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Clarifying 'on board charger'

8K views 93 replies 18 participants last post by  dk6780 
#1 · (Edited)
Edited for correction

Wanted to know why an onboard charger was required. It's now been answered as below.

Home charging is always AC.

All EVs have an onboard charger which takes AC (usually provided via a Type 2 plug) and converts that to DC internally to charge the battery. Most models can only take a single-phase 7kW AC charge (occasionally less), but some take 3-phase AC at higher power levels including 22kW and more. Most home chargers can't deliver more than 7kW as most UK homes don't have 3-phase supplies.

Many EVs can also take a DC connection, direct to the battery, for DC Rapid Charging which is provided by public chargers via CCS or CHaDeMo connectors. In this case it's the public charger's job to convert the mains AC to DC at high power levels, and manage the charging.
Public charge points for EV's use direct current (DC) and AC (alternating current).

EV batteries use DC.

Outlets such as those in homes use AC, so the car has to have an onboard AC to DC converter/charger box. These are often less powerful such as 22kw, whereas public chargers can connect direct to battery, bypassing onboard charger and then charging faster.
 
#2 ·
Public charge points for EV's use direct current (DC), rather than AC (alternating current).
That's not true. High power rapids (Chademo and CCS) are DC, others rapids may be 43 kW AC for cars that use that. Most other public points will be 7 or 3.5 kW AC which are the same as home outlets and those use the car's on-board charger. As you say, the latter will have a power limit.
 
#3 ·
Just wanted to clarify if the following is correct:

Public charge points for EV's use direct current (DC), rather than AC (alternating current). EV batteries use DC.
However, outlets, such as those in homes use AC, so the car has to have an onboard AC to DC converter/charger box.

The onboard charger on all BEVs and plug in chargers had to provide an AC to DC conversion as you state but had other important functions such as providing the correct voltage and controlling the charging rate. The AC Input rating of the onboard charger could be anything from 2.5kW to 43kW depending on the model of car.

But onboard chargers often can only convert up to 11 or 7kw.

Let me know if I got anything wrong, thanks.

Literally everything in this post is incorrect.

Vast majority of public charge points provide single phase or three phase AC.

SOME public charge points, normally known as Rapid chargers, provide DC.
 
#4 ·
However, outlets, such as those in homes use AC, so the car has to have an onboard AC to DC converter/charger box.

But onboard chargers often can only convert up to 11 or 7kw.
Does it matter if the onboard charger can only convert at a rate of 11 or 7 (or even 3.6) kW - if you plug in when you get home in the evening, you will have a fully charged battery by the next morning.

There are two 'modes' of charging - destination charging when the car is charging while you are doing something else, and en-route charging when you are waiting for the car to charge so you can get on with your journey.

For destination charging, providing you can get enough charge for your next journey while you are at the destination, the actual charging rate does not matter.

For en-route charging, you would like to charge as quickly as possible so that you can be on your way, so the 'Rapid' chargers that feed DC direct to your battery are the ones to go for.
 
#26 ·
Does it matter if the onboard charger can only convert at a rate of 11 or 7 (or even 3.6) kW - if you plug in when you get home in the evening, you will have a fully charged battery by the next morning.
There are two 'modes' of charging - destination charging when the car is charging while you are doing something else, and en-route charging when you are waiting for the car to charge so you can get on with your journey.

For destination charging, providing you can get enough charge for your next journey while you are at the destination, the actual charging rate does not matter.

For en-route charging, you would like to charge as quickly as possible so that you can be on your way, so the 'Rapid' chargers that feed DC direct to your battery are the ones to go for.
There are two 'modes' of charging - destination charging when the car is charging while you are doing something else, and en-route charging when you are waiting for the car to charge so you can get on with your journey.

For destination charging, providing you can get enough charge for your next journey while you are at the destination, the actual charging rate does not matter.

For en-route charging, you would like to charge as quickly as possible so that you can be on your way, so the 'Rapid' chargers that feed DC direct to your battery are the ones to go for.
 
#8 ·
Your original post was pretty much correct, but people have jumped on it because of the suggestion that public charging is always DC, when you can obviously get public AC chargers as well as DC. Home charging is always AC.

All EVs have an onboard charger which takes AC (usually provided via a Type 2 plug) and converts that to DC internally to charge the battery. Most models can only take a single-phase 7kW AC charge (occasionally less), but some take 3-phase AC at higher power levels including 22kW and more. Most home chargers can't deliver more than 7kW as most UK homes don't have 3-phase supplies.

Many EVs can also take a DC connection, direct to the battery, for DC Rapid Charging which is provided by public chargers via CCS or CHaDeMo connectors. In this case it's the public charger's job to convert the mains AC to DC at high power levels, and manage the charging.
 
#12 ·
Wanted to know why an onboard charger was required.
It is not 'required' but if you didn't have one you'd need a DC charger at home (assuming you wanted to charge at home).

