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Confused over relays


Dr Bob

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1 hour ago, Tracy D'arth said:

Very poor practice to duplicate relay contacts to double current carrying capacity,  It is not a sensible idea as there is always a contact that makes or breaks fractionally before the other.

When I worked on Admiralty and Army equipment it was a total no-no.

 

Those rocker switches are weedy, I've had loads fail, hence the power wasting relays.  Who in his right mind designed all this gear?

 

I would dump all the rocker switches and the relays and use the Hagar MCBs as switches, I not sure though that the Hagar product is intended for DC use. I do know that Merlin Gerin, now Schneider, are approved, we used them in telephone centres.

 

I too am dismayed by this design, presumably done by a non-boating electrician. As you say use the MCBs rather than the switches and relays, the back to basics approach would be better, though will not present an attractive looking panel to the user.

 

Regarding the comment on duplicated contacts, such an approach  is also not testable without disconnection of wiring. Very much a no-no in the nuclear industry for this reason.

 

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Aqualine are famous for these relays! Seems a clumsy and complicated way of doing it! We have computer and CANBUS  controlled MOSFET switching for our DC loads which may be complicated, but isn’t clumsy!

 

On the question of the relay current, note it is only 140mA or so so it’s not going to make a big difference to current displayed on BMV. And modern LEDs probably only use a couple of mA.

 

On the practice of paralleling the contacts I don’t see a problem provided the max current can be handled by one of the contacts. Paralleling them just reduces contact heating. The contacts are rated at 25A each and I can’t think of a boat circuit that would use more than that.

Edited by nicknorman
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Might not be a good idea to bypass the relays. They are a switching device to take the load where the panel switch isn't built to take higher currents. Small current activates the relay, which can then handle the heavier currents. 

 

 

Edited by Higgs
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1 hour ago, Onewheeler said:

Why not take a relay out and measure the coil resistance.

Access is not easy. If it was, I would have measured it!

Significant faffing required - hence asking the questions before starting to dismantle.

56 minutes ago, Higgs said:

 

Might not be a good idea to bypass the relays. They are a switching device to take the load where the panel switch isn't built to take higher currents. Small current activates the relay, which can then handle the heavier currents. 

 

 

Yes, I understand that...but there is a circuit breaker in the circuit as well as the relay and very few of the circuits ever get switched ...so if the current draw is significant then worthwhile shorting out the relay and relying on the MCB.

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3 minutes ago, Dr Bob said:

Access is not easy. If it was, I would have measured it!

Significant faffing required - hence asking the questions before starting to dismantle.

You breezed past comments made about possible effects on your warranty so I take it you are, not bothered, dont care or have had confirmation from Aqualine that there will be none?

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2 hours ago, Dr Bob said:

Yes, I understand that...but there is a circuit breaker in the circuit as well as the relay and very few of the circuits ever get switched ...so if the current draw is significant then worthwhile shorting out the relay and relying on the MCB.

 

Isn't the relay passive, until the panel switch is thrown on, and therefore drawing no current.  Obviously, a more robust panel switch would handle a higher current in the first place, without the need for a relay, but the ones you have are not made to take heavy currents. 

 

  

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6 hours ago, Higgs said:

 

Isn't the relay passive, until the panel switch is thrown on, and therefore drawing no current.  Obviously, a more robust panel switch would handle a higher current in the first place, without the need for a relay, but the ones you have are not made to take heavy currents. 

 

  

The relays only draw current when ‘on’, but normally most will be on all the time as you don’t want to trot down to the switch panel to turn on the kitchen light, or to turn on the pump to fill the kettle or empty the shower, these circuits work best with local switches/automatic switches, hence have a 24/7 supply.

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2 hours ago, Chewbacka said:

The relays only draw current when ‘on’, but normally most will be on all the time as you don’t want to trot down to the switch panel to turn on the kitchen light, or to turn on the pump to fill the kettle or empty the shower, these circuits work best with local switches/automatic switches, hence have a 24/7 supply.

 

Yes, they will be drawing current when activated. Maybe the solution is to fit new panel switches, and ditch the relays.  

 

 

 

Edited by Higgs
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9 hours ago, Dr Bob said:

Access is not easy. If it was, I would have measured it!

It looks simple  from your picture to drop one neutral / live wire from a relay and measure the coil resistance without removing the relay. I have had to do similar many times at work.

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45 minutes ago, Loddon said:

It looks simple  from your picture to drop one neutral / live wire from a relay and measure the coil resistance without removing the relay. I have had to do similar many times at work.

Not necessary though, the spec sheet says 1.7 watts at 12v so the coil resistance is 85 ohms and current is 141mA. Each relay consumes 3.38 Ah in 24 hrs. So if there are 10 relays, that is not far off the consumption of a 12v fridge.

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10 hours ago, The Happy Nomad said:

You breezed past comments made about possible effects on your warranty so I take it you are, not bothered, dont care or have had confirmation from Aqualine that there will be none?

