Sailingsaves
Well-Known Member
Does anyone use a device that detects when their battery (or bank) gets to a low voltage, say 12.4volts and emits a warning and /or disconnects battery from load to prevent damage to battery?
battery over-discharge protector?
- Thread starter Sailingsaves
- Start date
rogerthebodger
Well-Known Member
That's what the "Load" connection on a solar regulator is supposed to do but they never have the current carrying capacity for any real use. The Danfoss fridge compressor also has that built in.
prv
Well-Known Member
I don't, but they do exist. Often sold as an item related to fridges, since for many people that's a major load and it's also not the end of the world if it gets disconnected for a while.
Pete
Pete
macd
Well-Known Member
Trouble is, 12.4V ain't low. It's about 30% discharged with no load. With, say, a 20A load for just a few minutes, it could even be the best part of fully charged. I suspect that's why you only normally encounter them attached to particular bits of kit, as Rogershaw mentioned: they probably need to be load-specific.
In your case, sailingsaves (you have just the one battery, I think?), you'd be in danger of turning everything else off when you started the engine, perhaps even including the starter motor...
In your case, sailingsaves (you have just the one battery, I think?), you'd be in danger of turning everything else off when you started the engine, perhaps even including the starter motor...
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GHA
Well-Known Member
No but could have, openplotter running on a raspberry pi could do that. Tricky though, if it's an intermittent load like a fridge then you might want to average up the voltage over half an hour or whatever to get a more realistic handle things.
Any more detail about what you want to do?
PabloPicasso
Well-Known Member
My Garmin chart lotter displays the battery voltage and beeps at a preset (but adjustable) level. It doesn't stop the discharge, just sounds a warning. Likely many plotters have thus feature. It was what I relied upon until I recently upgraded to a dedicated start battery, which is possibly the best answer really.
The battery, wiring, mega fuses, and VSR all cost a tad under £150. Well worth the expense.
The battery, wiring, mega fuses, and VSR all cost a tad under £150. Well worth the expense.
RichardS
N/A
I've got one that came installed with the boat. It says "Low Battery Warning" on the panel and there's a buzzer which sounds. I think it also disconnects the battery at some point but I've never taken things that low. I think the buzzer sounds at around 11.5V but I only ever hear it if I switch off the 12V master switch on the panel with other equipment running. As the voltage dies away it gives a short blast and then croaks.
I've no idea where it actually is. Presumably behind the panel near the buzzer but I've never looked for it.
Richard
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halcyon
Well-Known Member
Not a new thing back in 1982 http://www.kddpowercentre.co.uk/data/P4000_82_lit.pdf used to be standard on Westerlys and Sealine and others during the 1980's / 90's.
For normal use a voltmeter will do, 50% level, rested battery recharge at 12.3/12.4, battery in use 11.9 / 12.0 volt, it will not kill the battery going to 40%. If you have a big inverter, then a monitor that drops it out with audio is a good thing.
Brian
Hadenough
Well-Known Member
Sailingsaves
Well-Known Member
I had to sell my boat. I just tinker with windturbines and solar panels and things at the moment.
The device I have in mind can be set up with a 15 second delay.
So, as you start your engine (voltage may drop to 11.6 volts or whatever whilst cranking), but device wont sound alarm or disconnect battery.
I am thinking of deepcycle leisure batteries. They like to be charged to 13.6 volts-ish and even though they are more robust than other batteries, they still do not like to be deeply discharged.
The device I have in mind can be set to disconnect the battery at a voltage you choose.
My mate found his batteries down to 7 Volts - that would shorten their longevity. The device would have stopped whatever the drain was (lights left on I think).
I just wondered how prevalent these things were.
Me, I am currently making and testing things and using a leisure battery to power things in the garden (very slow gradual drain) and I don't want to drain the battery below 12.4 volts (simply because I want it to last a long time).
I understand for boat users that they may wish to lower the cut-off voltage; one wouldn't want to lose a chartplotter at 12.2 volts when negotiating some rocky passage.