The OBC is an AC->DC converter to make conventional mains suitable to charge a DC battery. There is no particular reason why that converter needs to live in your car rather than on your garage wall, but it is just the way this EV thing has evolved, with the only electrical supplies originally being your house, so it made sense to carry that converter around with the car in case you stopped somewhere else with AC only supply.

Personally, I think that is the way this will all go, and OBCs will be deleted for cost and weight benefits, but at the moment there is no industry/market for that.
 
#13 ·
I got a great idea. We could get the manufacturers to not fit any seats / seatbelts/ airbags for passengets. Just think of the weight and cost saving. The idea being that g&d forbid anyone would need them, just fit your own from your previous car. Same with wheels, just transfer them over. SatNavs arn't needed. Windows that open are an anachronism, ditch them. Let's keep going and get cars stripped down to what a buyer really needs!
 
#15 ·
I see the point @donald is making that long term (at least 5 years) AC charging might disappear or be a cost option.

It is far harder and expensive to do V2G with AC, so long term homes could have low power DC charging due to V2G requirements. The units are already getting cheaper and smaller as we see with the current trial.
 
#23 ·
I see the point @donald is making that long term (at least 5 years) AC charging might disappear or be a cost option.

It is far harder and expensive to do V2G with AC, so long term homes could have low power DC charging due to V2G requirements. The units are already getting cheaper and smaller as we see with the current trial.
The grid is AC, the battery DC. Not beyond the ingenuity of man to make it work.
 
#18 ·
Sorry to disagree with suggestion that home DC chargers will be the norm and onboard chargers will be dumped.

Already there are issues with comms compatibility between EVSEs and BEVs. Imagine the long winded process in terms of certification and actual compatibility, DC chargers to any BEV that would happen if DC home charging was to be the norm.

Not only that, but the acceptance threshold for adoption of BEVs would increase. Help us all if OLEV got involved in assigning minimum acceptable technical standards for their "approved" DC home chargers.

Thoroughly bad idea.

Safety: 400V DC trailing flexible cables subject to random domestic maintenance approach. Sorry, did I say thoroughly bad idea.
 
#19 ·
1

Maybe you have missed that 1000 homes in UK are getting DC chargers for V2G? They are being made by Indra and I am sure @Mike Schooling will confirm they are perfectly "safe"

 
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#20 ·
Yes, did certainly register before I made that post.

I have every confidence that Indra will manage quality of supply, installation, maintenance and possibly operation over the period of a TRIAL.

Not the same as mass market IMHO.

Any views from Indra themselves on what would be required long term?

Just conscious that at 400V (800V for some cars on the way) we have crossed over some basic physiological safety barriers. Certainly with Public DC charging, we expect that a level of maintenance is carried out by competent persons.
 
#38 ·
Yes, did certainly register before I made that post.

I have every confidence that Indra will manage quality of supply, installation, maintenance and possibly operation over the period of a TRIAL.

Not the same as mass market IMHO.

Any views from Indra themselves on what would be required long term?

Just conscious that at 400V (800V for some cars on the way) we have crossed over some basic physiological safety barriers. Certainly with Public DC charging, we expect that a level of maintenance is carried out by competent persons.
Sorry. Missed this thread.

So safety for DC at home (with the Indra V2G)...

-We are using the very mature CHAdeMO standard.

-High quality certified cables and connectors.

-No voltage in the cable until all checks are complete.

-Cable locked into position while charging.

-Insulation and isolation check of the cable during every charging initiation.

-Constant checking for DC leakage while in operation.

-Higher dielectric rating than AC chargers.

-Constant checking of circuit resistance while in operation.

-Dual galvanic isolation in the power electronics - we go from ac-dc-ac-dc when charging and dc-ac-dc-ac while discharging (cars generally have a single isolation barrier). This means there is no meaningful current path from DC to chassis ground or Earth. The only way you could get electrocuted by the charger is to somehow touch HV+ and HV- while the CHAdeMO protocol is satisfied everything is OK, even then the resistance check above kicks in.

-Much more monitoring within the charging point (which includes the power stage) which is web connected and monitored allowing us to see issues and trends.

- Charger itself can isolate the DC and or AC supply in/out of the charger if it senses a fault.

-Logging available do help learning should something go wrong.

-Insulation, Fire retardant, impact and mechanical shock rating of the enclosure hugely exceed regs.

-Emergency stop button just in case.

-------------

FWIW, i think we'll see DC charging become the norm (at home/on route/autonomous hub) with on board chargers reduced to granny lead spec to keep cost down.



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#53 ·
If v2g v2h, is easy to make worldwide, then i can see the ac charger decline, if not then to me it looks like an uphill battle to get dc chargers into houses. How big is the difference between the dc charger you use to an ac charger, partwise @Mike Schooling ?
Quite a lot. AC chargers are basically just a switch (relay/contactor) with some comms around it. The AC to DC bit is in the car.

With DC charging, the AC to DC bit is in the box on the wall.

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#51 ·
The issue for vehicles is cooling the (OBC) electronics which means hoses, radiators, pumps etc.

