Low volt sensor for 12 volt cooler

Refueler said:
Its strange that most items I see and use have a too low factory set cut off in my mind. I suppose they set it based on a really good battery .. easy starting engine !! Maybe a Moped ?
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I think that is because they are designed save the battery from a disastrously deep discharge rather than to retain a relatively high state of charge for other equipment.
 
VicS said:
I think that is because they are designed save the battery from a disastrously deep discharge rather than to retain a relatively high state of charge for other equipment.
Click to expand...

The one you mentioned with 11.6v cutoff represents an 80% discharge on most lead acid batteries, which I'd say was far too deep for a decent battery life.
 
I installed the cool box and the cut off device as recommended. It cuts in at 13 V & off at 12.9V so it will not flatten the batteries but will come on when shore power turns on the charger or the engine is powering the alternator.

All as intended----------------------BUT
The cool box, ( which has a remarkably silent fan & does an excellent job of cooling) does not have a shut off element when a certain minimum temp is reached in the way a fridge has. I have installed a switch to it & can, if I wish , turn it on & of manually but that was not the original intention.
The problem is the shore power charger.
This is a Dolphin 15 amp triple stage one. So when I get to port & plug in it immediately starts charging atapprox 14.7 V (forget exact figs so bear with me on this one) & because it is a max power its fan comes on. THIS IS NOISY. It normally runs for max half an hour if I have not been motoring much. Then when the charger goes on to a mid level charge at approx 13..8 voltage the fan goes off. later on the charger goes to float at about 13.3V so the cool box would be expected to work. HOWEVER. If ( without the cool box working) I operate a hot water tap the charger immediately responds & the fan comes on to react to the current used & picks up to 14.7V. This is not a problem as when the tap goes off the fan goes off. BUT with the cool box drawing 3.5 amps the charger (&fan) permanently operates at 14.7 V .This means it is stuffing over 14 volts into already fully charged starter and domestic batteries.
So my query is:-

If I leave it like this all night ( with noisy fan running!!!) will I cook the domestic & starter batteries, or will the fact that the cool box is using the 3.5 amps thus using the extra power stop that happening?
 
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I am surprised you did not realised that these Peltier element coolboxes run continuously ...
Compressor fridges are much better .... but very much more expensive ... different ballpark altogether, They are thermostatically controlled and although draw more current when actually running over ,say a day the average current , and hence the Ah used , is significantly less.

It seems that our battery charger is not one which is designed to supply a load while charging the battery in the normal way Some chargers will continue to supply a float charge to the battery while supplying a load ( dunno how they do that though )
Yours goes into or stays in absorption mode if a load draws several amps from it.

Some chargers also heve a night ( silent) mode
 
The battery cut off devices on Ebay from China look fine for the job however do make sure they have an adjustment for both turn on and turn off voltage. Electronic design wise it is simpler to just have a single cut in cut out voltage bu this can result in relay chatter as the battery voltage rises when the load is disconnected so turning the fridge on again only to have battery voltage fall so the chatter. Thsi one claims to have both off and on voltages adjustable. 12V Battery Low Voltage Cut off Automatic Recovery Under-voltage Switch Module | eBay
 
William_H said:
The battery cut off devices on Ebay from China look fine for the job however do make sure they have an adjustment for both turn on and turn off voltage. Electronic design wise it is simpler to just have a single cut in cut out voltage bu this can result in relay chatter as the battery voltage rises when the load is disconnected so turning the fridge on again only to have battery voltage fall so the chatter. Thsi one claims to have both off and on voltages adjustable. 12V Battery Low Voltage Cut off Automatic Recovery Under-voltage Switch Module | eBay
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That is not the issue. The cut off device I have, works perfectly ( recommended on this forum) & I have adjusted it to go on at 13V and off at 12.9
The issue I am concerned with, is whether the charger will cook the batteries if constantly charging at over 14v or if the load applied by the cool box is stopping the batteries being cooked
 
I think DB is finding the modern day battery charger problem.

