Battery monitor

[Fascadale]

I live in dread of my (boat) batteries going flat

I have two batteries (one new, one two years old), an alternator on my 20hp engine, a voltmeter, and the usual Off, 1, 2, 1+2, isolator switch.

I use battery 1 for starting and battery 2 for every thing else. When the engine is on I have the switch at 1+2. I am very miserly with electricity often sailing with the GPS and VHF off (not much use in an emergency I hear you say)

With my sketchy understanding of electrical stuff I think (Prob. wrong) the voltmeter only gives an indication of battery condition while it is actually being charged. Around 14 good, less than 11 bad.

As far as I know with my present system I don't know what the rate of discharge is ( with the engine off) or what is left in the batteries (in amp hours)

I'm thinking of getting a Nasa battery monitor.

Will such a device reassure me as to the state of the batteries. Will it tell me how much is left in each battery or can it only tell me whats in the combined pair ?

Good sailing

 

[muckypup]

Only the combined pair - ie any battery bank you have connected in parallel. Good units though.

S.

 

[KenMcCulloch]

[ QUOTE ]



With my sketchy understanding of electrical stuff I think (Prob. wrong) the voltmeter only gives an indication of battery condition while it is actually being charged. Around 14 good, less than 11 bad.



[/ QUOTE ]
Dear Ockle
Voltage at rest (an hour or two after you have stopped charging) will in fact give you a fair idea of your battery's state (or batteries' states) of charge. 12.6V is fully charged, 12.2V 50% discharged. Just carry a multimeter and check your battery from time to time. Practice manoeuvreing under sail so that if you ever have an engine failure you can cope. Don't worry about the GPS and the VHF flattening your engine battery, they probably draw about an amp together unless you are transmitting so with a 100Ah battery you could leave them switched on for a couple of days and still only go down to 12.2V/50% charge. Enjoy your sailing and don't waste your money on a battery monitor. Buy a bigger battery instead if you have room!

 

[pvb]

The Nasa BM-1 can only monitor 1 battery (or 1 bank). However, if you are using Battery 1 for starting, selecting 1+2 when your engine's running, and switching to Battery 2 when you turn the engine off, then your Battery 1 should always be charged enough to start the engine. On this basis, having a Nasa monitor connected to Battery 2 will enable you to keep an eye on the state of your domestic battery.

As an aside, simple voltmeters often draw quite a significant current, so are best disconnected when not in use.

 

[andy_wilson]

The voltmeter gives an indication of the the alternator condition when charging, and also tells you how many rpm are needed to get 14V or so.

When the batteries are rested and with no load it will tell you if they are charged (about 12.6v) or flat (about 11.6v) - but you shouldn't go there, recharge at 12v (50%) if you want them to last.

 

[ChrisE]

We have an amp counter. Starts at 0 and goes negative as the amps are used. Not an absolute measure but combined with a voltmeter a useful indicator of the state of the batteries.

We found it an absolute godsend when long distancing, we had a rule of thumb to run the engine whenever we had used 100 amps (across three 110 ah batts).

 

[PIGLETSDREAM]

Not really understanding electrics i can't give an answer but, I was at Nassa last week, sorting out my Navtex and got into conversation with the engineer about the Battery Monitor and he said that it could be wired for two batteries and that they would give instructions if asked

 

[pvb]

Nasa BM-1...

[ QUOTE ]
Not really understanding electrics i can't give an answer but, I was at Nassa last week, sorting out my Navtex and got into conversation with the engineer about the Battery Monitor and he said that it could be wired for two batteries and that they would give instructions if asked

[/ QUOTE ]Yes, it can be wired to monitor 2 or more batteries connected as 1 bank, as long as the bank isn't bigger than 600/650/999 Ah (depending on which bit of the Nasa website you believe).

 

[Chris_Robb]

I have just added a Nasa BM1. I can't understand now why I never fitted one before. I can now see at a glance the rate of discharge with lights fridge, nav equipment, giving you (and SWMBO) an accurate picture of consumtion of each unit. In the case of SWMBO makes her see that lights left on all oevr the shop means more motoring the next day (hurray she says!)

I take it you are not on shorepower. The other usefull thing that the BM-1 does is to show clearly how much is going back intio the battery. When I first installed the unit, my battery voltages were being raised to 14.2 V. The ampage from the 50amp alternator started at 7-10 amps, and soon decended to about 3 amps, well before the batteries were full. So I added a sterling alternator regulator. This boosted the charge to 14.8, and for the first 15 minutes or more, the alternator outputs 45amps, decending to about 15amps before going into float when full and reducing volts to 13.8.

