Bluetooth Battery Monitor for iOS and Android

[JohnnyUK]

I've been reading various threads on here about flat batteries on WAV vans/cars, same happened to my little VW Caddy the other day. Weather is bad here in the UK so it's not easy to go outside in the ice to access battery and check charge level.

I've ordered one of these so that I can check battery charge level of van from inside the house ... https://www.aliexpress.com/item/1005004 ... 1802BtbKgu

Maybe you guys already know about such things, I'm new to the WAV scene so forgive my ignorance if that's the case. But if you don't know about these and worry about your battery it's surely worth a look? Hope this is helpful

[Burgerman]

It can help some. But you also need some understanding of what its showing you.

When you say monitor the battery, I am not sure what you think its going to tell you exactly. Unless you understand the following it wont likely help a lot.

A FULL battery or a battery at 99% full, will read around 12.95 to 13.2V. If its not connected to anything.
A battery at 90% full that is not connected to anything will read around 12.8V.

A battery at say 12.4V is either around 50% discharged, if its just sat disconnected, or 80% charged if its been sat in a van that is gradually discharging it.
The AMOUNT that it reads is "artificially" low, depends on many things such as the length of time since charge, previous charge or discharge history (called peukert and takes around 16 hours to recover correct voltage). And so on. So a small drain of even 70mA will cause a battery voltage to read much lower than its actual open circuit voltage and give an incorrect state of charge measurement.

So a battery at say 12.5V can be either nearly full, or less than half charged. Depending on recent history, current drain current, temperature, and peukert level and any slow drain current that it has from the van.

What are you hoping to see?
I suspect that you will see around 12.4 to 12.6V after its been driven, maybe 2 hours later. At that point its still 98% or better charged... But will look as if its not.



In my own van I do what is the only sensible solution.
Since all lead batteries have being discharged, even a little for long periods, I hold it at 13.2V which is the level that holds it 100% full, without any real charge current which would otherwise damage it long term. This is done witha solar panel, and charge controller, and in winter via an extention cable and a wall wart set to 13.2V. In both cases a perfect long term float voltage.

That way I know the battery is always at the perfect 100% charge. And will live at least a decade.
I also have an anderson connector on the dashboard, and under a wheelarch.
So I can connect my chair to it to start it in the event I leave lights on or something, and so that as I drive the van charges the chair.

THIS is only valid if you disconnect he battery competely, wait 16 to 20 hours before measuring.
As if there is a small drain as in your van the voltage will otherwise read way less, than it otherwise would.

[Burgerman]

Worse, the engines starter draws anything from 100 to 500 Amps depending on temperature as you crank it.

This means that in winter a 65% fully charged battery likely cant start your engine. Because the impedance increases as state of drops and temperature.
In summer though a 40% charged battery will probably start it great.

But heres another thing. If you have a fully charged 13.00V battery, and crank the engine for 3 seconds that will make the voltage drop to around 10V instantly, and then it will rise again. Initially it will do so very fast. After 2 or 3 mins it might be 12.5V. After 15 mins it might be 12.75V. Its really still 99% charged. And it will eventually get back to almost 13V again over around 16 hours. During this time the voltage continues to increase, but state of charge remained the same or dropped a little. This is why when you try and start a car it stops cranking. But leave it an hour or so and it fires up.

Unless theres a small residual drain current caused by a fault. In which case it may never recover or get past say, 12.5V... Yet still be almost a fully charged battery.

So state of charge DOESENT = Voltage.

So any gadget that tries to determine the battery state of charge based on its voltage cant really tell you very much unless you disconnect it completely and wait 16 to 20 hours... Lead batteries are terrible things. All this inaccuracy is caused by a thing called the surface charge effect or Peukert after the guy that discovered it.

[LROBBINS]

THIS is only valid if you disconnect he battery competely, wait 16 to 20 hours before measuring.
As if there is a small drain as in your van the voltage will otherwise read way less, than it otherwise would.

If you do this on any recent car you will zero out all of its electronics (the Renault dealer just did this to us a week or so ago, and when they reset it, it came back in French rather than Italian).