Not entirely convinced that cooling OBC, those greater than 3kW input power anyhow, is the big driver on the basis that a liquid cooling system, ie radiators and pumps, will be required anyhow for drive motors and the battery itself.
 
#52 ·
Yes but it adds to the complexity

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#66 ·
They would only do it once manufacturers offer to delete OBCs for saving a few thousand quid.
Why would they offer that big a discount when the cost saving to them is only a few hundred ?
A lamp post is a big thing and has no trouble air cooling a kW class lighting system.
Fit new ones with them build in.
As I said, you could design a purpose-made one, but it isn't practical to retrofit most existing ones - replacing a lamp column is way more expensive than replacing a cover with an AC EVSE.
You've managed to pick a real edge case there to really flog your dead-horse argument. If someone is living on a street with AC outlets, then they tell their dealer they want their car with the optional OBC.
It's a pretty significant number, by no means an edge case. There are plenty of other situations where size is a significant issue, but installation and maintainance cost is the real killer.
Let the market decide.
I'm sure it will.
Once battery supply gears up to the point where demand is satisfied and manufacturers are having to compete on price, we may see a few offering optional OBCs, but there is no way it will be a few thousand £ less.
 
#68 ·
Why would they offer that big a discount when the cost saving to them is only a few hundred ?
This is a fantasy.

"A thousand or two" would be closer I think.

ATM no vehicle manufacturer makes their own inverters, AFAIK, they buy them in. How could any 1st tier company design, engineer, homolgate and deliver an inverter to automotive standard if the raw parts alone come to a few to several hundred pounds?

We've had this situation before where people picture a few cheap low current Chinese devices off ebay. Power electronics is a big mass of complicated and expensive parts to make them fit for market and UL & IEC61000 compliant.

Ask Mike, if you don't believe me.
 
#78 ·
Just catching up with this very articulate post after bit of a break from the forum...

A couple of points I'd throw out there are:

A) There's a lot of talk of viability of lamppost charging - Does anyone know if the new LED lampposts that are being rolled out throughout the country actually have 230V AC going to them? When they were all replaced in our area, not only were they unhelpfully placed on the property edge of the pavement instead of the road edge, but they dug new trenches for every single one and laid all new cables, which makes me wonder if there's just a low voltage DC supply going to them these days.

B) With regard to the cost of hotels and businesses replacing their AC posts with DC posts, after working with my employer on potential charging solutions, half the battle is groundworks for getting supply to location most of the time. When the AC posts eventually fail, replacing them with DC alternatives should be a much simpler process I would have thought, as half the work is done.
 
#79 ·
Just catching up with this very articulate post after bit of a break from the forum...

A couple of points I'd throw out there are:

A) There's a lot of talk of viability of lamppost charging - Does anyone know if the new LED lampposts that are being rolled out throughout the country actually have 230V AC going to them? When they were all replaced in our area, not only were they unhelpfully placed on the property edge of the pavement instead of the road edge, but they dug new trenches for every single one and laid all new cables, which makes me wonder if there's just a low voltage DC supply going to them these days
I can't see much benefit in doing this except where there are space or other constraints in the column , though the lower draw of LEDs may mean they run lighter mains cable, limiting available power.
B) With regard to the cost of hotels and businesses replacing their AC posts with DC posts, after working with my employer on potential charging solutions, half the battle is groundworks for getting supply to location most of the time. When the AC posts eventually fail, replacing them with DC alternatives should be a much simpler process I would have thought, as half the work is done.
But the DC chargers would still be 5-10x more expensive, and significantly bigger than AC ones.
 
#81 ·
This thread is very useful. One (maybe simple) question @Mike Schooling. Why is your V2G charger DC output to car rather than using the car's AC-DC inverter ? Thanks.
By AC-DC inverter do you mean the on board charger (strictly speaking this is a converter)?

The OBC is a one way device. DC (CHAdeMO) gives us direct access to the battery and the bidirectional power electronics can then go in a box on the wall.

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#87 ·
It's possible but not standardised.

The body behind it are frustratingly slow and shortsighted when compared to say the CHAdeMO association.

Also very poorly defined which leads to compatibility issues (look a look at ipace and etron ccs on ecotricity network issues when first launched).

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#86 ·
There's an interesting debate to be had over the efficiency of mounting the AC to DC converter on the car or on the wall. At present I have this expensive item on my car and can utilise it both at home and at work, places where no-one else charges. If it were to be on the wall it would require two of them, although there would be a minor gain in efficiency of not carrying the mass around. There would be a massive benefit if V2G were cost effective (the economics don't work for me currently) or I shared a charge point (when the cost would be shared across multiple users). I cannot see either of those happening for me in the near future, but at some point manufacturers may offer AC coupling only as an expensive option once the need for a more balanced infrastructure has been met with V2G widely distributed.
 
#88 ·
precisely. i suspect most cars will be dc only and ac becomes either very low powered or a costed option

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