Electronics/Emergency Power Supply

[Dockhead]

One design brief point for my hypothetical new boat which I'm struggling with is power supply for radios.

GMDSS requires an independent backup power supply for radios. Seems like following this standard would be sensible for a boat designed to be used far from civilization and rescue services.

However, unnecessary complexity and weight is also not desirable. I've never had a blackout in decades of cruising, but that doesn't prove that it's not a risk (unlike those who reason -- I've had non-ABYC gas installation for years and never blown up my boat; ergo gas is perfectly safe and there's no need to follow ABYC). I presume that the new boat will have LiFePo batts, and I guess there will be a greater risk of a blackout, since I'll be using less developed technology.

So if I do it, how to configure it? Seems to me:

1. Should be lead acid, since FLA batts like to be kept at 100% state of charge, whereas Lithium Ion batts do not. Also easier to manage.

2. Batteries, chargers, and all electronic parts of this system should be mounted in a position which will make the system resistant to flooding in case of a flooding emergency.

3. Perhaps should be echo charged from the main engine start bank. This violates the total purity and independence of this bank, with its separate alternator, no consumers, etc., but I think this is a good enough cause for that.

4. But when using the SSB for data, I will need lots of power. Can I echo charge from the main bank also? Or maybe have the engine start bank echo charger just as a backup, manually switched? Or is this getting too complicated?

5. In any case, the emergency radio bank should have an AC powered charger, powered by the regular AC system. So power can go into this bank from any part of the boat's electrical systems.

6. Now what to power with it? Just the radios as per GMDSS? Or also the navigation electronics? And maybe nav lights and emergency lighting? Bilge pumps? Does this start to get too complicated?


Besides complexity I worry about weight, but maybe a couple of extra lead acid batteries and some wiring is not such a problem on a 20 ton boat, compared to the extra margin of safety provided.

[TJ D]

Hi,

I think that a single Group 27/31 lead acid battery mounted up out of the bilge is plenty.

If your biggest draw is going to be SSB, I would suggest ditching the SSB, or at least supplementing it with a Fleet Broadband. We have one of these, and since it's been installed, I can honestly say that I have not turned on the SSB a single time. If you're contemplating a new build, this system will represent a miniscule portion of the budget. It uses far less power, and is not subject to the vagaries of propagation. You might like an iridium pilot if you're going polar. Same idea, but different satellite orbits.

I would say that the commonly available emergency nav lights that run on regular batteries would be fine. Cross that one off.

Also, an Edson emergency diaphragm bilge pump is a far more sound emergency dewatering system. Scratched...

So, my hypothetical boat is basically left with Inmarsat, VHF, and perhaps brief voice SSB off of this battery. I would say that echo charging off any source would be fine. Or wire it into your solar array. It won't take anything at all to keep it topped up anyway.

As far as I know, GMDSS only applies to vessels over 300GRT on international voyages. I'm curious about the choice of these guidelines?

TJ

[Paul L]

If you have a genst then I assume you have a genset start Fla, a main engine start Fla and the house bank Li batts. It seems like any of the Fla batts could act as a backup for your radios. Of course you,'ll have a VHF handheld that is also a partial backup.
I would suspect that a Li batt install is more susceptible to failure due to lightening given all the BMS electronics they tend to use.

[tanglewood]

A few thought...

- I would not share the battery with any start battery. The voltage drop when cranking, and the potential alternator noise when running will wreak havoc with the attached electronics. You want as clean a power source as you can manage.

- There are lots of ways to charge from other DC sources and from AC sources. Which ever you pick, I'd suggest using a three-stage charger, not an echo charger, and not a VSR. As you point out, the battery will almost always be fully charged, so you should have a charger that will quickly figure that out and switch to float voltage. An echo charger or VSR will track the voltage of the main battery bank under charge and will likely result is sustained high voltage to the coms battery causing overcharge and shortening it's life. Although I'm not a fan of Mastervolt, they do have a range of DC to DC three stage chargers that work well.

- Be sure to test your 12 coms battery at least once a year. I know people who have had a completely exhausted battery, but it was masked by the charger.

- Is your main DC power 12V or 24V? If you main power is 24V, then your 12V coms battery will power any and all 12V devices that you might have. My boat is set up this way. Radios are the primary devices, but you will likely have other nav gear than can only run on 12V and not 24V. One side effect is that you will have more devices depending on your 12V power source. I ran a failure analysis on our boat and found that one of our biggest exposures was a failure of the 12V system. I carry a spare charger, and at some point may just install it to create a redundant system.

[smac999]

I would not draw power though the emg battery being charged by the house. those echo chargers are small current. not enough to keep a battery charging with the whole nav system on especially if using ssb.