There is substantial residual drain in these cars, and not just from a fault - it's built in.

[Burgerman]

And on many modern cars. They all really need a roof solar panel and charge controller. And a low impedance deep cycle capable starter battery like the odyssey.

[JohnnyUK]

@Burgerman - Fair comments I appreciate it won't give me dependable readings, I'm not expecting a Fluke for less than £30. For me the interesting thing about this product is that it measures and analyses much more than voltage for which the claimed accuracy is +/- 0.03V. It also checks Cold Cranking Amperage, internal resistance and gives a warning if the preset low voltage level has been reached. It also has a data logging function that constantly records battery state over 30 days (I think), this would be handy for showing trends with variation in battery use.

I'm sure it'll be far from perfect and I appreciate interpretation of any data is dependant on my understanding of how lead acid batteries work. Unlike yours my WAV is garaged so solar wouldn't be the answer, I'm thinking of fitting a charging port to the van so I can leave it on charge when not expecting to use it for a few days. In the meantime the BT2000 should tell me if the battery charge state is low enough to need a charge before I attempt to start the van, I'll also get a better idea of how quickly battery discharges when van is idle.

@LROBBINS - I didn't realise (until now) that current drain is an endemic problem with WAV's, thanks for pointing it out though

[Burgerman]

@Burgerman - Fair comments I appreciate it won't give me dependable readings, I'm not expecting a Fluke for less than £30. For me the interesting thing about this product is that it measures and analyses much more than voltage for which the claimed accuracy is +/- 0.03V.

You missed the point. My fluke wouldnt tell me the state of charge either. It is nothing to do with its accuracy its because of the way lead batteries work. So it CANNOT know the state of charge, only its voltage. Which is a totally different thing. UNLESS you disconnect the battery, wait 16 hours, then compare to the batt manufacturers state of charge V voltage chart @ the specified temp - normally 25C.

It also checks Cold Cranking Amperage,

It cant.
It estimates that - and uses a default average for the peukert value, based on its inacurate impedance reading. I doubt it can accurately read impedance either for several reasons, including that it would need an in built 1k cycle AC voltage generator and 4 wires.

and gives a warning if the preset low voltage level has been reached.

What voltage will you set?
Because a battery that is sat with a permanant low drain on it will read around 12.4V even if its 80% charged. And a battery that doesent have this, will read 12.8V. So any fixed voltage point will not tell you the state of charge, only its voltage!

It also has a data logging function that constantly records battery state over 30 days (I think), this would be handy for showing trends with variation in battery use.

Maybe... Depends. Better some info rather than non, but you seem to think it behaves like a lipo hobby battery. It doesent.

I'm sure it'll be far from perfect and I appreciate interpretation of any data is dependant on my understanding of how lead acid batteries work. Unlike yours my WAV is garaged so solar wouldn't be the answer, I'm thinking of fitting a charging port to the van so I can leave it on charge when not expecting to use it for a few days.

YES. You want something set to 13.2V. Not more, not less. Thats is what you need to keep the battery topped up and not cooked long term.
I use one of these:
https://www.ebay.co.uk/itm/395664524092
I have one on my van. I have another on each lead chair I have sat unused. Set to 13.2V or 26.4.

In the meantime the BT2000 should tell me if the battery charge state is low enough to need a charge before I attempt to start the van, I'll also get a better idea of how quickly battery discharges when van is idle.

No it wont. And if its anything less than 100% charged, then it is gradually sulfating and dying.

@LROBBINS - I didn't realise (until now) that current drain is an endemic problem with WAV's, thanks for pointing it out though

Not JUST weelchair vans. ALL modern vehicles with remote entry, clocks, a permanantly active memory in the engine management system, radio clocks, alarms and immobilisers.

Unless driven several times a week the battery will soon die and need replacement. Or fail to start. Lead based batteries *must* sit FULLY charged when not in use or suffer a very short lifespan.

[Burgerman]

https://www.wheelchairdriver.com/board/ ... =2&t=12590

Read!