Smart chargers are fine when connected as designed - but introduce an extra element and they start to act strange ... many in fact don't even start up !

If this was my setup ... I would have an old fashioned basic charger of about 4A .... (this is less than the Peltier box requires ... many are 5A or more .. mine can draw up to about 8A ... ) .......
It sounds daft I know but bear with me.

Lets say you have the 'smart charger' and can whack out 10A or more .... I would put a switch in that allows me to choose that one or a basic 4A old fashioned charger - depending on state of batterys when I first go alongside. But most time the smart charger would be disabled..... there for really serious charging when needed.

Connect up shore power with the old low amp charger .... which is less than the coolbox uses ... this means the battery will slowly drain down till the voltage cut off actions. The old charger because it doesn't care about other items and just pumps out regardless - will then have all its 4A charging battery back up again ...
Basically then you have no fear of cooking the batterys .. because as soon as you hit 13V again .. coolbox cuts in .... taking all the 4a + balance from battery.

That's my suggestion ...
 
Daydream believer said:
That is not the issue. The cut off device I have, works perfectly ( recommended on this forum) & I have adjusted it to go on at 13V and off at 12.9
The issue I am concerned with, is whether the charger will cook the batteries if constantly charging at over 14v or if the load applied by the cool box is stopping the batteries being cooked
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The voltage mentioned earlier, 14.7, seems a little high, but since you made a reservation about the exact figure, my view is this:
The batteries will not be damaged from the above situation if it occurs now and then, however permanently or often applying absorption voltage (≈14.4) to already fully charged batteries will shorten their lifespan, especially if they are AGM or MF.
 
BabaYaga said:
The voltage mentioned earlier, 14.7, seems a little high, but since you made a reservation about the exact figure, my view is this:
The batteries will not be damaged from the above situation if it occurs now and then, however permanently or often applying absorption voltage (≈14.4) to already fully charged batteries will shorten their lifespan, especially if they are AGM or MF.
Click to expand...

Any rise in temperature of a WET acid battery will cause 'boil-off' ....

My post of using a lower rated old fashioned charger is based on it NOT being able to keep up fully with the coolbox amp demand. It also does not have smart circuitry that can cause it to act strangely.

I have a solid state split device on my boat with a timer on the mains. It gives 2 hrs a day charge for 5 days out of 7. If I connect a modern smart charger - it will charge then cut off - and not restart - the charge relay causes it to drop out.
But connecting an old fashioned 4A non smart charger and she sits there happily charging away switching on / off as necessary. It never overloads / cooks the batterys ... in fact as battery voltage rises - the old fashioned charger drops back in amp rate ...
In know its not quite same as the coolbox - but just shows that smart chargers are great when they are setup as designed - but introduce another factor and they really do not like it.
 
William_H said:
The battery cut off devices on Ebay from China look fine for the job however do make sure they have an adjustment for both turn on and turn off voltage. Electronic design wise it is simpler to just have a single cut in cut out voltage bu this can result in relay chatter as the battery voltage rises when the load is disconnected so turning the fridge on again only to have battery voltage fall so the chatter. Thsi one claims to have both off and on voltages adjustable. 12V Battery Low Voltage Cut off Automatic Recovery Under-voltage Switch Module | eBay
Click to expand...

The item you link to is the next step up from the item I linked to. Mine only has the TURN OFF low voltage adjustment.

The item you link to has the TURN ON adjustment as well ..... so it will reconnect once voltage rises to the set point.

It still does not solve DB's question of how to avoid 'cooking' his batterys ....... I would suggest he's looking for a way to cut off charging once batterys get to full charge and for the charge to restart once it drops ... and not just trust the charger
 
Traditionally, a lot of systems run at about 13.7V when mains is present. Battery is float charged, regulated 13.7 runs all the loads.
That's very common in things like alarms where the mains is expected to be present 99% of the time.

