Micro-ISO Relays

An Omron Micro-ISO relay, as available through Honda

The same Micro-ISO relay next to a common Bosch relay

Basics

My search for Micro-ISO relays began with some instructions for converting an ST1300 to an electric windshield. It has a picture of the two types of Micro-ISO relays, as well as the rubber "suspension" sleeves intended to isolate the relays from vibration.

There are two common types of relays, SPST (Single Pole, Single Throw) and SPDT (Single Pole, Double Throw). SPST relays can only close a circuit. SPDT relay close one circuit at rest, and a second circuit when active. Effectively, the only difference is an extra output leg on the SPDT relays, so unless you're worried about confusing yourself, you may as well use SPDT relays and ignore the extra output leg when it's unneeded.

Sourcing from Honda

Ron Ayers shows the two-way Micro-ISO relays on their ST1300 cowl microfiche. It's item five, part number 38502-MCS-G00, "RELAY (MICRO ISO 5P)".

For reference, his same relay is available from Cycle-Parts for $6.46. Ron Ayers, by comparison, is $6.15.

A second, four-point relay is available on the ST1300 wire harness microfiche as item eight. Part number 38501-MCS-G00, "RELAY (MICRO ISO 4P)". This is a four point relay, meaning that it can only close a single circuit, rather than switching between two circuits. Since it's the same price, at $6.15, I can't see any reason not to buy the five-point relay!

Manufacturer

These relays are made by Omron. The five-point relay is Omron part number G8HN-1C4T-RH. The final H indicates "high capacity". The 4T- indicates sealed (unsealed is -2T). -1A indicates SPST ("four-point"), while -1C indicates SPDT ("five-point"). As near as I can tell, the -R indicates a suppression resistor is used (where??).

Omron's GH8N-J Data Sheet has the following specification charts. The relevant information is in bold:

Part Number		Contact Type
Unsealed	Sealed
G8HN-1A2T-RJ/DJ (DC12V/DC24V)	G8HN-1A4T-RJ/DJ (DC12V/DC24V)	SPST Standard
G8HN-1C2T-RJ/DJ (DC12V/DC24V)	G8HN-1C4T-RJ/DJ (DC12V/DC24V)	SPDT Standard
G8HN-1A2T-RH/DH (DC12V)	G8HN-1A4T-RH/DH (DC12V)	SPST High capacity
G8HN-1C2T-RH/DH (DC12V)	G8HN-1C4T-RH/DH (DC12V)	SPDT High capacity

Arrangement			SPST,SPDT
Contact material			Silver tin oxide (cadmium free)
Contact voltage drop	Standard		Less than 200 mV at 20A
	High capacity		Less than 200 mV at 35A
Max. Switching Current	Standard	12VDC	N.O. side: Inrush 100A, Steady 20A N.C. side: Inrush 50A, Steady 10A
		24VDC	N.O. side: Inrush 30A, Steady 10A N.C. side: Inrush 15A, Steady 5A
	High capacity	12VDC	N.O. side : Inrush 120A, Steady 35A N.C. side : Inrush 40A, Steady 20A

Incidentally, the G8HR line seems to be a high-capacity standard ISO relay, handling 70 amps. It uses a pinout like a typical Bosch-type relay, except that the input leg is massive.

Alternative Sources

The Mouser catalog, page 1300 lists the G8HN-1C2T-R-DC12 relay for $4.38. However, these are neither sealed (2T-) nor high-capacity (no final H), so don't use these.

Alternative Manufacturers

Tyco Electronics also produces Micro ISO relays. Their product data sheet is available here. They list two useful part numbers:

Relay Part No	Tyco order No	Contact arrangement	Contact material	Enclosure	Terminals
VFMA-21F41-S01	0-1432503-1	1 Form A (SPST)	AgSnO2	Dust cover, Sealed	Quick connect
VFMA-25F41-S01	0-1432506-1	1 Form C (SPDT)	AgSnO2	Dust cover, Sealed	Quick connect

It appears that "Form A" means SPST (can only switch on or off), while "Form C" means SPDT (can switch between two contacts). According to this page the S01 indicates a resistor (680Ω) in parallel with the coil, which presumably is analogous the -R in the Omron part numbers.