Thanks.
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macd
Well-Known Member
Our deep cycle jobs like to be charged at up to 14.8V and floated at 13.4. But, like most, they drop to around 12.7 fairly quickly if rested. The voltage just off charge is meaningless.
Sailingsaves
Well-Known Member
All sorts of batteries out there before we even talk about agm, gel, etc.
I have a Camden Boss, about 4 years old, never charged above 13.6 as per spec and never discharged below 12.2 Rests at 12.8 to this day.
Another special battery (over £400 new, but I bought second hand for less than £90) rests at 12.85 for over a month (it weighs so much I can hardly lift it and I'm no wimp) and it states on it, float charge, 13.63Volts.
I like to look after my batteries and have been called anally retentive often.
Jokani
Well-Known Member
I purchased one of these last month to install this coming winter http://www.ebay.co.uk/itm/141107864386
Sailingsaves
Well-Known Member
I looked at those (not bought or used one). Hope it is good for you. Bit pricey for my pocket at moment though.
Lon nan Gruagach
Well-Known Member
If its tinkering with electronics thats fun then heres some ideas..
Battery voltage is only half the story, measure current too.
Allocate 2 load classifications,or more for that matter: Always on, really should be on and trivial, sacrifice them according to battery state.
Always on: bilge pump, I would rather a battery breathed its last trying to keep the boat afloat.
Really should be on: navigation toys GPS, chart plotter.
Trivial: the fridge
Battery voltage is only half the story, measure current too.
Allocate 2 load classifications,or more for that matter: Always on, really should be on and trivial, sacrifice them according to battery state.
Always on: bilge pump, I would rather a battery breathed its last trying to keep the boat afloat.
Really should be on: navigation toys GPS, chart plotter.
Trivial: the fridge
Sailingsaves
Well-Known Member
Agree.
Everyone should have a watt meter - cheap as chips on ebay.
My drop tester only cost £20 too and all my mates get to use it to see if their batteries are ok.
One mate had 12.7 volts, but ZERO current: he even shorted the battery to see if it would spark - zilch - drop tester screamed from its dial "Replace !"
Fendant
Well-Known Member
This is the same one I have installed this summer after my fridge killed two very expensive AGM's.
This battery guard has an adjustable cut out voltage. The fridge has a built incut out voltage at 10.4 V.
However AGM Batteries are already dead like Elvis at 10.5 V. Here is the table for AGM,s, discharging below 50% severly affects the battery life:
Volt State of Charge
12.6 100%
12.5 90%
12.42 80%
12.3 70%
12.2 60%
12.05 50%
11.9 40%
11.72 30%
11.5 20%
11.3 10%
10.5 0% !!
This battery guard has an adjustable cut out voltage. The fridge has a built incut out voltage at 10.4 V.
However AGM Batteries are already dead like Elvis at 10.5 V. Here is the table for AGM,s, discharging below 50% severly affects the battery life:
Volt State of Charge
12.6 100%
12.5 90%
12.42 80%
12.3 70%
12.2 60%
12.05 50%
11.9 40%
11.72 30%
11.5 20%
11.3 10%
10.5 0% !!
maby
Well-Known Member
I have one which I built myself using Arduino components. It has three switched circuits that can be prioritised - as battery voltage drops off, it starts shedding load according to the configured rules. It stays in circuit itself until the battery voltage gets really low - sub-10v - and if the voltage picks up again, it will power up the loads in the defined order of priority.
lw395
Well-Known Member
Depending on the size of battery and the current drawn, the voltage drops.
Take a 50% discharged battery, take 10A from it and see the volts drop.
So you have to be careful with low voltage shut-down, that it doesn't shut down as soon as the load comes on and then rest as soon as it's stopped it.
Some bits of electronics and some other bits of hardware (eberbasto...!) don't like being shut down by removing the supply.
There's a balance between spending money on control and monitoring, vs buying a big enough battery bank and not having the problem. YMMV....