If you want to set the low voltage cutoff for a reasonable state of charge of the battery, bear in mind the discharge rate will reduce the voltage, e.g. 12.0V is about 50% SOC at C/10, but only 15% SOC at C/100.
You can do all this and more with a comparator chip and maybe a few diodes, or a small micro such as an arduino.
Clarifying exact wishlist of requirements is the bigger problem?
 
lw395 said:
Traditionally, a lot of systems run at about 13.7V when mains is present. Battery is float charged, regulated 13.7 runs all the loads.
That's very common in things like alarms where the mains is expected to be present 99% of the time.

If you want to set the low voltage cutoff for a reasonable state of charge of the battery, bear in mind the discharge rate will reduce the voltage, e.g. 12.0V is about 50% SOC at C/10, but only 15% SOC at C/100.
You can do all this and more with a comparator chip and maybe a few diodes, or a small micro such as an arduino.
Clarifying exact wishlist of requirements is the bigger problem?
Click to expand...

Trouble is we already know from DB's previous - he wants simple solution without need to know electronics. Which limits ideas ...

I must admit - simple appeals to me as well !!
 
Refueler said:
Trouble is we already know from DB's previous - he wants simple solution without need to know electronics. Which limits ideas ...

I must admit - simple appeals to me as well !!
Click to expand...
Your idea ofan additional charger is not so bad. I think that I might be able to manage that. I can simple put a 240 v switche into the system & power up the main charger for a while each day or when I arrive in port & plug in the other charger once I am up to full power. If the domestics do run down the cool box will shut off & the start battery will also isolate via the VSR that i have betwen that & the domestics. The batteries are all AGM by the way
I now need a suitable charger that will not burn out on constant load & will just provide the 3.5 amps.
 
Daydream believer said:
I installed the cool box and the cut off device as recommended. It cuts in at 13 V & off at 12.9V so it will not flatten the batteries but will come on when shore power turns on the charger or the engine is powering the alternator.
All as intended----------------------BUT
The cool box, ( which has a remarkably silent fan & does an excellent job of cooling) does not have a shut off element when a certain minimum temp is reached in the way a fridge has. I have installed a switch to it & can, if I wish , turn it on & of manually but that was not the original intention.
The problem is the shore power charger.
This is a Dolphin 15 amp triple stage one. So when I get to port & plug in it immediately starts charging atapprox 14.7 V (forget exact figs so bear with me on this one) & because it is a max power its fan comes on. THIS IS NOISY. It normally runs for max half an hour if I have not been motoring much. Then when the charger goes on to a mid level charge at approx 13..8 voltage the fan goes off. later on the charger goes to float at about 13.3V so the cool box would be expected to work. HOWEVER. If ( without the cool box working) I operate a hot water tap the charger immediately responds & the fan comes on to react to the current used & picks up to 14.7V. This is not a problem as when the tap goes off the fan goes off. BUT with the cool box drawing 3.5 amps the charger (&fan) permanently operates at 14.7 V .This means it is stuffing over 14 volts into already fully charged starter and domestic batteries.
So my query is:-
If I leave it like this all night ( with noisy fan running!!!) will I cook the domestic & starter batteries, or will the fact that the cool box is using the 3.5 amps thus using the extra power stop that happening?
Click to expand...

14.7 volts for the absorption stage is rather high. It may be OK for lead calcium batteries but it is too high for other types. It would be unacceptable for Gel, AGM and sealed low maintenance batteries. Even with open flooded lead acid it would cause excessive gassing leading the need for frequent topping up. The gassing could cause the gas detector to alarm if not vented externally. This would be a nuisance , especially at night.

Your Dolphin charger should have several user selectable charging profiles. You could select one with a lower absorption voltage ( eg for FLA or for AGM ) You will still have the charger stuck in absorption mode rather than reducing to a float voltage of 13.2 or 13.7 depending on the battery type selected but maybe it will be a tolerable situation.

Your Dolphin charger may also have a "night mode" switch . This will allow the charger to operate at a lower maximum current without the fan running. Using the night mode option would solve the problem of the noisy fan at night.

The 3.5 amps taken by the coolbox will not be sufficient to prevent the batteries "overcharging"

If the above does not solve the problems try one of Refueller's novel solutions
 
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