In practice, however, when our clients tell us to "VA" something, what they really mean is "shut up and cut costs". Readers who would like to know more can Google "value analysis" or "value engineering" for more information.
Today’s story is about a problem I encountered in the past when performing value analysis. Stuck in the mindset that VA just meant eliminating excess, I took things too far. Like last time, I will be taking you 30 years back in time.
The Heyday of VA/VE
When I joined Kikusui, Japan’s electronics industry was booming, true to the title of best-selling book Japan as Number One. Electronics manufacturers also implemented extensive cost-cutting, in other words, value analysis and value engineering, in order to further boost performance. Everyone was gripped by the cost-cutting craze, and not only would manufacturers stop at nothing to cut costs, it was not unusual for clients to suggest modifications either.
At the time, I worked in OEM power supplies. One day we received a request from a client to cut costs on a device we supplied it with. A meeting was held in the client’s offices. Having received the client’s demands, we kicked off the meeting armed with the circuit diagram and configuration diagram for the OEM power supply.
The client made a range of demands. For example, they asked that the power capacity of the 12-volt positive supply be reduced from 4 amps to 3 amps to enable the reduction of the current ratings of the rectifying diodes and electrolytic capacitors used, representing a cost saving of x yen.
The client also asked that the power capacity of the respective outputs be reduced so that they just meet specification plus margin, thereby reducing the total output of the DC/DC converter and enabling the use of a switching transformer with a smaller core, representing a cost saving of x yen.
In terms of physical configuration, the client asked that the unit be redesigned to enable it to be connected directly to the load (the client’s device), thereby improving heat dissipation and allowing a thinner heatsink to be used on the OEM power supply. They also asked that all components be integrated into a single unit, to enable the elimination of the cooling fan fitted to the OEM power supply.
And so it went on. We ultimately agreed to go along with most of the client’s requests.
Inrush Current Limiter
One of the matters for consideration was the circuit to limit inrush current, the topic of this article. Let me briefly explain how a circuit to limit inrush current works.
The OEM power supply utilized a capacitor-input full-wave rectifier. The charging current that flowed through the electrolytic capacitor when the circuit is turned on was large enough to potentially blow the fuse or cause the switch contacts to weld together. In order to prevent this, an inrush current limiter was used to tame the inrush current (Figure 1). Note the resistor and relay in the center of the circuit diagram.
The circuit works in the following way:
- (1) When the power supply is powered up, the resistor limits inrush current.
- (2) After a set period of time, the relay is triggered.
- (3) The activation of the relay causes the second wave of inrush current to flow through the circuit.
(Providing that the electrolytic capacitor is sufficiently charged, the second wave of inrush current will be of moderate amplitude.)
Let us return to the VA/VE meeting in the client’s meeting room. The client told us that the OEM power supply was going to be incorporated into a minicomputer, which would usually be left on all day. They asked us to cut costs by reducing the resistor’s power rating, on the grounds that the circuit would not be turned on and off frequently.
I modified the specification in accordance with the client’s instructions.
Two months later, we delivered the client five OEM power supplies that incorporated the VA/VE cost-cutting measures. Sometime later, however, we got a call from the client saying that nothing happened when they turned on the power. We immediately visited the client site to investigate the problem. We found that the fault was caused by the resistor in the inrush current limiting circuit burning out. When the resistor failed, no current flowed to the capacitor, which meant that DC/DC converter did not function. Hence no power was output by the power supply.
So why had the resistor failed? It turned out that the power supplies were actually being turned on and off relatively frequently on the minicomputer production line. We determined that the resistors’ insufficiently high-power rating had caused them to burn out and fail. In the meeting to discuss VA/VE, the clients had told us that the minicomputers would only be turned on once or twice a day, and said that as current would only flow through the resistor to limit inrush current for that split second, we could use a resistor with a low current rating. However, this was only true of the time the device was actually in use and did not take into account testing performed during manufacture, something we had overlooked. As a stopgap measure, we replaced the burnt-out resistors with components of the originally specified rating. Power resistors are large, so it was a tricky task. While we had acted in an effort to implement the changes requested by the client, I became painfully aware that we had not given sufficient consideration to the matter.
With VA, Your Point of View is Everything
As I mentioned at the beginning of this article, the purpose of VA is supposed to be the maximization of value for the client (the balancing of costs against results). While we engineers leave no stone unturned looking for opportunities to cut costs as we tweak designs, the more you get caught up in the details, the more short-sighted you can become, causing you to forget why you decided on the original specifications in the first place. You then end up removing an essential part of the circuit, causing the circuit to become unbalanced. This is exactly what happened in my case.
Toes are an interesting analogy. Toes make up a very small part of our bodies, and you would be forgiven for thinking that we would get on fine without them. After all, we hardly ever use our toes. If anything, toes can be a nuisance, causing us pain every time we stub them on the corner of a chest of drawers. However, people who lose their toes as a result of frostbite have trouble walking in a straight line. Toes in fact play an important role in balance.
Clients will always ask you to cut costs. However, I urge you not to take a short-sighted perspective to cost-cutting like I did. Whatever you do, make sure you don’t cut off your toes to spite your face.
Solutions Development Division, Solutions Development Department (Supervisor)
[Major achievements in product development]
PAK-T, TAK-A, PAD-LET series regulated DC power supplies
PAX and PBX series high-speed programmable power supplies
PFX40W-08 battery charging and discharging tester