The Phreatic Zone

Relay Modification

I decided to make a slight modification to the standard relay board to make it modular!

The relay conversion basically substitutes a 30A poor quality relay soldered to a custom board with a plug-in 60A relay.

When running on full load (diver with stages, dry suit etc. at full pitch) the motor will draw around 16-18A. If something gets stuck in the prop, even for a fraction of a second that peak current will increase to 40, 60 or 100A (who know’s?), what happens then is the clutch slips (if everything is set up correctly).

All this happens in a fraction of a second. That peak current is enough to weld the contacts closed on the poor quality 30A relay.

Trouble is, to replace it means un-soldering it from the board or replacing the whole board, hence the modification to a modular relay!

The standard relay is soldered to a PCB

UK Relay Mod

Batteries

In the UK the batteries you want is the Powersonic PS12180 (12v 18aH) which is wired in paralell to give you 24vdc, weighing in at 6Kg each, available here http://www.batterymasters.co.uk/proddetails.asp?ID=384&Department=SLA amongst other places!

PS12180

Power-Sonic Rechargeable Lead-Acid Battery, PS-12180 *12 volts (6 cells in a series) *Nominal Capacity 20 hour rate (900mA to 10.50volts) is 18.0 A.H. *Dimensions: 180 (L) x 76 (w) x 167mm (H)

PS12170

Power-Sonic 12 Volt, 18.0 Amp. Hrs. rechargeable SLA Battery PS12170 is air transport approved, and meets all current requirements set forth by the D.O.T., I.A.T.A., F.A.A., and C.A.B. U.L. recognises model PS-12170 under file number MH 14328 PRICED PER BATTERY Dimensions: L181mm x W76mm x H167mm (height over terminal 167mm) Weight 6.00

I have been reliably informed that the PS12170 is the same battery only without the flame retardent casing required for mod/industry applications, although the only datasheet I can find states that it is a 17aH battery!!

The price difference is negligable to be honest!

Burn-Tester

You need a 2 x 300W, 3Ohm resistors wired in paralell to give you a resitance of 1.5Ohm. I found the part numbers from RS Components http://rswww.com/cgi-bin/bv/rswww/home.do?cacheID=ukie

These are the resistors you want:-

OHMITE C300K3R1 3.1ohm 300W 040g

RS Stock no: 2508382142 Manufacturer: Ohmite Part no: C300K3R1 £16.19 each