# Designing an EV charger

Thread Starter

#### ElectricLearner

Joined Feb 22, 2023
3
Hi,

I'm quite new to Power Electronics but am trying to expand my knowledge of the subject and trying out some projects. I'm currently trying to model an EV charger on MATLAB but first need to size the components. I'm trying to come up with a design spec to size the components for my DC-DC converter but can't seem to find anywhere that tells me what the maximum allowable ripple current and ripple voltage is for charging a battery or even what the nominal charging voltage or current should be. I would need these to size my LC filter bit of the DC-DC converter.. Is there an engineering recommendation/standard that specifies these type of things?

Many thanks in advance for your time and help!

#### MrSalts

Joined Apr 2, 2020
2,767
Hi,

I'm quite new to Power Electronics but am trying to expand my knowledge of the subject and trying out some projects. I'm currently trying to model an EV charger on MATLAB but first need to size the components. I'm trying to come up with a design spec to size the components for my DC-DC converter but can't seem to find anywhere that tells me what the maximum allowable ripple current and ripple voltage is for charging a battery or even what the nominal charging voltage or current should be. I would need these to size my LC filter bit of the DC-DC converter.. Is there an engineering recommendation/standard that specifies these type of things?

Many thanks in advance for your time and help!
Standards for EV chargers exist.
You may have to pay for a copy of the standard from SAE or ISO.
If this is just for fun, you can just make an assumption of 5 volts of ripple or what ever random number you want to pick.

#### crutschow

Joined Mar 14, 2008
32,026
Batteries are very tolerate of ripple in their charging current.

The charging voltage and current is determined by the battery your are charging, which is given in the specific battery specs.

Thread Starter

#### ElectricLearner

Joined Feb 22, 2023
3
Batteries are very tolerate of ripple in their charging current.

The charging voltage and current is determined by the battery your are charging, which is given in the specific battery specs.
Thanks for your answer. That makes sense but I do wonder though how EV chargers for public use are designed? Like the ones in fuel stations or public roads for general public use. These would have different types of EVs plugged into them with a different charging voltage and current specification right? How does the charger generally determine the charging voltage and current in that case if you know?

Thread Starter

#### ElectricLearner

Joined Feb 22, 2023
3

#### MrSalts

Joined Apr 2, 2020
2,767
Thanks for your help! Those seem quite expensive for my budget to be honest. I only really need to find out the general ripple voltage/current recommendations. Do you know anywhere that maybe refers to this section of the standard maybe?
I think 5-10v is a good place to start. Don't let that stop your work. You can always adjust component values once you learn the right answer. The rest of your design will be the same. A $175 isn't so much. You'll spend more on that for a safe enclosure, not to mention the thousands for the multi-kilowatt transformer and possibly a new electric service box for 480VAC power. Chargers are not a cheap diy project - unless you want a little 115VAC project but even that will be way more than$175.

#### argile_tile

Joined Feb 24, 2023
9
Remember design of the charger is the least of worries. Physical fixtures (ie connectors) are probably not found in Walmart. And remote electrical installation: probably illegal unless your an electrician (it requires separate equations and hardware).

I think every country already has "a few" charging station makers / companies. They of course get political money then call it "a private company" if I am not correct.

#### argile_tile

Joined Feb 24, 2023
9
Making a min-charger will be easier since the total power will always be low - the battery will hardly care either way. However EV batteries are huge. There's definitely a risk you walk away, fall asleep, and a serious fire results. I don't see where they pay-off of the project is. (ie, my angle on this is: hobbists are discouraged from "repairing microwaves" for a reason)

#### GetDeviceInfo

Joined Jun 7, 2009
2,142
The EV chargers I’ve been working with deliver a charge current in direct response to a CANbus command issued by the BMS.

#### Juhahoo

Joined Jun 3, 2019
300
Lets be honest and straight, electronics is engineering where you have a gentle learning curve. You advance from simple circuits to more advanced. Your project sounds a one that requires years of experience from demanding electronics and is not for beginners. You may use some time for exploring but to be able to build an actual ptototype doesnt come by running simulations only, you need to build, iterate, learn, burn some parts and iterate more, it all takes time, money and dedication.
Not knowing enough your background I would make something more simple, like a simple charger for a bike, or a car battery, study and explore it and then go further.

#### Ian0

Joined Aug 7, 2020
7,441
Batteries are very tolerate of ripple in their charging current.
Whilst we all know that this is true, there are some really pedantic BMS out there, which will shut everything down at the first whiff of ripple voltage.

#### MisterBill2

Joined Jan 23, 2018
14,666
What sort of EV do you want to charge?? The public charge stations do, as already mentioned, converse with the vehicle battery system to know what voltage to supply, which mostly seems to be 400 or 800 volts, at a whole lot of amps. So we are talking big power and a fair level of hazard, and besides that you must be certain the communication is correct. So not one part of it is simple.

#### DickCappels

Joined Aug 21, 2008
9,853
Lets be honest and straight, electronics is engineering where you have a gentle learning curve. You advance from simple circuits to more advanced. Your project sounds a one that requires years of experience from demanding electronics and is not for beginners. You may use some time for exploring but to be able to build an actual ptototype doesnt come by running simulations only, you need to build, iterate, learn, burn some parts and iterate more, it all takes time, money and dedication.
Not knowing enough your background I would make something more simple, like a simple charger for a bike, or a car battery, study and explore it and then go further.
To that I would add that in the case of power supply design one should expect to burn one’s fingers occasionally and be prepared to replace lots of expensive parts if not because of failures then because they need to be replaced to fine-tune the design. Once much power is involved, it is an expensive (and sometimes painful) process.

#### Ian0

Joined Aug 7, 2020
7,441
If you want to make a car charger, why not start with the AC version, which is good for 23kW in its three-phase form?
All you need is the connector (which you can get from AliExpress), and contactor which is operated by the pilot contact, then a 555 to send the right pulse width at 1kHz (if I remember correctly - you’d better check) to tell the car the maximum current it can take from the charger.
DC chargers start at 50kW (say 400V @ 125A), which is going to require some considerable expenditure in transformers and semiconductors!

#### MisterBill2

Joined Jan 23, 2018
14,666
The very first thing is a common beginners mistake, that unfortunately repeats with non-beginners as well.
Prior to starting any design of almost anything, it is very useful to determine a set of requirements for what is to be designed.
That is applicable to a charging system or a wheel-chock, and almost everything else.
We have not been given even one word relative to any requirement or specification by the thread starter, other than a comment that some varieties seem rather expensive.
Without a set of requirements an actual design is a waste of time and effort.