Autopilot control, Solid state relays

[roland stockham]

Hi all
I am fitting a new below deck autopilot using the Octopus pump which draws about 20a max. My current computer (Raymarine XP5) has a peak out put of about 6A but works very well.

So decided to simply control the pump using a paid of external relays. Solid state seems to be the way to go. All seamed fine until I tried to actually buy the relays!

Electromechanical relays are no problems, 12v control circuit and enough amps on the output but does no care whether it is AC or DC

Looking at the spec's for SSR's there are plenty with 12v DC control imputs but most of them seam to be 30-240v AC on the switched circuit. I can't find any information about whether that means they will swtch a low votage DC load as well. Anyone now how these things work?

[goboatingnow]

Try www..crydom.com

The AC units will not switch DC , they use SSR , the DC ones uses mosfets

You need to spec these SSRs carefully, they can be fragile electronically , carry spares !

Dave


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[roland stockham]

Thanks Dave. Given that they are 4x the price of standard automotive relays do you recon they are worth it. I can get machanical relays and 2 spares for about $20 (and replacements at any auto shop). 2 SSR's plus one spare will be close to $70 and spares are order only. Which would you opt for?
Autopilot is critical as I may be sailing Panama to Hawaii SOLO this summer (do have a windvane as well)

[olaf hart]

You are going to need four relays and a couple of diodes for an H Bridge.

[Cap Erict3]

I did the very same mod. I used relays at first but after reviewing the specs on the power transistors did away with the relays.

I have since put a 1000+ miles on the autopilot without a hitch.

When testing prior to doing away with the relays I never saw more than 4 amps on the pump.

[deblen]

Google Comnav Marine CT2 motor controller.
There is a used CT3 on ebay cheap at present-not sure if it will work for ur situation,but I think it can be modified to.
Cheers / Len

[Cap Erict3]

The MOSFET's are IRFZ48NS.

Data sheet here

http://www.irf.com/product-info/data...a/irfz48ns.pdf

[goboatingnow]

Originally Posted by roland stockham

Thanks Dave. Given that they are 4x the price of standard automotive relays do you recon they are worth it. I can get machanical relays and 2 spares for about $20 (and replacements at any auto shop). 2 SSR's plus one spare will be close to $70 and spares are order only. Which would you opt for?
Autopilot is critical as I may be sailing Panama to Hawaii SOLO this summer (do have a windvane as well)

In general , good quality relays will be ok , personally I'd use solid state

Is yours a constant running pump or a reversing one. ,?

Dave


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[Frankly]

Most modern autopilot controllers use pulse width modulation to achieve variable speed control of the DC drive motors. You can have a bang/bang control of the driving motor, it is just a lot harder on the components. Might want to look at the actual motor drive signal before choosing a higher power output stage. Amplifier might give more satisfactory control vice relay.

[goboatingnow]

Originally Posted by Frankly

Most modern autopilot controllers use pulse width modulation to achieve variable speed control of the DC drive motors. You can have a bang/bang control of the driving motor, it is just a lot harder on the components. Might want to look at the actual motor drive signal before choosing a higher power output stage. Amplifier might give more satisfactory control vice relay.

You can set nearly all APs to control directional only not speed for constant running pumps etc that signal can be used.

But I agree a look at the waveform would be helpful. I don't remember the Raymarine APs bring pwm though

Dave


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[roland stockham]

Thanks Olaf I looked up H bridges and found these which seam ideal Robot Power Products - Simple-H & HV - H-bridge. Much simpler than trying to make my own and cost about the same

[Cap Erict3]

http://www.cruisersforum.com/forums/...ad.php?t=75897

Pm sent.

[CLady]

I don't know how those relays work. I have a 15 year old Autonav hydraulic drive (equivalent of the Type II drive size) hooked up to the steering quadrant with my new Raymarine EV 400 computer that I installed and really like it. In heavy conditions with lots of yawing, it drew max 20 amps and kept up with the boat's needs.

That Octopus unit looks good.

[CLady]

My question would be if they are marine grade switches.

[wgoodbye]

I've looked at the exact same project, X5 AP connected to Octopus HLA. I looked at a lot of options for relay and came up with the Crydom DP4R60D20. Its a DC Reversing Solid State Contactor
• Ratings of 20, 40 & 60 Amps
• Load voltage ratings of 1-48VDC

A little pricey but seems like the perfect fit.

You can find a spec sheet on it here:

http://www.crydom.com/en/Products/Catalog/d_p4_r.pdf