Electrical 12v low voltage cutoff

[Crusty181]

Just for your info @Boots in Action, the 2x low voltage cutoffs I acquired create a noticeable drain on the battery. Ive alternate connected both of the boards straight to the end of the existing fridge lead, so theres's nothing new there aside for the LVC itself. The fridge connected to the end of that lead without the LVC, and turned off, draws zero from the battery. The LVC connected and powered up but the fridge not connected at all will eventually over time set off the low voltage alarm on my remote battery monitor which is connected to the cars battery.

The LVCs certainly do work, no question there but that comes with side effects. Also Voltage drop over the length of the wire wasn't something Id factored in, so the fine tuning needs adjusting for that slightly lower voltage at the LVC than at the voltage at the battery.

With life on pause Ive also acquired the off the shelf unit you have, I haven't tried that but I suspect it will do the same thing. It might pay to have a look at yours if your using it

 

[Boots in Action]

Just for your info @Boots in Action, the 2x low voltage cutoffs I acquired create a noticeable drain on the battery. Ive alternate connected both of the boards straight to the end of the existing fridge lead, so theres's nothing new there aside for the LVC itself. The fridge connected to the end of that lead without the LVC, and turned off, draws zero from the battery. The LVC connected and powered up but the fridge not connected at all will eventually over time set off the low voltage alarm on my remote battery monitor which is connected to the cars battery.

The LVCs certainly do work, no question there but that comes with side effects. Also Voltage drop over the length of the wire wasn't something Id factored in, so the fine tuning needs adjusting for that slightly lower voltage at the LVC than at the voltage at the battery.

With life on pause Ive also acquired the off the shelf unit you have, I haven't tried that but I suspect it will do the same thing. It might pay to have a look at yours if your using it

Thanks @Crusty181 for that feed back. I have only ever connected the LVC to a 12 volt battery at a no load voltage of 12.6 volts or close to that. For a load, I connected a 36w bulb (drawing 3A?) and watched the voltage drop to the low voltage setting I had set at 11.8 volts. It cut off the current at that level as it should. With the load still connected (but disconnected by the LVC box), I then connected a 15A "smart" charger and watched the result. Voltage rose steadily until the reconnect setting was reached plus about 0.2 volt when the box reconnected the load and the light was again lit. Voltage continued to rise until I switched off the charger at about 13.5 volts. Load still stayed connected as voltage fell and the whole process started again as expected. So I did not sense any problems.
But I did not check the current draw from battery to LVC box with NO LOAD applied. You have now given me a task and I will be right on it and let you know how it goes. Theoretically, current draw should be negligible as it is only sensing voltage, but happy to test carefully as always and advise accurate results. Stay tuned.

 

[Crusty181]

Thanks @Crusty181 for that feed back. I have only ever connected the LVC to a 12 volt battery at a no load voltage of 12.6 volts or close to that. For a load, I connected a 36w bulb (drawing 3A?) and watched the voltage drop to the low voltage setting I had set at 11.8 volts. It cut off the current at that level as it should. With the load still connected (but disconnected by the LVC box), I then connected a 15A "smart" charger and watched the result. Voltage rose steadily until the reconnect setting was reached plus about 0.2 volt when the box reconnected the load and the light was again lit. Voltage continued to rise until I switched off the charger at about 13.5 volts. Load still stayed connected as voltage fell and the whole process started again as expected. So I did not sense any problems.
But I did not check the current draw from battery to LVC box with NO LOAD applied. You have now given me a task and I will be right on it and let you know how it goes. Theoretically, current draw should be negligible as it is only sensing voltage, but happy to test carefully as always and advise accurate results. Stay tuned.

Im not driving this car much at present, so it can sit idle for upto 4 days. The voltage drop is happening slowly but surely over a few of days, but its siginificant enough to eventually set off the battery monitor

 

[Boots in Action]

@Crusty181 , state of battery capacity to carry "light?" load may have an effect. Just because battery is indicating "full" charge does not mean that all cells are the same or that complete "Absorption" stage was completed. If we are talking milliamps of around 10 or so, then there should not be a problem. However, if around 100 or so, that is a different story. My tests will confirm what is happening.
A recent example while charging my 7 year old AGM van battery on my 7 stage "smart" charger showed that even after the final stage (" Float or Maintain" had been reached) a certain amount of current was still flowing into the battery. In this last stage of "Float", input current pulsed at between 2.3 amps and 1.5 amps or less with voltage remaining at 13.7 volts. After 24 hours still on "Float" current had reduced pulsing down to as low as 0.06A to 0.005A. And yes, I have the time and equipment to do these checks. Interesting. There was also a recent article in our RACQ mag telling people that the vehicle alternator will NEVER fully charge your battery, no matter how far you travel or how long you run the engine. That as why "smart" chargers are so good with today's modern batteries.

