Electronics - controlling a lopolight with an H-bridge relay

Ric

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Hello,

My boat currently has a masthead anchor light (ie only two wires up the mast) and conventional deck-level navigation lights.

I am interested in fitting a Lopolight combined tricolour/anchor light at the masthead, with the intention of using the deck-level lights when inshore, and the tricolour when offshore. However, I have no intention of trying to thread additional wires down my mast - I want to control the lights with the existing two wires.

Lopolight do offer a combined tricolour/anchor light which is controlled by two wires - however it requires installing a special and very expensive switch to swap the polarity of the two wires to select off/anchor/tricolour. This involves a lot of extra expense, and faffing about with the switchboard wires etc.

So my idea is to install a relay circuit at the masthead to reverse the polarity, controlled by my existing anchor light switch. At each alternate switch on of the anchor light switch, the masthead circuit would switch the polarity. There is apparently plenty of room inside the Lopolight mounting to fit and waterproof a relay.

Does any electronics expert know of an off-the shelf relay that could do this job?
 

VicS

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however it requires installing a special and very expensive switch to swap the polarity of the two wires to select off/anchor/tricolour.
Cant you do it with a double pole, double throw switch with centre off.
 

prv

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If the light fitting will already light one light with one polarity, and the other with the other, why put the converting relay/circuit at the top of the mast? Why not fit it inside the wiring panel or some other convenient place inside the boat?

I presume the reason for the converting circuit is that you already have a neat-looking panel that you don't want to change at all? Cos if you can fit a new switch, surely any double pole - double throw switch will reverse the polarity like this, and there are thousands of different styles available at RS et al.

Pete
 

elton

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Does any electronics expert know of an off-the shelf relay that could do this job?

You don't need a relay. You just need a couple of cheap diodes, a double pole double throw switch and a single pole switch.

l1 is your tricolour.
l2 is your masthead light
s2 swiches between the two lights
s1 turns them both off
d1 and d2 are diodes

It'll cost less than a fiver.
 

VicS

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You don't need a relay. You just need a couple of cheap diodes, a double pole double throw switch and a single pole switch.

l1 is your tricolour.
l2 is your masthead light
s2 swiches between the two lights
s1 turns them both off
d1 and d2 are diodes

It'll cost less than a fiver.

I think the point is the combined Lopolight is already designed to swtich between one light and the other by reversing the polarity of the supply. No additional diodes are necessary!

The DPDT switch is the key component!
 

elton

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I think the point is the combined Lopolight is already designed to swtich between one light and the other by reversing the polarity of the supply. No additional diodes are necessary!

The DPDT switch is the key component!
Having now looked at the technical specs for various Lopolights I'm not absolutely certain a DPDT switch is all that's needed. I'd forget the Lopolight and just fit a conventional tricolor in addition to the existing masthead light, along with the diodes and switches.
 

noelex

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Alternatively. If an aluminium mast:

Connect -ve (ground) to the mast at each end and use 1 core of the cable for one light +ve, and the other core for the other light +ve.

You can have one, the other, or both on with simple switching.

Lateral thinking :)

No please do not do this. You can get some very bad corrosion when you don’t use an earth return wire.
 

halcyon

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You don't need a relay. You just need a couple of cheap diodes, a double pole double throw switch and a single pole switch.


d1 and d2 are diodes

If you fit diodes in line with the bulbs you are droping 0.5 - 0.7 volt.

You need a centre off DPDT switch, cross wired as said.

Fit the diodes to the coils of 2 sub-miniture power relays, so one operates in polarity, the other in reverse.

The relay then switches tri-colour one polarirty supply, anchor light the other polarity.


Brian
 

nimbusgb

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centre off switch wont work for the lopolight in as far as the lopo has 3 wires coming out of it. A common negative and 2 positives ( one for Anchor / steaming and the other for tricolour ). The OP wants just two wires up the mast.

Putting a couple of diodes up at the lopolight ( building a discrete H bridge ) is the ONLY way to go. So what if there's a .7 to 1 volt drop? The Lopolight is rated from 10 to 30 volts, providing his battery does not drop below about 11 volts he's fine.

I dont have drawing tools here at work. I'll sketch it out this evening.
 

VicS

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My understanding, having now had a quick peak at Lopolight's website, is that the Tri/white is pre-wired ( with diodes?) so that it can be operated by reversing the polarity on the supply cable.

The volts drop across the diodes is of no concern as they will operate at full brightness from 10 volts to 32 volts anyway.

The details of the switch indicate that it is a DPDT switch water proof to IP56.
They say it can be replaced with another DPDT switch.
 

pvb

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My understanding, having now had a quick peak at Lopolight's website, is that the Tri/white is pre-wired ( with diodes?) so that it can be operated by reversing the polarity on the supply cable.

I don't think that's right at all. The Lopolight Tri/Anchor has 3 wires - a common negative, and a positive for each of the 2 functions. Reversing polarity isn't a solution. A simple diode arrangement in conjunction with a changeover switch will work. This is effectively the system which Lopolight sell as the 400-012 switch, which appears to be around £100!
 

VicS

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I don't think that's right at all. The Lopolight Tri/Anchor has 3 wires - a common negative, and a positive for each of the 2 functions. Reversing polarity isn't a solution. A simple diode arrangement in conjunction with a changeover switch will work. This is effectively the system which Lopolight sell as the 400-012 switch, which appears to be around £100!

You are right.

Would this do the trick?

scan0067.jpg
 

VicS

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Yes I can see that now. I dont know why I thought your circuit would not work?

Yes I can, Ithink.

to get yours to work you would have to reverse the connections to one of the individual lights. Unless they are not polarity sensitive. May be thats easy to do.

What I am suggesting can simply pick up the three connections without alteration. Common negative and the two positives
 
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