What you are going to compare
Suppose you want to improve your existing BMS, and replace it with a new proprietary BMS. What additional requirements do you have, and how are you going to incorporate them?
Obviously, in the course of time, customers have expressed wishes. It is wise to include that feedback in the requirements package. After all, the new system must be able to last another 10 to 15 years.
So the new system must be able to handle all the tasks of the old system and also some new ones. Is it allowed to be more expensive? Does it have to be cheaper?
Features are difficult to express in terms of value, but this must be done nonetheless.
A possible calculation is to make an estimate of the turnover per feature over a period of 5 years. With or without that feature.
In doing so, look in particular at the emergence or the ability to parry competition.
Divide the turnover difference by the total production number and take the profit share.
Value = (turnover difference x profit %) / number
Purchasing price and work
When replacing the BMS with, for example, a custom BMS with embedded electronics (all electronics as far as possible on one board), a lot is going to change. Now it is important to calculate the two situations very well.
Do not forget in the price
- the mounting in the battery
- the external parts
- the stock parts
- the assembly time of the whole system
- the testing possibility (also after assembly)
- the purchasing time and stock management per part
Every technician who enjoys his project tends to estimate the work and costs rosy.
After all, a BMS may well be bought in the Far East for € 15.
But don’t expect him to put it in your battery himself and then specify 10 years of service life!
Then the question arises, what do you expect? Does your battery always work at 20 to 25 °C, or from -20 to +70? Is the humidity never above 80%? Are there no vibrations or shocks?
Oh yes, and how many times a year is a breakdown allowed? The price of electronics is made up of the price of the components that are on the printed circuit board, the circuit board plus the purchase and assembly of this.
Then comes programming, testing and adjusting, the warranty and, if you have a question, the support.
“Those aren’t pitfalls so far, are they?” No, they are not. This is a description of what you have to do to make a comparison.
The pitfalls are:
- Hardly anyone actually makes an objective comparison!
- Nobody does it like this, because it’s difficult.
- Everyone has their own preferences that they stick to!
It may sound simple, but an objective view can sometimes be enlightening.
See also our example of a good BMS for lithium batteries.
A short telephone call will tell you a lot more.