 

[mikerezny]

Hi,
two tests need to be done. Both with no load applied.

The first is to measure the current drawn by the device when the battery voltage is over the LVC threshold.
The second is when the battery voltage is lower than the LVC threshold.
This should be easy enough to do if the LVC threshold of the device can be adjusted. Easier still if using a DC clampmeter.

If these currents are negligible, then the decreasing battery voltage is being caused by something else.

take care
Mike

 

[Crusty181]

Hi,
two tests need to be done. Both with no load applied.

The first is to measure the current drawn by the device when the battery voltage is over the LVC threshold.
The second is when the battery voltage is lower than the LVC threshold.
This should be easy enough to do if the LVC threshold of the device can be adjusted. Easier still if using a DC clampmeter.

If these currents are negligible, then the decreasing battery voltage is being caused by something else.

take care
Mike

Ill need to buy a clampmeter for that. Before I connected the LVC, the battery condition never changed over similarly log idle time periods, 4 odd days or so. I bought two different LVC circuits, a 10amp and 20amp. I didn't intend using both just the first one to arrive at that point because I intended going away. After the voltage drain of the 20amp, I swapped it over for the 10amp thinking maybe the 20amp was faulty or just rubbish, but got the same drain on the battery. I havent connected as yet the 3rd prefab unit that @Boots in Action has. Maybe that wont have the issue, but I suspect the circuitry would be the same. With the fuse on that fridge lead now removed the battery condition remains unaffected

 

[Boots in Action]

Hi,
two tests need to be done. Both with no load applied.

The first is to measure the current drawn by the device when the battery voltage is over the LVC threshold.
The second is when the battery voltage is lower than the LVC threshold.
This should be easy enough to do if the LVC threshold of the device can be adjusted. Easier still if using a DC clampmeter.

If these currents are negligible, then the decreasing battery voltage is being caused by something else.

take care
Mike

Yes Mike @mikerezny , gotta love that clamp meter!!!

 

[mikerezny]

Ill need to buy a clampmeter for that. Before I connected the LVC, the battery condition never changed over similarly log idle time periods, 4 odd days or so. I bought two different LVC circuits, a 10amp and 20amp. I didn't intend using both just the first one to arrive at that point because I intended going away. After the voltage drain of the 20amp, I swapped it over for the 10amp thinking maybe the 20amp was faulty or just rubbish, but got the same drain on the battery. I havent connected as yet the 3rd prefab unit that @Boots in Action has. Maybe that wont have the issue, but I suspect the circuitry would be the same. With the fuse on that fridge lead now removed the battery condition remains unaffected

Hi,

Do you have a normal digital multimeter that van measure current?
If so, take one of your uninstalled LVC units and measure the current though it when connected to a battery with no load connected.

Or with the fuse on the fridge lead removed, you can measure the current across the empty fuse holder.

take care
Mike

 

[Crusty181]

Hi,

Do you have a normal digital multimeter that van measure current?
If so, take one of your uninstalled LVC units and measure the current though it when connected to a battery with no load connected.

Or with the fuse on the fridge lead removed, you can measure the current across the empty fuse holder.

take care
Mike

Yes ive got a 10a meter, and ive just ordered a 100amp clamping meter too. Why not. Ill check it with the meter tomorrow.

 

[Boots in Action]

Yes ive got a 10a meter, and ive just ordered a 100amp clamping meter too. Why not. Ill check it with the meter tomorrow.

Hi @Crusty181 and @mikerezny , I did some preliminary testing this afternoon with a weak battery 12 volt. Here are the parameters:
Low voltage cutout setting...11.80 volts. Low voltage reconnect setting...12.50 volts. Load is a 36 watt incandescent bulb. Total load with voltage cutout in circuit is 3.35amps. Cutout unit has digital LEDs showing current voltage and also a undervoltage indicator light which comes on when battery voltage is below setting. These are included in the readings below:
With NO load and unit connected and LVR above setting of 12.5 volts... total current draw for unit is 0.034A @ 13.5 volts. (0.459w)
With NO load and unit disconnected by LVC as below setting of 11.80 volts.... total current draw for unit is 0.084A at 11.6 volts. (0.9828w)
Increased current draw when load disconnected by unit increased because extra warning light on .
In view of these figures being extremely low, I doubt that they would cause much voltage drop in a battery in good condition and fully charged to proper capacity. The 0.034 amps whist above LVR would never be a worry , and the 0.084A whilst load is sitting in disconnected mode would take a long time to discharge a good battery IMHO.
More testing with a better battery tomorrow to confirm these results. I think you must have other "ghost currents" causing your battery voltage to drop. Remember, lead acid batteries do lose their charge fairly quickly, unlike AGMs. What do you think@Crusty??

