An unusual 12V (starter) battery question

[ProDave]

Skip this first paragraph if in a hurry, it gives some background. I have 2 batteries in the the truck, set up by previous owner, the 12V starter battery and another lead acid leisure battery to power cab gadgets and a general purpose inverter in the cab. (also a third battery in the habitation unit). These 2 truck batteries are charged from the alternator with a split charging setup. There is also a volt meter in the cab in a not very convenient place, and I noted it is often showing less than 12V, sometimes as low as 11.5V but everything seems to work including starting the vehicle. But yesterday I decided to investigate and found it was the starter battery reading under 12K if left for a while.

So starter battery if left for a while (3 weeks since last starting the truck) was reading about 11.5V but it still started the truck just as normal with no hesitation cranking. So assuming it is a typical modern vehicle that drains power all the rime for things like the alarm, after sitting a while It was nearly flat. So after confirming it started the vehicle okay, I put it on charge with my battery charger and left it on charge all day.

This morning it is already back down to 12.0V I expect another day or 2 it will be under 12V again.

This has me puzzled. It it not normal behaviour. Not normal in the sense that whenever I have had a battery drop in voltage like that, the battery is on it's last legs and really struggles to crank the engine over. But this one although reading low, does not flinch in the slightest at starting and had it not been for that voltmeter in the cab, I would not even be looking at it. I have had this truck for 8 months now and I am sure it has been like this all that time and even in winter starts perfectly.

So how can a battery consistently read a lower voltage than it should, yet seemingly work in every respect and even hold enough charge to start the vehicle after 3 weeks? The conflict is I would expect a battery reading low voltage to struggle starting and not hold charge, but this battery does hold charge and starts fine so why is it reading low?

 

[Bertietoo]

Have you checked the voltage actually at the battery with a real multimeter?
I would suspect the voltmeter in the cab.

Steve

 

[r4dent]

My first thought is that there are a lot of assumptions being made in your statement, especially because the installation was done by a previous owner and is (presumably) undocumented.

So I think the first thing you should do is to personally verify the cab wiring system and produce a wiring diagram.

Start with basics like proving that the "starter" battery is the one that turns the engine over! Just because it is located where the starter battery resides as standard doesn't mean that it is the starter battery.

 

[maingate]

Dodgy voltmeter? Double check the voltages with a meter.

 

[AndiHP]

As already written bevor, get a Voltmeter, and go directly to your battery poles an read out there. I think you will get different values than your onboard meter. than check the wiring from the Battery to the meter and my be the easiest way could be to cut off the old wiring and set a direct new wire through your truck just to see if over this wire the meter gets better values. If yes, than you now the issue is the old wire, or a connection anywhere.

 

[ProDave]

Yes to be clear I have verified that the starter battery is that, the original location and wiring by Toyota, a 75AH lead acid battery. And voltage readings confirmed with my reliable Fluke multimeter. It was the odd reading on the dash volt meter that made me look harder. On further inspection the dash volt meter will show 2 different voltages and they confirm the readings I get from the fluke multimeter on both batteries.

The bit I have not really confirmed is how the second battery is charged there is some kind of split charging device but I have not yet searched the part numbers to determine if it is a relay or diode based split charge setup.

The very presence of a second cab battery is strange, I only know for certain it feeds the inverter in the cab and a whole host of 12V sockets in the cab and the previous owner must have had lots of gadgets plugged in to justify fitting it.

Habitation power is quite separate a 100AH Lithium battery and Victron charging system and 2 big solar panels.

I have yet to get my DC clamp meter on it to see what current is being drawn by the "always on" 12V stuff in the vehicle, from that I should be able to calculate how long it would take to flatten the starter battery when not in use. I will try that later when it stops raining.

It is just so odd that a battery can read too low, yet hold it's charge and still be able to deliver power for cranking even after a long period of no charge, it does not sit with the normal symptoms of a failing battery.

 

[r4dent]

I don't understand

On further inspection the dash volt meter will show 2 different voltages and they confirm the readings I get from the fluke multimeter on both batteries.

How does the dash volt meter show 2 readings?
Do the alternate? Is there a selection switch?

It is just so odd that a battery can read too low, yet hold it's charge and still be able to deliver power for cranking even after a long period of no charge, it does not sit with the normal symptoms of a failing battery.

I'm wondering if the "cab inverter battery" is helping with the starting.

What size cable connects it to the starter battery?

When the starter is showing low volts try disconnecting the inverter battery.

What engine are we talking about?

 

[wildebus]

I used to sell a little "Battery Watch" kit that comprised a wiring kit plus selector switch and voltmeter which you would use to monitor the starter and the leisure batteries with the one display.
Didn't include it when I revamped my website a couple of years ago ... maybe I should add it back in as not seen any similar products on sale anywhere?

 

[trevskoda]

I have 2 volt meters on my dash, right unit close to s wheel is engine starter, left one les bats, switches beside then are on offs.

 

[ProDave]

The dash volt meter has a button to select which battery voltage it is reading.