[JohnnyUK]

Thanks for your comments appreciate your time responding. I didn't realise battery drain is a feature of most modern cars rather than just your heavily adapted mobility vehicle. Reading threads on here about battery failures then finding myself in same position has made me paranoid. I do take your point that lead battery tech isn't simple and proper maintenence requires a decent understanding of testing limitations.

I set off with the objective to test battery voltage without going to van and physically checking with a multimeter, it's not easy for various reasons I won't bore you with. I think the BT2000 should at least do that remotely, anything else is a bonus. There's a number of features that may well be dubious but should show comparative trends. I'll take on board your suggestion to establish a system where the battery is maintained as close as possible to 100%. In answer to your question I'd set the voltage alarm to 12.0 volts which I think should indicate that a charge is required NOW

[Burgerman]

I set off with the objective to test battery voltage without going to van and physically checking with a multimeter, it's not easy for various reasons I won't bore you with. I think the BT2000 should at least do that remotely, anything else is a bonus.

You still appear to think that battery voltae represents the battery state of charge!
But the battery voltage is NOT an indicator of state of charge when fitted into a vehicle, It will read lower AT THE VERY SAME state of charge, depending on the severity of your battery drain current. And we already know there is one. So the only thing it will show you is the voltage that will appear to drop way below the point that it NEEDS CHARGING NOW which is anything below 12.7V. Ideally 12.95V. When in fact it may not be very discharged at all in reality.
What it will show you is some official looking voltage numbers that look good, that dont really tell you anything much that is useful or the actual battery state.

If it reads say 12.4V and you then DISCONNECT the battery from the car, its voltage will rise over 20 hours or so to 12.8V or some other figure depending on the load it had. So which is the correct voltage? Did it "recharge" itself??
If its REALLY 12.4V then that battery wouldnt start your car. Because impedance increases as it becomes discharged. All you really read was the surface charge state.

There's a number of features that may well be dubious but should show comparative trends. I'll take on board your suggestion to establish a system where the battery is maintained as close as possible to 100%. In answer to your question I'd set the voltage alarm to 12.0 volts which I think should indicate that a charge is required NOW

No it wont and thats the point!
In any case a sttarter battery reading 12V is permanantly now damaged. They are not meant to be deep cycled.
It could also (very likely) indicate that its been sat a while with a high drain current. But is really still about 70% charged... Or if theres no or little drain current from the van it will tell you its dead and damaged. Which is it? You CANNOT know unless you disconnect it, wait 16 hours or so, and then measure it.

So since anything below 13V is damaging and sulfating the battery, and anything above 13.4V is cooking it and costing elecrolyte and causing grid corrosion, it needs to be held at 13.20V long term like more than a week to forever.

[JohnnyUK]

@Burgerman - ok I accept there's no point measuring voltage of an installed battery, you seem to be saying battery can't be checked in the vehicle so don't even try. I'll get another of those cheap Chinese 2.5A Power Supplies and get a weatherproof socket installed outside van and connected to the battery. Once I get the van in garage I can plug a PS into the new socket and forget about it, hopefully the battery will be 90%+ if I've just returned home after driving. Will the 2.5A PS be sufficient to use as described?

Thanks for taking the time to explain in detail why I'm wasting my time ... you must have been through that a few times before

Cheers John

[Burgerman]

A 0.5A one would be overkill. At float CV of 13.20V charge current will fall to less than 20mA + whatever residual drain current the vans systems addover time. Maybe 70mA.

[JohnnyUK]

Does that mean the 60W 2.5A PS is too much for my van application? Won't the battery take what it wants and draw less current or do I need a different PS?

[Burgerman]

Anything from around 0.5A up to 1000A will work exactly the same.
The battery will draw as much as it needs to maintain the voltage at the 13.20V long term maintanance point.

If its discharged, it may sit at 2A for a while first. But eventually it will drop to almost no current, few mA. Just holds it full against the vans small current.

[JohnnyUK]

Perfect thank you once again