Always on devices - house or starter battery?

[basssears]

Currently have a few "always on" devices (buzzers for high water temp, low oil pressure, high water alarm, bilge pump) currently hard wired to the start battery, going to be moving these off the batteries and onto a bus bar / fused block.

My question is, what should I be connecting my fuse block to? Keep in mind, these are things I do NOT want to have switched on any panel anywhere as I want them to be always hot (well bilge pump #1 has its own switch but it's hidden away from sticky fingers).

Seems my options are:
1) Connect to start battery... it's more likely to have full charge than house, and less likely to be accidently drained, but it's only one battery and therefore much less capacity.
2) Connect to house bank... three deep cycle(ish) batteries instead of one, so that's a plus, but they are conceivably more likely to run dead some day from an overacting fridge etc. etc.
3) I guess I could connect to the 1->2 battery switch and then my always on appliances just go from wherever the battery switch is set, but not sure I like this as it makes it possible to turn off these things I want always on.

Is there a set way of doing this? Are my three choices above not the brightest ideas?

-- Bass

[Dave-Zim]

Hey Bass.

I would connect to house bank and invest in a device to disconnect your house bank from normal loads when battery voltage drops to a set level. 12.2v or similar.
That way, you have the safety of the critical loads being connected to the largest battery bank. Also, you would have the added safety of your house bank never being totally flattened.

Low voltage disconnects aren't huge money and would give you peace of mind I think.
obviously critical loads would bypass the disconnect.

Dave

[deblen]

My opinion only.
Connect to house battery. Do not use low voltage disconnect.

My personal reasoning:
1. I always want the ability to start the engine-it could get my sinking boat to a beach,where salvage is more feasible.

2. I would rather flatten my house bat.,or even ruin it,than have the boat sink.

3. Items that I don't want turned off (B pump,fume alm,etc. are safety items.
I have to actually remove a fuse to de-power them. No chance of accidental disconnect. I won't even use a switch style breaker.

Paranoid ? Probably,but I sleep better.

Here is a basic diagram.

https://www.dropbox.com/s/l7fuzp9c45...ching.pdf?dl=0

[Dave-Zim]

Originally Posted by deblen

My opinion only.
Connect to house battery. Do not use low voltage disconnect.

My personal reasoning:
1. I always want the ability to start the engine-it could get my sinking boat to a beach,where salvage is more feasible.

2. I would rather flatten my house bat.,or even ruin it,than have the boat sink.

3. Items that I don't want turned off (B pump,fume alm,etc. are safety items.
I have to actually remove a fuse to de-power them. No chance of accidental disconnect. I won't even use a switch style breaker.

Paranoid ? Probably,but I sleep better.

Here is a basic diagram.

https://www.dropbox.com/s/l7fuzp9c45...ching.pdf?dl=0

Low voltage disconnect is there to ensure non critical loads....like fridges and lights, are disconnected BEFORE battery is flat. This ensures there is enough energy kept in the batteries so that critical loads are guaranteed a reasonable amount of power so they can continue to work. Critical loads will still be able to run to the bitter end. The LVD just ensures they have the best chance of doing so.

[sailorboy1]

I connect my "always on" loads to the house battery. My thinking is that if they drain the house battery I still want to be able to start the engine, and that if the house battery were to be drained by the load that the small start battery is a drop in the bucket.

[pcmm]

Bilge pump and VHF should be wired to the house battery ALWAYS! the house bank almost always has far greater capacity than the start battery. the rest can stay on the start battery as they're only relevent when the engine is running and therefore charging the start and house batteries

[blackswan555]

buzzers for high water temp, low oil pressure,

Usually on ignition switched feed ?

Tim

[jeepbluetj]

It may very likely depend on the usage of your boat. Mine is a weekender. My #1 priority is the bilge pump. So I've got the bilge pump wired to both the main and the backup batteries with a couple of diodes. It'll run off of whatever battery has the most voltage in it.

Yes, that does mean I can flatten both batteries with the bilge pump. That's OK by me because if I'm on the boat I'd notice it way before that. If I'm off the boat I want the pump running if it needs to.

My CO detector runs on AA's.

Those are the only 2 things that are always on.

[deblen]

Originally Posted by Dave-Zim

Low voltage disconnect is there to ensure non critical loads....like fridges and lights, are disconnected BEFORE battery is flat. This ensures there is enough energy kept in the batteries so that critical loads are guaranteed a reasonable amount of power so they can continue to work. Critical loads will still be able to run to the bitter end. The LVD just ensures they have the best chance of doing so.

Ahh Good plan!

[Dsanduril]

If you really want the belt-and-suspenders approach, connect them to both battery systems. The cheap way is a couple of diodes of the appropriate size in the line, seeking those that have the lowest voltage drop.

The expensive way is get yourself a MOSFET-based power supply redundancy module (and the intermediate way is a pre-manufactured diode-based redundancy module). Redundancy modules are standard equipment in many industries, finding one that you would be satisfied with in the marine environment would be the time-consuming part.

[basssears]

Thanks everyone, this definitely helped clear up my thinking. Lots of good ideas here... what has solidified for me is:

1) Connect my critical "always on" devices to fused bus bar connected directly to house bank.
2) Put low voltage disconnect between house bank and panel (so non essentials can't kill batteries, but essentials could still use all of battery if they needed to (your point is well taken Deblen). Probably use Blue Sea m-LVD, seems solid. Thanks for this Dave, wasn't familiar with these.

Crude schematic attached...

Off to Defender's sale I guess

[deblen]

Link to Lo Volt disconnect Blue Sea m-LVD Low Voltage Disconnect

[smac999]

your engine things (oil pressure, temp etc, should be on the engine battery. and have no reason to be unswitched. infact they should probably be ignition controlled.




the bilge pump and high water should be on house unswitchd.

[Swift Drift]

Originally Posted by smac999

your engine things (oil pressure, temp etc, should be on the engine battery. and have no reason to be unswitched. infact they should probably be ignition controlled.




the bilge pump and high water should be on house unswitchd.

This! I had my engine panel wired to my house batteries which powers gauges/alarms and.....wait for it...Glow plugs!!!
I ended up learning the hard way that this was not a great configuration. Had house batteries that were failing and was unable to start my boat. Determined that weak house batteries weren't pumping enough juice to glow plugs. Would have never known and likely never had a problem had house batteries been healthy.
But.....in my mind, having glow plugs underpowered effectively produces the same result as a starter that's underpowered...no start! Luckily I was able to work through the problem with some annoyance rather than being thrust into a dangerous situation. Could have very well put me in a dangerous situation had circumstances been different though.

[Sandero]

These always on should not drain your house bank.... unless you have no charging... as in solar, wind or shore power.... and leave the boat for a long time. It doesn't take much in solar to supply what the always on consume... unless you have a bilge pump which draws a lot and runs a lot. Items such as the Link battery monitor draw little and usually are powered by the House bank.

I vote house.