AC Contactor in Solar Inverter, Battery Charging

The first will probably have a DC coil.

really? I can't see the schematic from here

Before your inverter can be be connected to the AC line, the frequency and phase must be matched or bad things (i.e. some sort of destruction) will happen. Since you didn't include the details, it is impossible to know how the solar power feed accomplishes this match up. That is "grid compliance". The mechanical equivalent is similar to grinding gears in a standard automobile transmission (a synchronized load) but when you connect two power sources one may try to kill the other if not in sync.

A standard contactor does not worry about compliance because it is not usually used to connect two AC energy sources together. A contactor usually just opens and closes the connection of some load to a power source.

I suggest difference will be that solar contactor will have a high isolation standard - it has to automatically ensure isolation from mains. A motor contactor does not have to be an isolator, because a starter normally has a manual isolator switch.

Isolation devices have, for safety reasons, specific requirements for contact gap (when open) and breakdown voltage.

This Panasonic LF-G relay type came up on Globalspec for solar inverter contactor...........

http://www.globalspec.com/specsearch/partspecs?partId={E6B28428-E46A-44BF-B838-6D8B86762D68}&comp=317&vid=90846&sqid=19144240

Note the emphasis in brochure extract below on safety standards, contact gap, insulation, creepage path length, clearances and breakdown voltage.

Also it is DC operated - AC contactors have a fluctuating magnetic flux and finish up with a slow release because they have to hold contact pressure through the "current zeros" of the coil current. I expect a solar inverter will have a fast disconnect requirement, the LF-G has 10 ms release.

Features

• High capacity
  High capacity control possible at 22A/31A (High capacity type) 250V AC rating in compact size (L: 15.7 × W: 30.1 × H: 23.3 mm L: .618 × W: 1.185 × H: .917 inch)
• Contact gap: 1.5 mm .059 inch
  Compliant with European photovoltaic standard (VDE0126).
  EN61810-1 certified: 2.5 kV surge breakdown voltage (between contacts)
• Coil holding voltage contributes to saving energy of equipment
  The coil holding voltage can be reduced up to 35%V of the nominal coil voltage (Ambient temperature: 20°C 68°F).
  Power consumption at the lowest coil holding voltage: 170 mW equivalent
  *Coil holding voltage is the coil voltage after 100 ms from the applied nominal coil voltage.
  *When the ambient temperature during use is 85°C 185°F, make the coil holding voltage between 45% and 80%V of the nominal coil voltage.
• High insulation resistance
  Creepage distance between contact and coil terminal: Min. 9.5 mm .354 inch
  Clearance distance between contact and coil terminal: Min. 6.5 mm .256 inch
  Surge breakdown voltage: 6 kV
• Conforms to various safety standards

Typical Applications

• Photovoltaic power generation systems (Solar inverter)
• Uninterruptible Power Supplies (UPS)
• Home appliances
• Office equipment

I suggest you compare a motor starter contactor specification - they will have more emphasis on number of operations and contact overload (motor start 6 -8 times rated current).

Siemens has 3TS converter duty ,ABB has AF..T range for solar inverter,UPS & battery application.

I believe it requires simply AC1 duty . so can I select simply Eaton freedom series in AC1 category ?

No. Eaton Freedom series are motor contactors to NEMA standards.

Your post asked for the differences between contactors for solar inverters and motor contactors which I explained. I have looked at the Eaton website data and there is nothing "standing out" about isolation service for these contactors.

You did not state the phases,frequency voltage or current rating of your requirement - you have not actually stated clearly that you require a relay/contactor for connecting a solar inverter to mains.

It is not clear if you are designing a system or repairing it. There is a distinct difference of coil loading and behaviour between inverter contactors and the Eaton motor contactor - thus it will likely not work properly and could cause damage if used as a spare.

I am trying to figure out existing contactor can be used in solar ( AC side )? or there need be change in contactor ,coil design.

The normal design of AC coil for a motor contactor is for an AC supply.

Initially, the gap in the magnetic circuit is large. A large "air gap" in the coil magnetic circuit requires low inductance and maximum current and ampere-turns for strong pull to move the armature and the contacts.

When the armature has moved-in, the air gap is much smaller [a minimum gap - might be ensured by non-magnetic filler - is necessary to avoid hold-in by remanent magnetism of iron after coil is de-energised]; inductance is much higher and AC current is reduced to a "holding" value which does not overheat the coil.

Because current, flux and magnetic pull pass through zero twice per cycle; the contacts would experience a fluctuating pressure and be subjected to excessive cyclic mechanical stress without "over-sizing".

To minimise this, to a proven level for 20+ years life, the standard solution is to have a solid copper ring around part of the iron - the current in this, thinking of it as a resistive-loaded secondary turn on a transformer (primary is the main winding), is in phase with the coil voltage while the main current lags voltage nearly 90 degrees as an inductive circuit. This "shading coil" flux provides a pull on the contacts when the main winding current is zero.

It should be realised that this design causes a lot of noise and vibration at 100/120 Hz and some modern motor contactors have gone to a quieter DC design with integral bridge rectifier which can be installed closer to personnel without problems.

It is relatively easy to supply this basic AC design with DC to energise the coil - the problem of continuous current overheating the coil requires a ballast resistor switched-in by a late break contact. But it is not efficient for low closing current or holding power.

I think that solar inverters would require the mains connection contactor coil to be powered from the DC panel side - it makes sure there can be no connection when it is dark.

Eaton do not give DC coil data in basic brochure - you would have to e-mail them for details. As I wrote previously, there is no indication Eaton meet electrical isolation requirements.

Since you give no voltage, phases and power your contactor must switch, no one can suggest any make or model.

Still did not get answer ..looking what exactly manufacturer doing to make contactor fit for solar and battery charger application.( no immediate application I am having..)

See below contactor ..

http://www.siemens.co.in/pool/about_us/our_business_segments/industry-automation/cp/3ts-converter-duty-contactors---brochure.pdf

What I found to note in the 3TS brochure was....

1. Emphasis on AC1 duty - electronic equipment usually has its own, fast acting, current limits backed by quick acting semiconductor type fuses and is required to have high power factor to minimise current load - so high inrush currents of other duty types are absent. Synchronisation for connection of inverters to mains is with very accurate frequency, phase and voltage matching, so little stress.
2. Low contact voltage drop for system efficiency and small size. Also reliability at small voltages - necessary considering low voltage at close implied by 2nd sentence of 1.
3. Testing to prove the high cycle rate on no load - since no-load connect/disconnect is feature of inverter duty, see 1., it is necessary to ensure reliable connection - compare many other duties where current at make/break is normal load or more.
4. Low holding power, particularly on DC for system efficiency and because low loss in the contactor favours small size and cost for applications by the million.