 

[mikerezny]

Hi,
assuming my arithmetic is correct. Based on measurements by @Boots in Action:

That is 0.82Ah per day when the LVC is ON (good voltage) and 2Ah per day when the load is OFF (low voltage).
In one month, with a good battery voltage, it is consuming 24Ah per month. i.e. 24% of a 100Ah battery

The self discharge rate for AGM is 1-2% per month. With a typical 100Ah battery that is between 1Ah an 2Ah per month.
Taking the average of 1.5Ah per month, that is 0.05Ah per day.

If the battery voltage is good, then the LVC depletes a 100Ah battery at a rate 16 times faster then the self discharge rate.
Once the battery is at low voltage, then it depletes a battery at a rate 40 times faster than self discharge.

If this is indeed the case, now wonder the battery is slowly going flat.
Good pick up @Crusty181 !

take care
Mike

 

[Crusty181]

Hi @Crusty181 and @mikerezny , I did some preliminary testing this afternoon with a weak battery 12 volt. Here are the parameters:
Low voltage cutout setting...11.80 volts. Low voltage reconnect setting...12.50 volts. Load is a 36 watt incandescent bulb. Total load with voltage cutout in circuit is 3.35amps. Cutout unit has digital LEDs showing current voltage and also a undervoltage indicator light which comes on when battery voltage is below setting. These are included in the readings below:
With NO load and unit connected and LVR above setting of 12.5 volts... total current draw for unit is 0.034A @ 13.5 volts. (0.459w)
With NO load and unit disconnected by LVC as below setting of 11.80 volts.... total current draw for unit is 0.084A at 11.6 volts. (0.9828w)
Increased current draw when load disconnected by unit increased because extra warning light on .
In view of these figures being extremely low, I doubt that they would cause much voltage drop in a battery in good condition and fully charged to proper capacity. The 0.034 amps whist above LVR would never be a worry , and the 0.084A whilst load is sitting in disconnected mode would take a long time to discharge a good battery IMHO.
More testing with a better battery tomorrow to confirm these results. I think you must have other "ghost currents" causing your battery voltage to drop. Remember, lead acid batteries do lose their charge fairly quickly, unlike AGMs. What do you think@Crusty??

I get your figures but as for a ghost type current, the only occurance of significant discharge is contained within the LVC. As soon as that is disconnected all trace of evaporating power ceases. Ill connect the unit you have and see how that goes in comparison to the other 2 x boards.

 

[Brente1982]

Bad Earth?

 

[Crusty181]

Bad Earth?

Continuous terminal free connection direct from the battery, and in the absence of the LVC, drainage is non existant

 

[Boots in Action]

Continuous terminal free connection direct from the battery, and in the absence of the LVC, drainage is non existant

Don't forget @Crusty181 that the small LEDs showing current battery voltage continuously are going to use some power, more so when the voltage drops below cut out setting and warning light also comes on. But , in doing that, it has performed its job by protecting battery from descending into a dangerously low discharge state which would be the end of your battery. I believe the unit is designed to do just that and if your fridge (or other load) stops working, you are at least aware of a low battery, or as low as you determine. As all small portable compressor fridges have various voltage cutouts, they too would be drawing that same small current. I guess even a small volt meter connected that way would have to use some current if it has any type of LED display. Not much good without a display of some sort, although a push button to turn display on when required would overcome this. I will confirm figures again after further testing with a good AGM battery, but will change the settings for both LVD and LVR to 12.40v and 12.80 volts respectively, so as not to push AGM to lower voltage unnecessarily. And who leaves a load on a battery for a week or more and does not keep a check on battery voltage unless connected to constant power supply? I wouldn't.

