What main contactor to use for AC system with regen?
 

I have searched around and i am finding it difficult to select a main contactor.

The main concern i have is that most contactors seem to have polarity preffernces. The main contacts being labelled with + and - or A1 and A2. Because the current can flow in either direction in an AC setup with regen i don't want to damage the main contactor.

Several data sheets for contactors mention things like magnetic blowouts which i have heard don't like reversed current flow.

Anybody with an AC motor setup like to share their contactor experiences?

Vacuum contactors work fine for both AC and DC. They do not use magnetic blowouts. They are a bit more expensive than a DC contactor. And of course you'd need 3 phases instead of 2.

I use a DC contactor from the battery pack to the controller. If you shut off the power to the controller, the motor (AC or DC) will coast (or the AC can regen, depending on how your controller is set up).

An AC contactor (perhaps with an overload block) would go between the controller and motor. Are you using the contactor for reversing?

The main contactor should be on the battery pack and there for should be a DC contactor, non that I have seen care about positive or negative and work fine for regen.

I use an Albright Contactor.

http://www.albrightinternational.com...ct%20Range.pdf

I had a look at the Albright site. They talk about polarity sensitivity and magnetic blowouts.

Blowouts enable the contacts to switch D.C. voltages of 48v or higher. Fitting of blowouts usually makes the contacts polarity
sensitive and where this is the case the positive markings ‘+’ on the top cover of the contactor must be observed. Magnetic Blowouts
can be used with certain ‘P’ type switches, but we do not advise them suitable for frequent current switching applications. The suffix
’B’ denotes the fitting of magnetic blowouts.
Note:
The SW200 series is fitted with magnetic blowouts as standard therefore the option is to not have blowouts, this is indicated by
the suffix ‘N’. Also relevant to the SW200 range is the suffix ‘R’ which denotes non polarity sensitive blowouts are fitted.

So if i read that correctly they put in the magnetic blowouts to help deal with voltages over 48v. This normally makes the contact polarity sensitive unless non polarity sensitive magnetic blowouts are used.

I am not using the contactor for reversing, it is just for isolating the battery pack from the controller, DC-DC converter etc.
This contactor will see current from the battery pack to the controller and when in regen will see current from controller to battery pack. This is why i was worried about contactors that had polarity markings on the case for the main contacts.
The Vacuum contactors you mentioned, would these be like the contactors from Kilovac?
I was looking at the Kilovac contactors on eBay and in the photos they have polarity marking on the main contacts.

Contactors aren't cheap and i would hate to get the wrong type.

The power between the batteries and controller is always DC, even on an AC system. The polarity sensitive Albright will work.
Regen current will never reach normal current levels. Besides, AC systems do not typically fail in the same manner as DC (short circuited) where blowouts are necessary.

Per Mechman600's post, the battery bank is isolated from the controller by a DC contactor (I would add 'or a vacuum contactor').

The polarity is an issue when you are trying to break the flow of current, like during a short circuit of the battery or when the power electronics on the controller fails.

For a main contactor, you connect the + battery cable to the + on the contactor and it's hard wired that way, polarity doesn't change so a polarity sensitive contactor will work just fine.

I think Astro is wondering about the change of polarity when in regen, when current is flowing back to the pack, and how this affects the polarity of the contactor's blowouts.

This is a non-issue because contactor blowouts are meant to break high amounts of DC current in the event of a DC controller failure, as stated above. However, unlike a DC controller, an AC controller is highly unlikely to fail in a closed/shorted state, making a contactor with blowouts unnecessary.

I think the confusion here is thinking polarity changes while regen.
The polarity (ie. direction of flow) does not reverse during regen. It continues to flow around the circuit in the same direction. Only the motor is now pushing - to the battery instead of pulling from the battery + .

Hope this clears things up.