I would have back up battery on a 1-2-all switch. so normally you'd be using everything off the house bank. that way you only need a tiny charge to keep the emg battery full and ready to go. a single echo charger would do it. and keep the battery full on shore power or from engines.

have non emg stuff before the switch, and emg stuff after the switch. if total house failure. turn switch. you have x amount of hours to run off other battery depending on size of it. I wouldn't even worry about charging it under an emergancy. it's just ment to to last to call for help.

[Kenomac]

We have the house bank, the engine and generator banks with a bridge switch in case any one is low. Wouldn't that work for you? It's unlikely that everything will go dead at the same time. Then we also have the dinghy battery, but thats 12v and can be configued differently I suppose. Why not just use what you already have? I suspect your boat is set up similar, how many batteries and charging systems do you need?

Or why not add a small solar component to the mix, which will keep part of it topped off all the time?

[Dockhead]

Originally Posted by Kenomac

We have the house bank, the engine and generator banks with a bridge switch in case any one is low. Wouldn't that work for you? It's unlikely that everything will go dead at the same time. Then we also have the dinghy battery, but thats 12v and can be configued differently I suppose. Why not just use what you already have? I suspect your boat is set up similar, how many batteries and charging systems do you need?

Or why not add a small solar component to the mix, which will keep part of it topped off all the time?

We're not talking about my present boat -- but the next one, which I am designing in my fantasies so far.

Yes, the present boat is set up like you say, and it's worked fine like that. Maybe that's all that's needed and the next boat will also be like that.

I have engine start and gen start banks completely separated from the house bank, and I keep a set of jumpers cables to easily jump from one to the other if necessary.

[Dockhead]

Originally Posted by smac999

I would not draw power though the emg battery being charged by the house. those echo chargers are small current. not enough to keep a battery charging with the whole nav system on especially if using ssb.

I would have back up battery on a 1-2-all switch. so normally you'd be using everything off the house bank. that way you only need a tiny charge to keep the emg battery full and ready to go. a single echo charger would do it. and keep the battery full on shore power or from engines.

have non emg stuff before the switch, and emg stuff after the switch. if total house failure. turn switch. you have x amount of hours to run off other battery depending on size of it. I wouldn't even worry about charging it under an emergancy. it's just ment to to last to call for help.

Thanks -- that's an interesting approach to the architecture of the system, and probably the right one. The radios, plotters, and radar will all be natively 24v, and I will need droppers only for the N2K system, I think. So that should work.

[Dockhead]

Originally Posted by TJ D

. . . As far as I know, GMDSS only applies to vessels over 300GRT on international voyages. I'm curious about the choice of these guidelines? . . .

As an indication of what might be best practice.


An argument against following GMDSS on this is that with an EPIRB and multiple PLB's on board, the radios are no longer such a matter of life and death as they were for say the Titanic. So it might be that the idea of going for this very high level of failure-proofing is just not needed in this day and age.

[tanglewood]

Originally Posted by Dockhead

Thanks -- that's an interesting approach to the architecture of the system, and probably the right one. The radios, plotters, and radar will all be natively 24v, and I will need droppers only for the N2K system, I think. So that should work.

Have you found radios that are 24V? All I've seen are 12V only. Not sure why, and I haven't done an exhaustive survey by any means. They have just stood out on my 24V boat where nearly all nav equipment can accept 12 or 24V nominal voltage. I'd love to get rid of my 12V sub system, but so far remain stuck with it.

[Dockhead]

Originally Posted by tanglewood

Have you found radios that are 24V? All I've seen are 12V only. Not sure why, and I haven't done an exhaustive survey by any means. They have just stood out on my 24V boat where nearly all nav equipment can accept 12 or 24V nominal voltage. I'd love to get rid of my 12V sub system, but so far remain stuck with it.

All the commercial radio gear is 24v. I have my eye on the tasty new Icom GM600/GM600 radios.

The M801E SSB is also 24v. I unfortunately have the 12v M802, although not actually so unfortunate because I use a large Victron dropper which acts as a voltage stabilizer, and keeps the voltage at 13.6 no matter what. This enhances performance of the radio quite a bit.

[tanglewood]

Thanks. I've got an M802 as well @12V, plus 2 M506 VHFs which are also 12V only.

[Stu Jackson]

Originally Posted by Dockhead

Thanks -- that's an interesting approach to the architecture of the system, and probably the right one. The radios, plotters, and radar will all be natively 24v, and I will need droppers only for the N2K system, I think. So that should work.

Yes, good ideas. The basic choices are "automatic" i.e., a relay that closes when charging is present, or manual i.e., a switch. Your boat, your choice. It is simply a "management" issue regarding charging.

Similar to the proper use of a 1-2-B switch, as long as the emergency battery gets properly charged, then the concept is how large a bank you feel you need for that emergency based on the loads anticipated and their duration, assuming that the "emergency" bank would be used when BOTH the house bank AND the reserve/start bank died. That would be an unusual scenario, would it not?

Good thinkin', though.