I have tried with the dc clamp ammeter. They are notoriously fickle things particularly at low current, but it is telling me at rest the vehicle is drawing 0.28 Amps. If that were the case it would flatten a 75AH battery in 267 hours or 11 days. Since it still started after 3 weeks of inactivity the real figure must be lower.

I think what this is showing is for such periods of inactivity it needs some kind of maintenance charger. Kind of ironic I have more than 200W of solar panels on the roof and it would be easy to configure a maintenance charge from the habitation battery (being discussed at the moment on this forum) however as this is a demountable setup, not such an easy thing to physically arrange, as any additional wiring would also need to be disconnectable. I do have a spare 12W solar panel that I could easily connect when parked for a while which may be enough, I had this from the previous trailer caravan to keep the leisure battery topped up.

The engine is Toyota's 4 pot 2.4L turbo diesel.

 

[maingate]

If you have a good solar setup, how come your batteries are draining? Particularly at the height of Summer?

Rip the batteries and wiring out and start again from scratch would be my advice.

 

[ProDave]

If you have a good solar setup, how come your batteries are draining? Particularly at the height of Summer?

Rip the batteries and wiring out and start again from scratch would be my advice.

The solar setup charges the habitation battery only. This is the starter battery.

Because the unit is demountable any additional wiring to organise a maintenance charge to the starter battery from the solar would also need to be disconnectable.

 

[r4dent]

Thanks for he post, a picture can be worth 1,00 word.
When your first post said "There is also a volt meter in the cab " I didn't assume two volt meters.

One thing I noticed

it is telling me at rest the vehicle is drawing 0.28 Amps. If that were the case it would flatten a 75AH battery in 267 hours or 11 days.

A (I assume) lead acid battery only gives half it's nominal capacity before it is flat. (75/2) / 0.28 = about 5 days.


I'm off for lunch I'll give it some more thought this pm.

 

[maingate]

The solar setup charges the habitation battery only. This is the starter battery.

Because the unit is demountable any additional wiring to organise a maintenance charge to the starter battery from the solar would also need to be disconnectable.

If you are using the pickup in normal circumstances, the alternator should keep the engine battery charged. If you do not need the pickup for daily use at home then you could add the engine battery into the solar charging system.

You have stated that you did not use the pickup for 3 weeks, so my suggestion has some merit. The additional wiring to include the engine battery can be as long as you want (within reason) and would solve your problem.

 

[ProDave]

Yes I am going to have to start working out the wiring between the pickup and the demountable camper. There are basically 3 connectors, one is a 13 pin trailer socket, I am pretty sure that is just used for the road lights on the back of the camper. There is a 3 pin 16A commando type connector (normally used for mains) that I suspect is used from the split charging system to charge the leisure battery when driving. And then a tiny little one for the reversing camera. I need to draw out a circuit diagram and work out if any of the existing connections can be used to charge the starter battery from the solar panels.

 

[ProDave]

Some pictures, and a beginning of understanding how it works.

the charger.

I don't have the instruction or installation manual, I need to go and find that and download it.

It appears the high current terminals are Battery 1, ground, battery 2 and PV input. All connected.

Battery one connects to the 100A lithium battery right behind it under a seat.

Battery 2 connects to the big connector going to the pickup truck.

Looking under the bonnet, here are the 2 batteries there

The bottom one in the picture is the starting battery and the top one I will call aux battery.

There is this device which I think might be a split charger of some sort but I can't see any model numbers on it

And there is this mounted next to the batteries.

It doesn't appear to have any heavy wires connecting to it so suspect it may be something to do with the dashboard volt meter?

Now some measuring. Both battery outputs from the Victron show voltages of around 13.7V One as states is the lithium battery in the camper, so the other must be one of the truck batteries. Given the starter battery at the time was reading 12.1V it is not that.

So my initial conclusion is the Victron is charging the internal battery in the camper and the aux battery under the bonnet but not the starter battery.

Initial thoughts to help maintain things through a layup between uses, is to connect a maintenance trickle charger (like already being discussed elsewhere) between the aux battery and starter battery. That should do it without any major rework.

If anyone recognises the red and blue boxes in the pictures please let me know.

 

[r4dent]

If anyone recognises the red and blue boxes in the pictures please let me know.

HC Cargo 161059

Amazon.co.uk

 

[trevskoda]

The simple way to get power to piggyback unit would be to use a towbar plug with double ends, so one end into truck other into a socket on mountable unit, takes a irish man to sort things, i was never beaten yet, but when i do i will let you know if i enjoyed it.

 

[r4dent]

If anyone recognises the red and blue boxes in the pictures please let me know.

The company name on the red box would be useful, can't make out the first few letters in the photo.

 

[ProDave]

The Victron manual is here https://www.12voltplanet.co.uk/user/Votronic-VBCS-triple-charger-instructions.pdf

What I thought was a second battery output is the vehicle battery input, shown in the manual as directly connected to the starter battery. But in this case it is not connected to the starter battery but to the aux battery.

The car go box might be the thing that does the split charging from alternator to aux battery then?

The red unit, the "name plate" appears to be cardboard and already in poor condition. I think it says Gordon Equipments Ltd but it is hard to make out even in the flesh so so speak. No sign of a model or type number.