IF we do the modifications then these will be done before our 2021 cruise starting in April/ May, at which time I only have a month or so left on the warranty. So no, I am not bothered. 

 

The problem with new boats is that they are never perfect and some things have to be changed. This thread has persuaded me that I will only save around half the power initially identified in the Farcebook post so I need to weigh that up against the negatives, and given I am using Lithium's, I am far less worried about power. I will ponder the issue over the next few months.

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18 minutes ago, Dr Bob said:

IF we do the modifications then these will be done before our 2021 cruise starting in April/ May, at which time I only have a month or so left on the warranty. So no, I am not bothered. 

 

The problem with new boats is that they are never perfect and some things have to be changed. This thread has persuaded me that I will only save around half the power initially identified in the Farcebook post so I need to weigh that up against the negatives, and given I am using Lithium's, I am far less worried about power. I will ponder the issue over the next few months.

I never truly appreciated you only get a years warranty with a new boat so I have learnt something new today. Seems a bit on the tight side to me considering on vehicles costing half to a third of what you pay you get three.

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11 minutes ago, The Happy Nomad said:

I never truly appreciated you only get a years warranty with a new boat so I have learnt something new today. Seems a bit on the tight side to me considering on vehicles costing half to a third of what you pay you get three.

If you believe in that year then you may well be disappointed. Most companies "building" narrowboat are very small so what do you do when they refuse to rectify issues or make excuses as to why they can't. There are a number of examples of companies liquidating when faced with court orders.

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34 minutes ago, Dr Bob said:

This thread has persuaded me that I will only save around half the power initially identified in the Farcebook post so I need to weigh that up against the negatives ...

May I remind you that current is preserved around a circuit, thus the power saved in the negatives will be the same as the power saved in the positives and thus the overall power saved will be as identified.
 

 

Or something like that.

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5 minutes ago, David Mack said:

So what circuit breakers and panel switches would the team recommend to someone starting afresh on their boat electrics?

KISS. For panel switches, it is hard to beat big old fashioned metal toggle switches. They use a round panel hole, which is much easier to cut than a rectangular one, are designed to break DC currents, look good and can take high currents. What is not to like?

Example.

 

For circuit protection, I'd go for blade fuses in a multiway fuse box. My boat has breakers in a commercial panel, plus some fuses for things like the battery monitor. I've never had a fuse blow, or breaker trip, so starting from scratch, be happy perhaps having to replace a fuse once in a while. Blade fuses are used in vehicles, so known to work with vibration, moisture, 12V and high currents and cheap.

 

Jen

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4 minutes ago, The Happy Nomad said:

I never truly appreciated you only get a years warranty with a new boat so I have learnt something new today. Seems a bit on the tight side to me considering on vehicles costing half to a third of what you pay you get three.

I am sure the bumph says 12 months (I must check?)...but the warranty varies i.e. The engine/gearbox is 5 years, they seem to be covering the paintwork for 3 years or more, the washer dryer is 5 years(?) etc. For me it's about the sale of goods act ( or its successor) i.e. Is it fit for purpose. Aqualine / new and used are quite good. If I rewire then yes I must suffer the consequences but I need to work out what can go wrong. Not a lot in this case. Of all the circuits I could bypass where things go wrong is the water pump....as that could break any time...but I have a spare....but likely I would not do the water pump circuit as it is useful to have the switch where it is for when the tank runs empty.

I have already wired in a set of Li batteries in parallel with the supplied batteries and formally written to new and used with the modifications, operating procedures and risk assessment and have accepted that I will cover any faults on the domestic alternator.

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3 minutes ago, Tony Brooks said:

If you believe in that year then you may well be disappointed. Most companies "building" narrowboat are very small so what do you do when they refuse to rectify issues or make excuses as to why they can't. There are a number of examples of companies liquidating when faced with court orders.

I think I agree with Tony. When we bought the boat, the warranty was to me a bonus. Something to think about if something major went wrong, i.e. The engine or the paintwork but I had to be able to cover anything else. Our contract is with new and used who could go out of business but not very likely (probably one of the safest companies at the moment the way 2nd hand boat sales are going). Hopefully N&U will be around in 3-5 years time if major problems appear but buying a new boat is a risk with far far less protection than buying a new car. Minor problems I will fix myself.

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19 minutes ago, Jen-in-Wellies said:

KISS. For panel switches, it is hard to beat big old fashioned metal toggle switches. They use a round panel hole, which is much easier to cut than a rectangular one, are designed to break DC currents, look good and can take high currents. What is not to like?

Example.

 

For circuit protection, I'd go for blade fuses in a multiway fuse box. My boat has breakers in a commercial panel, plus some fuses for things like the battery monitor. I've never had a fuse blow, or breaker trip, so starting from scratch, be happy perhaps having to replace a fuse once in a while. Blade fuses are used in vehicles, so known to work with vibration, moisture, 12V and high currents and cheap.