I was frankly gobsmacked at the difference. However now the worry is - how hot is the alternator getting, will it blow up under the pressure. So I intend to tape the heat sensor on my multimeter to the alternator for a few weeks, and just monitor the temp that it runs at. I actually wished that I had installed the advance form of regulator which shuts the alternator down until the heat becoems acceptable again. I suspect this would be essential in the Med.

 

[tome]

Suggest that as an alternative to the NASA you look at the Link 20 which monitors 2 independent banks. We have had one for the past 5 years and it's a godsend for long distance cruising

 

[pvb]

Overkill...

It's an excellent bit of kit but, at £280, the Link 20 is perhaps a bit over the top for a boat with only 2 batteries. The money would be better spent on a cheaper monitor and extra batteries.

 

[NPMR]

We have 1 x Monitor wired into the 'house' battery. It tells me at a glance where we are at and reminds to get those lights "OFF"!

Engine starting battery is monitored if you want but we have lower amp-hour capacity for engine battery so you would need to keep re-programming it, if I understand the manual properly.

With a Sterling Regulator, I'm finding we are not getting Low Battery warnings any more from the GPS, so it feels like it's working.

 

[Oldhand]

[ QUOTE ]
Dear Ockle
Voltage at rest (an hour or two after you have stopped charging) will in fact give you a fair idea of your battery's state (or batteries' states) of charge. 12.6V is fully charged, 12.2V 50% discharged.

[/ QUOTE ]

Ummm, 12.6v is a long way from fully charged, should be at least 12.8v unless there has been something wrong with all my boat batteries over dozens of years...

 

[Gumpy]

Personally I use a smartgauge from here:

http://www.smartgauge.co.uk

Only 2 wires to each battery bank ( via a fuse ) no shunts or heavy wiring, gives capacity left in the house batteries and voltage in the start battery.

Excellent piece of kit.

Julian

 

[KenMcCulloch]

[ QUOTE ]
[ QUOTE ]
Dear Ockle
Voltage at rest (an hour or two after you have stopped charging) will in fact give you a fair idea of your battery's state (or batteries' states) of charge. 12.6V is fully charged, 12.2V 50% discharged.

[/ QUOTE ]

Ummm, 12.6v is a long way from fully charged, should be at least 12.8v unless there has been something wrong with all my boat batteries over dozens of years...

[/ QUOTE ]
You may well be right, I am no expert but I am quoting figures from a standard text. The point remains however that resting voltage is a good indication of charge state; at a little less than 12v there's very little left, and at something less than 13v the battery is charged to capacity. My real point is that Ockle is worrying unnecessarily; so long as he keeps his starter battery charged he can run the domestic battery down quite a bit, quite often and not worry too much.

 

[Phoenix of Hamble]

I too fitted a NASA monitor recently..... great bit of kit for the price.... as you say... it really lets you know what kit onboard hits you, and what doesn't..... its a bit scary when you fire up the Eberspacher!!!!!!

 

[shamrock]

Re: Overkill...

Our Link 2000 is superb but yes, overkill for a small boat so recommend the NASA kit there.

I've become a total amps-czar, as I can lie on the settee berth, reading my book, and glance over at the monitor showing -2.2 and shout 'who's left the light on in the heads again?!' at the kids.

And you quickly see that all the instruments, radar, CD player etc are nothing compared to the fridge.

 

[William_H]

Re: Overkill...

Going back to the original poster. Don't worry...........
You apparently have a simple electrical system ie no fridge.
It is highly unlikely you would discharge the domestic battery over one on 2 nights of camping. You obviously understand the concept of isolation of your engine battery. So engine battery should never be discharged.
If as will eventually happen your engine battery does die you still have the doemestic battery most likely with enough charge to substitute for the engine battery or to help it to start the engine.
You should try starting on the domestic battery alone occasionally.

All this and you have sails to get you home..

Compared to your car you have multiple back ups so dont worry....

olewilll

 

[BrendanS]

Re: Overkill...

[ QUOTE ]
Compared to your car you have multiple back ups so dont worry....

[/ QUOTE ]

Some cars are pretty sophisticated these days, and do have multiple batteries. If the primary starting battery doesn't start the engine, you turn the key the opposite way for a few seconds, and the secondary battery kicks in.

 

[Chris_Robb]

Only draw back is the 100 amp shunt - I gather that forgetting to change the battery over from domestic to engine could cause the shunt to burn out on firing up the starter motor