Ingineer said:
valerun said:
So things can be done outside of the textbook, so to speak...
Re 'crudeness' of the design - booster PFC followed by the buck down-converter is how vast majority of these things are built. Only instead of an isolated full-bridge (which is a derivation of buck topology), we use non-isolated simple buck, cutting the costs in half.
Valery.
Problem is on ALL current production EV's, they use a fully galvanically isolated design, along with a fully isolated HV system. This is done for safety and also to ensure the charger doesn't radiate unacceptable EMI/RFI into the environment which can have numerous (all bad) consequences. You can't "outside the textbook" this, it's done for a good reason. Encouraging people to be dangerous with HV DC is irresponsible and unprofessional. In addition, using a non-isolated charging system, you are going to set fault codes once the EV's on-board HV leakage detection system trips, which will immobilize the EV. (LEAF included!) The only way around this is to attempt to not ground the EV's body while charging which will create a dangerous situation and radiate tons of EMI/RFI into the environment.
-Phil
> Encouraging people to be dangerous with HV DC is irresponsible and unprofessional
;-) So much passion...
First of all, the danger is hugely overblown. If the system does not have any electrically live components accessible to the user (which it doesn't in any of these cars), there is no possibility for a shock. Isolated or not. Furthermore, if protected by a proper GFI, non-isolated is nearly as safe as an isolated design - even if there are live components accessible (again, not in these cars). If that wasn't the case, we would still all have inductive charging...
Secondly, if everyone thought like this, we wouldn't have automotive performance aftermarket industry at all. For example, increasing pressure by 2x in one's turbo engine has risks. Same for putting in a NOX system in your car. Some engines blow up. Yet hundreds of thousands of people do that. It's all about trade-offs. Learn about the potential risks, weigh them against the benefits, and make an informed decision. Not based on hearsay, ideally...
EMI/RFI - I have a couple of problems with the related statements in your post:
1. To uninitiated (i.e. not EE types), saying 'radiation' and 'bad consequences' without explaining is fear mongering. We have a pretty paranoid society here as it is.
2. 'A ton of RFI' is not a very scientific term. Have you measured it? Have you compared it with the background levels? Across the spectrum? We have measured radiated EMI from our non-grounded units - in a 0-10kHz band, at full 12kW power, at 3 feet, we measure less than 2 milli-gauss. Background level in my last 3 houses was 1.5-3 milli-gauss depending on how many lights are on...
3. Lastly, when your car moves, it's not grounded. Yet there is up to 80kW of AC power transferred around you (in a Leaf, up to 400kW in a Tesla S). And you are sitting IN the car (as opposed to you being in your HOUSE when you car charges). At freeway speeds, that AC also has much higher frequency than line - and radiated power is roughly proportional to the square of the frequency.
So let's try to not generalize things into non-quantitative categorical statements. Especially if you decide to launch a direct assault on other people like you did.
Thanks,
Valery.