 

Jen

Another plus point for blade fuses is when fault finding it is easy to pull a fuse then measure the current flow by either plugging in a loop and using a clamp meter, or by sticking your meter probes into the fuse holder.  Obviously don’t use this method if you suspect a downstream dead short as the current will be massive.

 

added or even something like this. 
https://www.ebay.co.uk/itm/Automotive-Current-Tester-Circuit-Meter-Standard-ATO-ATC-Blade-Fuse-Car-Vehicle/400433639239?hash=item5d3bb46f47:g:AocAAOSwS~FaXd5V

Edited by Chewbacka
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1 hour ago, David Mack said:

So what circuit breakers and panel switches would the team recommend to someone starting afresh on their boat electrics?

On the domestic side for 12v I do not have a switch panel  only a fuse board, I can see no reason for a switch panel all it does is introduce another failure point, if I need to power down a circuit I pull the fuse. All the lights and USB sockets are switched locally using standard domestic switches (yes I know they are not DC rated but in 30 years I have only had one fail and that was O/C) now that loads have decreased due to LED lighting I suspect I will not see another failure.

I have always stuck with the principle of fuses for DC and breakers for AC so you know which is which without having to read a label.

Very few MCB are DC rated the only ones I can think of are some Merlin Gerin but since the takeover by Schneider not all MG are.

Its best to check the specs..........

 

 

When I say I have a fuseboard that is exactly what I mean its an old wylex domestic one like this marked to show its use at 12vDC

 

wylex-fuse-board.jpg

Edited by Loddon
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1 minute ago, Loddon said:

On the domestic side for 12v I do not have a switch panel  only a fuse board, I can see no reason for a switch panel all it does is introduce another failure point, if I need to power down a circuit I pull the fuse. All the lights and USB sockets are switched locally using standard domestic switches (yes I know they are not DC rated but in 30 years I have only had one fail and that was O/C) now that loads have decreased due to LED lighting I suspect I will not see another failure.

I have always stuck with the principle of fuses for DC and breakers for AC so you know which is which without having to read a label.

Very few MCB are DC rated the only ones I can think of are some Merlin Gerin but since the takeover by Schneider not all MG are.

Its best to check the specs..........

 

I’m inclined to agree about the need for switches. For a few items eg water pump and maybe fridge, yes. But why the need for control panel switches for eg lighting, when that lighting is actually controlled by switches in the cabin? In 10 years we have had one ( virtual) fuse blow, due to a short in the tunnel lamp wiring. In our case fuses are reset electronically, but even if we had mechanical fuses it hardly seems onerous to have to replace one fuse in 10 years.

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Just now, nicknorman said:

I’m inclined to agree about the need for switches. For a few items eg water pump and maybe fridge, yes. But why the need for control panel switches for eg lighting, when that lighting is actually controlled by switches in the cabin? In 10 years we have had one ( virtual) fuse blow, due to a short in the tunnel lamp wiring. In our case fuses are reset electronically, but even if we had mechanical fuses it hardly seems onerous to have to replace one fuse in 10 years.

 

It looks pretty and gives the boat an air of lots of things going on. Lots of switches with lights - better than a Christmas tree. 

 

 

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5 minutes ago, nicknorman said:

I’m inclined to agree about the need for switches. For a few items eg water pump and maybe fridge, yes. But why the need for control panel switches for eg lighting, when that lighting is actually controlled by switches in the cabin?

Switches for Fridges and pumps will have to be decent size ones, I never switch either off when we are onboard and just pull the pump fuse when we are away for the winter (fridge is 230v). Having said that there is a switch next to the water pump under the bed, I have never used it as pulling the fuse is easier ;)

 

 

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29 minutes ago, Loddon said:

On the domestic side for 12v I do not have a switch panel  only a fuse board, I can see no reason for a switch panel all it does is introduce another failure point, if I need to power down a circuit I pull the fuse. All the lights and USB sockets are switched locally using standard domestic switches (yes I know they are not DC rated but in 30 years I have only had one fail and that was O/C) now that loads have decreased due to LED lighting I suspect I will not see another failure.

I have always stuck with the principle of fuses for DC and breakers for AC so you know which is which without having to read a label.

Very few MCB are DC rated the only ones I can think of are some Merlin Gerin but since the takeover by Schneider not all MG are.

Its best to check the specs..........

 

 

When I say I have a fuseboard that is exactly what I mean its an old wylex domestic one like this marked to show its use at 12vDC

 

wylex-fuse-board.jpg

Oh so true. Our Wylex board like that on Jenny B gave 30 years service with no problems and as far as I know continues to do so. The only "problem" was that when the idiot (me) working on the wiring caused a short it needed fuse wire to fix and that does not seem so easy to get hold of NOW these days. Blade fuses are far easier.

 

In the case of an urgent need to turn off a domestic circuit you still have the master switch pending pulling a fuse.

 

This modern practice of fancy control/mcb/switch panels seem to me to be all to do with eye candy rater than reliability.

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