 

[Crusty181]

Don't forget @Crusty181 that the small LEDs showing current battery voltage continuously are going to use some power, more so when the voltage drops below cut out setting and warning light also comes on. But , in doing that, it has performed its job by protecting battery from descending into a dangerously low discharge state which would be the end of your battery. I believe the unit is designed to do just that and if your fridge (or other load) stops working, you are at least aware of a low battery, or as low as you determine. As all small portable compressor fridges have various voltage cutouts, they too would be drawing that same small current. I guess even a small volt meter connected that way would have to use some current if it has any type of LED display. Not much good without a display of some sort, although a push button to turn display on when required would overcome this. I will confirm figures again after further testing with a good AGM battery, but will change the settings for both LVD and LVR to 12.40v and 12.80 volts respectively, so as not to push AGM to lower voltage unnecessarily. And who leaves a load on a battery for a week or more and does not keep a check on battery voltage unless connected to constant power supply? I wouldn't.

Boots my Engel is pre LVC which is a good thing because I think the adj variety LVC provides a far better outcome when I can fine tune the LVC to suit my hardware.

Buggering around with relatively normal SOC ad higher LVCs parameters I noticed with the with just the fridge running once the LVC kicked in and did its job the voltage then spiked significantly. Now I know the LVC itself drains the battery, that battery voltage spike/rebalancing with no load would likely cover off any of the negligible short term LVC circuitry drain until the point that I noticed the fridge was off. ie it wouldn't compound an already flattened battery by making it worse. I suspect in the short term with only a LVC lights it probably wouldn't actually get back down to that LVC setting ... if thats makes sense

When buggering around with the LVC to set the field use parameters I had the LVC set quite low because I want to find that sweet spot where I can identify the point where its the most battery energy able to be used, but retain a small margin to still start the car. I had the fridge, headlights and heater fan sucking the guts out of the battery to find that point, I had the solar on standby in case I went a little too far.

The only reason I noticed any of this battery drainage is because of the bluetooth battery monitor, and it was constantly alarming with nothing on accept the LVC. How accurate my battery monitor is who knows, but its better than nothing and it found this so thats a decent win for it right there. The battery monitor also keeps a record of crank voltage drop which is really handy because that will give me a good indication over time of any consistent deterioration in battery health. It continuously records a voltage graph which you can watch in real time (not quite as entertaining as Netflix), or at least see a slow or fast drain on the battery over time. And then there are my favs, the voltage alarms which I have set at 80% and 60%. Once the voltage drops to 80% it continuously (and I mean annoyingly continuously) pings the phone.

In practical camping use I will generally rely on the battery monitor alarms, and the LVC will only be an "when all else fails", or I cant afford to allow the fridge to turn off ie its full of fish. (yeah yeah, probably never. Disney movies taught me if you believe, youll achieve)

The car has been sitting idle now for two full days and the battery monitor has the battery down to 95%. With the LVC on, by this stage or certainly tomorrow the 80% alarm would be pinging me.

I suppose in a fair review, using the LVC in an practical environment it does its job quite well. Its providing infinitely adjustable parameters to get maximum value. It provides a visual indication located next to the fridge of just how much run time the fridge has left without some external power input. It provides me with the all important peace of mind that Ill be able to start the car, or at the very least make conscious and deliberate decision to bypass it. The down side or LVC negatives relates only to the time Im not actually relying on the LVC functions, and for that I can just pull its fuse or use plugs instead of hard wiring it.

 

[mikerezny]

Hi @Crusty181,

if you have a bluetooth battery monitor across the battery all the time, it will also be drawing some current.

It doesn't take much current running 24/7 to become significant.

I have been in this field for almost 60 years. So, a lot of the things I do are second nature and I never consciously think about them.
One is that I know the power / current draw of every single 12V device in the van.
Measured them once and wrote them all down in my little black book.

At home, I know the standby power usage of every appliance and switch everything off that is not making a contribution to our requirements.

I bought a 240V power analyser from Aldi for $20 many years ago. On the first run around measuring things, I found a Yamaha three-in-on next to the TV which we had not used for many years. It was plugged in and its standby power draw was over 10W. That is 90kWh per year. At 20c per kWh that is $18.
So the meter paid for itself on just that appliance.
From memory, I think I found about 100W of useless items wasting power.

take care
Mike

 

[Crusty181]

Hi @Crusty181,

if you have a bluetooth battery monitor across the battery all the time, it will also be drawing some current.

It doesn't take much current running 24/7 to become significant.

I have been in this field for almost 60 years. So, a lot of the things I do are second nature and I never consciously think about them.
One is that I know the power / current draw of every single 12V device in the van.
Measured them once and wrote them all down in my little black book.

At home, I know the standby power usage of every appliance and switch everything off that is not making a contribution to our requirements.

