Emergency battery for radio?

[prv]

http://www.ebay.co.uk/itm/VK16D-ubl...sGames_RadioControlled_JN&hash=item3ce9c1d767

What sort of output does that produce? And I'm guessing it's either 5v or 3.3v?

NB, I still disapprove of indoor GPS antennas, but something like this could be mounted outside quite easily.

...for values of "quite easily" that include building the whole enclosure yourself

The BR355 is waterproof, so you could sikaflex it to the deck as-is with the wire going through a gland - if you wanted to. Although I have mine cable-tied to the top of a bulkhead just below the side-deck and it works fine. My AIS display, which it also feeds as well as the radio, has a GPS signal strength display mode and that invariably shows lots of nice big bars near the top of the chart, so I'm not worried about signal degradation at all. My elderly Garmin 128 did occasionally lose fix with an aerial in a similar position (since moved), showing that your disapproval was once grounded in fact, but twenty years of GPS receiver development have happened since then.

Pete

 

[SimbaDog]

Ta Food for thought!

 

[David2452]

I was on a charter holiday in Greece in 2013. That boat was equipped with a small separate battery (perhaps 30/40Ah) for the VHF and a bit of electrickery (a VSR?) that charged it from the main electrics. I was told this was required by a Greek regulation so it's not a brand new idea but seems to make sense. The battery was mounted high up in the cabin (beside the VHF set).

I didn't think much about it then and didn't study it closely. Someone round here will know more detail I expect.

Derek

It may have been installed to NMEA0400 standard, that's exactly what it specifies, not just for the VHF but for the GPS too.

 

[Carduelis]

Thanks for validating the idea and for all the useful suggestions guys. It seems odd that nobody but the Greeks seems to be doing this as a matter of course.

I'm happy to be corrected, but I imagine that immersing the main batteries, or anywhere up the cable to the radio panel, in salt water would cause them to short out immediately, and waterproofing all the connections and switches doesn't sound practical.

I still want to use the main boat set rather than relying on my handheld. 25watts at the masthead is going to give a much bigger range than any handheld at sea level even with an extension aerial. I'm now thinking that my main GPS (which feeds the DSC) should be powered this way too. It only takes between 450ma and 2 Amps peak. And in the situation where the boat is flooding I'm not going to want to talk for long. A DSC distress followed by a few minutes on Ch 16 will do me fine. The radio draws 5A on peak transmit. I'll be quite happy to revert to the handheld to talk to potential rescuers when they get near.

So, If I buy a 35 AH motorbike battery as suggested above, it's really a matter of keeping it topped up from the main domestic battery. This is 160 Ah. So what I need is a means of charging this (12v to 12v) sufficiently quickly to keep up with (say) an average 3A drain from normal usage of the GPS and radio.

 

[prv]

I'm happy to be corrected, but I imagine that immersing the main batteries, or anywhere up the cable to the radio panel, in salt water would cause them to short out immediately

While the batteries certainly won't be happy, I'm not sure about the abrupt switch-off you seem to be imagining. A day or two into my Day Skipper course many years ago, we actually had a substantial flood, up to bunk level (log impeller incorrectly fitted and popped out, and with the hatch closed to keep spray out we didn't notice immediately). I'm not sure where the batteries lived on that boat (ISTR it was a Fulmar, someone must know where they're normally kept) but we were still able to start the engine (Bukh with both starter and alternator mounted high up) once we'd bailed out most of the water. The wind/speed/depth instruments had a brain box under the chart table which died, as did the GPS, so we were without those for the rest of the week - but we still had lights and so on. I don't remember about the radio - I'm not sure we ever used it anyway as we didn't visit any marinas.

Pete

 

[pvb]

I don't remember about the radio - I'm not sure we ever used it anyway as we didn't visit any marinas.

Not maintaining a listening watch on 16?

 

[prv]

Not maintaining a listening watch on 16?

I assume we would have been as long as the radio was working. Which may have been only the first day or it may have been all week - I don't remember. We weren't in the Solent so it would have been quieter anyway

Pete

 

[lw395]

.....

I'm happy to be corrected, but I imagine that immersing the main batteries, or anywhere up the cable to the radio panel, in salt water would cause them to short out immediately, and waterproofing all the connections and switches doesn't sound practical.

.....o.

The conductivity of seawater is roughly 3 siemens/m.
It woud be hard t owork out the current exactly, but that means if ou had 12V across two metre-square plates a metre apart, the current would be 36A.
The area of exposed conductor is much lower, even if they're somewhat closer.
So I think they'd last a while, provided sea water was not flushing in and out of the cells freely.
It's a mere digression though, the battery is way more likely to be flat for othe reasons, IMHO and IME.

 

[lw395]

Thanks for validating the idea and for all the useful suggestions guys. It seems odd that nobody but the Greeks seems to be doing this as a matter of course.

...
So, If I buy a 35 AH motorbike battery as suggested above, it's really a matter of keeping it topped up from the main domestic battery. This is 160 Ah. So what I need is a means of charging this (12v to 12v) sufficiently quickly to keep up with (say) an average 3A drain from normal usage of the GPS and radio.

