Leisure battery cut off device

[ppc]

Is there a way to have leisure batteries automatically isolated when they fall bellow a specified charge? Having the lights go out would be a good fail-safe to know when to charge them up again. Our setup is as follows:

BMV-501 battery monitor

Victron energy multi plus inverter

EP Solar, with MT50 display

 

Many thanks in advance

 

Pete

 

[Robbo]

Just now, ppc said:

Is there a way to have leisure batteries automatically isolated when they fall bellow a specified charge? Having the lights go out would be a good fail-safe to know when to charge them up again. Our setup is as follows:

Victron do a battery protect...

https://www.victronenergy.com/battery_protect/battery-protect

[Alan de Enfield]

7 minutes ago, ppc said:

Is there a way to have leisure batteries automatically isolated when they fall bellow a specified charge? Having the lights go out would be a good fail-safe to know when to charge them up again. Our setup is as follows:

BMV-501 battery monitor

Victron energy multi plus inverter

EP Solar, with MT50 display

 

Many thanks in advance

 

Pete

 

This may not be what you want to hear, but it is not difficult to 'take responsibility' for your actions, you already have the equipment to tell you what you need to know, all you have to do is look at it.

Why involve further complicated equipment that is just another potential fail point in the system ?.

 

So, the lights, fridge, water pump & TV goes off whilst watching the 10 O'clock news, what are you going to do ?

You cannot run the engine, you have no solar power just go to bed and wait until the next morning.

 

Alternatively - 'manage' (in the proper sense of the word) you electrical consumption and production.

[ppc]

Much appreciated Robbo.

 

Pete

[Machpoint005]

3 hours ago, Alan de Enfield said:

So, the lights, fridge, water pump & TV goes off whilst watching the 10 O'clock news, what are you going to do ?

You cannot run the engine, you have no solar power just go to bed and wait until the next morning.

Read a book by candle light!

 

Seriously, I agree that some sort of energy audit, even an informal one. is a must.

[David Mack]

The rule of thumb is not to take the battery below 50%. But it is only a rule of thumb - a compromise between the fuel costs and engine wear and tear of recharging and the reduced battery life of not doing so. So the occasional dip below 50% won't matter, and will be balanced by those occasions when you don't let the battery get that low. 

[ppc]

Sounds sensible. Would you say around 12v mark represents 50% discharge? 

 

We've turned off our fridge and are very sparing on lighting (all LED). The biggest draw is the webasto which we usually programme to come on in the morning, so we figure that it's important to ensure well-charged batteries before bed. This often means 1 or 2 hrs charging using engine/alternator in the evening before 8pm. 

 

In addition, we're trying to work out optimal  running time and revs when running the engine. We currently have 3 Numax 110ah sealed leisure batteries. Any suggestions would be most welcome.  

 

Thanks

[Jess--]

the problem you will run into if you disconnect batteries when they fall below a specified voltage is that once you have cut them off the voltage will rise again (which may make your system reconnect)

[Alan de Enfield]

38 minutes ago, ppc said:

Sounds sensible. Would you say around 12v mark represents 50% discharge? 

12.2 volts = 50%

[Tony Brooks]

2 hours ago, Alan de Enfield said:

12.2 volts = 50%

 

That is more or less OFF LOAD.

 

Seriously, I am with Alan. get used to monitoring the voltage at odd times through the day/evening (like when you go to the loo) plus first thing in the morning while it is still dark so the solar is not giving a false high reading and you will soon get a good idea about when you need to charge or stop using  electricity. Likewise use the ammeter function to tell you when the batteries are more or less fully charged (current flow at 14V+ of less than 1 to 2% of battery capacity.

 

One thing you should never do is put any credence if the Ah left or percentage of fully charged figures the meter gives you. In most boaters' hands it tell lies and ensures you wreck batteries.

[Richard10002]

If you are charging you batteries properly, and they are falling below 50% regularly, then you probably haven’t got enough capacity. This could be because 115Ah isn’t enough to last you between charging to 100%, or because your batteries are sulphate, and their capacity is much less than you think/hope.

 

Using the back of a cigarette packet, it seems that most of us use between about 70Ah and 120Ah a day. Presumably the former is quite frugal, and the latter the opposite, (profligate?).

 

If you are somewhere in between, say 100Ah, you will need to be charging to 100% each day, which probably takes much longer than you think, at least 3 or 4 hours, even with a relatively high Amps charger, and likely more.

[WotEver]

1 minute ago, Richard10002 said:

If you are somewhere in between, say 100Ah, you will need to be charging to 100% each day, which probably takes much longer than you think, at least 3 or 4 6 hours, even with a relatively high Amps charger, and likely more.

Fixed that for you. 

[Tony Brooks]

1 hour ago, WotEver said:

Fixed that for you. 

I would have made that 10 to 12 ----------------------------------- but who knows in reality unless the amps are monitored.

[WotEver]

1 hour ago, Tony Brooks said:

I would have made that 10 to 12 ----------------------------------- but who knows in reality unless the amps are monitored.

Indeed. The length of time is always ‘more than you thought it would be’. 

[MtB]

3 hours ago, Richard10002 said:

 

If you are somewhere in between, say 100Ah, you will need to be charging to 100% each day, which probably takes much longer than you think, at least 3 or 4 hours, even with a relatively high Amps charger, and likely more.