I bought a 240V power analyser from Aldi for $20 many years ago. On the first run around measuring things, I found a Yamaha three-in-on next to the TV which we had not used for many years. It was plugged in and its standby power draw was over 10W. That is 90kWh per year. At 20c per kWh that is $18.
So the meter paid for itself on just that appliance.
From memory, I think I found about 100W of useless items wasting power.

take care
Mike

Now that you have planted that seed, its very easy to over look many things particularly those out of sight out of mind items that don't make an obvious and theatrical impact. A good example would be the diesel heater. The display and thermometer are always on, but I wouldnt ordinarily consider to be drawing any power unless heat was pumping out the duct. As for the cars battery monitor itself, never considered that either but again until the LVC appeared there was no significant loss of power, the monitor alarm never warned me about itself as amusing as that would be; sort of "help help, Im killing myself". It will interesting to see how the unit Boots has fares against the boards I have, although Im guessing same function probably same outcome.

I also had one of those Aldi meters, and it was really handy particularly when I was testing the aircon and generator compatibility. Unfortunately the screen on mine lost its mojo a long tine ago, displaying only partial info so in the bin it went. They are still on eBay anyway should I need another. I don't bother with anything from Aldi, the odd things Ive ended up generally failing or under performing. On the rare occasion I inadvertently come across an Aldi item that sparks an interest, Ive just used it as motivation and sourced the goods elsewhere.

 

[poor but proud]

Now that you have planted that seed, its very easy to over look many things particularly those out of sight out of mind items that don't make an obvious and theatrical impact. A good example would be the diesel heater. The display and thermometer are always on, but I wouldnt ordinarily consider to be drawing any power unless heat was pumping out the duct. As for the cars battery monitor itself, never considered that either but again until the LVC appeared there was no significant loss of power, the monitor alarm never warned me about itself as amusing as that would be; sort of "help help, Im killing myself". It will interesting to see how the unit Boots has fares against the boards I have, although Im guessing same function probably same outcome.

I also had one of those Aldi meters, and it was really handy particularly when I was testing the aircon and generator compatibility. Unfortunately the screen on mine lost its mojo a long tine ago, displaying only partial info so in the bin it went. They are still on eBay anyway should I need another. I don't bother with anything from Aldi, the odd things Ive ended up generally failing or under performing. On the rare occasion I inadvertently come across an Aldi item that sparks an interest, Ive just used it as motivation and sourced the goods elsewhere.

While talking about unexplained power usage , when we first got our van it did not have a battery installed the set up only allowed power from 240 or car circuit. When we installed a battery we were still using power when nothing was turned on, after trial and error it was traced to the radio CD player which is a typical car unit which even when turned off stays in standby mode which uses the same power as if turned on. You can turn the unit totally off but any disruption to power feed put the unit back to standby mode we had to install an isolation switch to stop this happening , car radio/CD draw around 8 amp even when on standby this is not an issue in a car as the ignition switch isolated the unit ,by the way some tv units do the same thing , silent sneaky battery killers as if not known totally drains battery and causes battery failure in no time , not sure if this is common or my van was built Friday pm

 

[Crusty181]

While talking about unexplained power usage , when we first got our van it did not have a battery installed the set up only allowed power from 240 or car circuit. When we installed a battery we were still using power when nothing was turned on, after trial and error it was traced to the radio CD player which is a typical car unit which even when turned off stays in standby mode which uses the same power as if turned on. You can turn the unit totally off but any disruption to power feed put the unit back to standby mode we had to install an isolation switch to stop this happening , car radio/CD draw around 8 amp even when on standby this is not an issue in a car as the ignition switch isolated the unit ,by the way some tv units do the same thing , silent sneaky battery killers as if not known totally drains battery and causes battery failure in no time , not sure if this is common or my van was built Friday pm

Ill add in some weird caravan stereo shenanigans. The aircon and tv remote controls turn our caravan stereo on (never off) and also changes the channels. A problem, but not such a massive surprise you'd expect, having one remote impact another. But here's where the weird ramps up to a whole new level, our caravan stereo doesn't (read does NOT) have a remote control itself. You can imagine how many years it took to figure out what the hell was going on

The stereo also has outside speakers and we generally only use it outside so whenever we use the stereo we have to ensure the volume is zero before we turn it off because we learned the hard way lying in bed late at night changing a channel on the tv, or adjusting the aircon turns the bloody stereo on outside at the settings it was turned off at ... we cant have a giggle and then just turn the stereo off with its remote control because it doesn't bloody have one