What I would suggest might meet your needs is a DC-DC converter which takes in 12 to 14.4V and gives out 13.8V.
The gel battery can take 13.8 indefinitely.
The converter should be powerful enough to run the radio and GPS except on Tx, which is low duty cycle in normal use.
This circuit is harder than normal because the input range has to cover both above and below the output voltage.
You may find the cheapest way to achieve this is a DC-DC intended to power a laptop, giving out say 16V, then a linear regulator down to 13.8 or whatever the battery manufacturer recommends as float voltage.

I would suggest this battery may be mounted relatively high up in the boat, so I would avoid any 'wet' batteries and go for a sealed job. When the boat is on its ear, the battey may be dripping acid on your head otherwise...
A Yuasa alarm battery might be the place to look rather than things intended to start motorbikes?

HTH?

 

[lw395]

....



...for values of "quite easily" that include building the whole enclosure yourself

...
Pete

For values of <comic title> = <PRACTICAL boat odour> AND <comic title> # < cheque book sailor >

No idea about voltages, it's random tat from ebay.
I have some ublox modules which are 3.3V, but the output can be pulled up to anything when you invert it with a transistor, which you need to do to put it into a serial port IIRC.

 

[prv]

It's a mere digression though, the battery is way more likely to be flat for othe reasons, IMHO and IME.

Certainly agree with that. Flat, or faulty, or disconnected in response to some kind of fault elsewhere in the system.

On Ariam I have a combined master switch which turns the engine and service batteries on and off together (while not at any point joining the two circuits). A faulty wiring connection caused the starter motor to begin spinning furiously, fortunately without the solenoid engaging it with the (already running) flywheel. Having stopped the engine the starter was still racing round; confused and worried that it was going to burn out I turned off the master switch. Right thing to do at that point, but it's disconcerting under way at night to lose every single piece of electrics from the cabin lights to the compass light to the depth sounder. Plenty of torches stowed around the cabin helped with the light, but a critical subset of instruments with backup power at that moment would have been a welcome bonus.

In practice I handed the helmsman my iPhone running Navionics

Pete

 

[prv]

I have some ublox modules which are 3.3V, but the output can be pulled up to anything when you invert it with a transistor, which you need to do to put it into a serial port IIRC.

So it does output NMEA, then? That's the main question I was interested in as the eBay listing gave no indication. I thought it might have been I2C or some proprietary format.

Pete

 

[lw395]

So it does output NMEA, then? That's the main question I was interested in as the eBay listing gave no indication. I thought it might have been I2C or some proprietary format.

Pete

The ublox modules I have output nmea sentences with CMOS logic levels.
As an aside, their web site had a nice little download which takes the NMEA and plots it on google earth for you....

http://www.u-blox.com/en/gps-modules/pvt-modules.html
http://www.u-blox.com/en/evaluation-software/u-center.html

 

[lpdsn]

I looked at the same idea in the spring. It's not actually that expensive to get a motor bike battery. I'd decided on a Yuasa NP 4-12, which with delivery was circa £20.

The plan was to fit a bridge rectifier to charge it off both starter & domestic batteries and not to have it's own charger. A typical Vf is 0.7V for silicon, but I was planning to use one with a Vf of 0.5V, which means that when the other batteries were charging at 14.8V, there would be still 14.3V at the VHF battery. Somewhere there is an old envelope with the type of rectifier - if I find it I'll post.

If at any stage the VHF battery falls more than 0.5V below the others, the current would come from those batteries. I included an emergency bypass switch to get the maximum voltage from a failing battery bank.

I costed up the whole project - including fusebox, LED voltmeter and various bypass switches at about £30.

The reason I didn't go ahead, apart from other more pressing jobs, was the consideration of how to secure the battery well enough, high enough up. The battery I mention is 1.75Kg. There was a suitable space above the chart table, but it would require a bit of woodwork.

You could put the GPS on the same battery.

Since then I've also considered using a lightweight 14.8V Lithium battery. I mean if they're good enough for Boeing, er...

 

[lpdsn]

Somewhere there is an old envelope with the type of rectifier - if I find it I'll post.

MBR2045CT

 

[Strathglass]

I already have built one into my boat. There is a 7Ah sealed battery located just under the deck and a switch which will transfer power to both the DSC vhf and the GPS from the domestic batteries to the emergency battery if and when required.
There is also a hh vhf which is kept on a trickle maintainence charge.
I use diode splitters to both domestic batteries and a separate diode to the emergency battery, all from the alternator. Thus full charge is maintained on all batteries.

 

[PilotWolf]

A certain local government vessel I used to work on had this very set up.

An alarm style battery as mentioned above was used to supply a (separate) radio. The battery charged from the normal charging system(I think or maybe have been a trickle charger), and the radio was normally powered from the regular ship supply. I can't remember the exact setup but it was supplied through a relay that disconnected the ship supply if it failed and brought the battery online. This was to stop the emergency battery losing power back into the ship system.

It's been a while since I read the rules but I seem to think it was required for the coding.

W.