 

I was reading battery university yesterday, the article I was reading about lead carbon batteries stated specifically that it takes 14 hours to charge a LA battery from 0% (10.5v) to 100%. 

Quite a precise claim, I thought.

[WotEver]

7 minutes ago, Mike the Boilerman said:

 

I was reading battery university yesterday, the article I was reading about lead carbon batteries stated specifically that it takes 14 hours to charge a LA battery from 0% (10.5v) to 100%. 

Quite a precise claim, I thought.

Oddly precise, yes. We’re talking about starting from 50% or higher though. 

[MtB]

10 minutes ago, WotEver said:

Oddly precise, yes. We’re talking about starting from 50% or higher though. 

 

In which case I'd say the ten hours it takes my batteries is about right. 

[Alan de Enfield]

A couple of years ago we were moored up close to a boat whose engine kept starting, running 15-20 minutes and stopping - and hour or so later it started up again ……….. repeat.

 

It turned out that somehow there was a voltage sensor that was connected to the engine starter - when it sensed the voltage on the leisure batteries drop to a pre-set level it started the engine until it sensed a pre-set 'higher' voltage and switched the engine off.

No 8 to 8 rules for him - the boat decided when it would start the engine.

 

I think the OP would be interested in something like that - even takes away the inconvenience of having to get out of your chair to press the 'start' button.

[dor]

12 hours ago, ppc said:

 

In addition, we're trying to work out optimal  running time and revs when running the engine. We currently have 3 Numax 110ah sealed leisure batteries. Any suggestions would be most welcome.  

 

Thanks

You really need an ammeter if you haven't got one for two main reasons.  Firstly, you will notice that the current drops surprisingly quickly when you start charging.  A 90A alternator might start giving 80+  into 50% discharged batteries at say 1,800 rpm, but will drop rapidly to say 50 amps.  It will then drop more slowly to say 30 amps.  By this time you may only need 1,200 rpm, so reduce speed of the engine while watching the ammeter until the amps start dropping.   After another hour say, it may only be putting in 18 amps and you can reduce the engine speed to say 900 rpm/tickover and the amps will gradually creep downwards.  When you get to about 1% of battery capacity, ~3 - 4 amps for a 4 x 100 A bank (don't forget you are charging your starter battery as well), you can consider the batteries fully charged.  This will take several hours.

These figures will vary from boat to boat but are typical figures for a modern Vetus/Beta type engines with a regulator regulating to 14.4 - 14.6 amps.

Edited November 7, 2018 by dor

[blackrose]

20 hours ago, Alan de Enfield said:

This may not be what you want to hear, but it is not difficult to 'take responsibility' for your actions, you already have the equipment to tell you what you need to know, all you have to do is look at it.

Why involve further complicated equipment that is just another potential fail point in the system ?.

 

So, the lights, fridge, water pump & TV goes off whilst watching the 10 O'clock news, what are you going to do ?

You cannot run the engine, you have no solar power just go to bed and wait until the next morning.

 

Alternatively - 'manage' (in the proper sense of the word) you electrical consumption and production.

I tend to agree. If one isn't going to look at one's battery monitor then there's not really much point having it. On the other hand if you do use your battery monitor and charge the batteries accordingly, you won't need any cut-off device.

 

Why complicate matters unnecessarily?

Edited November 7, 2018 by blackrose

[Robbo]

17 minutes ago, blackrose said:

I tend to agree. If one isn't going to look at one's battery monitor then there's not really much point having it. On the other hand if you do use your battery monitor and charge the batteries accordingly, you won't need any cut-off device.

 

Why complicate matters unnecessarily?

The BMV also has audible alarms as well as a relay output.  If the OP just wants to be notified when the batteries are low then this should be used.   The battery protect device I linked too is really for protecting the battery from serious undercharging when something is amiss not for day 2 day stuff.

[cuthound]

10 hours ago, Mike the Boilerman said:

 

I was reading battery university yesterday, the article I was reading about lead carbon batteries stated specifically that it takes 14 hours to charge a LA battery from 0% (10.5v) to 100%. 

Quite a precise claim, I thought.

 

Sounds about right.

 

At the dawn of my career, I had to give the telecoms batteries in my care a "conditioning cycle" every 2 years by discharging the battery at the 10 hour rate until the first cell reached 1.75 volts and then immediately recharging until the tail current and sg's had been stable for 3 consecutive half hourly readings. The total exercise used to take 24-26 hours on average.

[Sea Dog]

11 hours ago, Mike the Boilerman said:

 

I was reading battery university yesterday, the article I was reading about lead carbon batteries stated specifically that it takes 14 hours to charge a LA battery from 0% (10.5v) to 100%. 

Quite a precise claim, I thought.

I think if I found my batteries were at 0% the best use of those 14 hours might be finding the cause... and sourcing replacements!

 

[MtB]

44 minutes ago, Sea Dog said:

I think if I found my batteries were at 0% the best use of those 14 hours might be finding the cause... and sourcing replacements!

 

 

Not if you had lead carbon batteries. They don't mind with this type of use apparently. 

 

 

[Sea Dog]

1 minute ago, Mike the Boilerman said:

 

Not if you had lead carbon batteries. They don't mind with this type of use apparently. 

 

 

Fair call. Do any amongst us have those?