Start battery charging mystery

[Jake W]

I'm going round in circles trying to understand what is happening with the starter battery charging system on my 22 plate T6.1 camper conversion.
I have had what I thought was drain problems from purchasing the van and had the battery replaced 18 months ago.
But the continued occasional starting problems with low battery warnings prompted more investigation and has made me think this is not a drain problem but a charging issue.
Having fitted battery monitors on both start and leisure battery I have today found the following.
Having charged the start battery using a NOCO Genius 2, connected between chassis and battery positive I disconnected the charger and battery voltage remained stable at around 13 volts for two days. Having checked drain before charging to confirm 20-30 mA the very slow drop in voltage over two days confirming no undetected parasitic drain.
Now the interesting bit today before unlocking the van I confirmed start battery voltage at 12.9 showing 99% charge on monitor, leisure battery 12.3 53%.
Started and drove the vehicle for 15 to 20 minutes while monitoring voltage. The voltage varied from 12.2 volts lower than before start only occasionally when coasting or with little or no engine load the voltage increased to 13 plus upto 14.9volts. Parked with engine running at the end of the trip voltage says at 12.2 volts.
Locked the van up and let it settle for 30 minutes before checking battery voltages. Start 12.67 and leisure 12.9, so leisure has charged, but start hasen't recovered from cranking.
I know this is probably not long enough to recharge the start, but I'm concerned that the charging system appears to regulate very low below both start and leisure battery voltage for most of the drive time, even parked engine revs have no impact on voltage it remains at 12.2 volts.
Can any one enlighten me is this normal or do I have a charging issue.
I will be tacking a longer trip over the coming days so hopefully will have a clearer picture then.
The question at this point for me is can anyone tell me, does this look like normal battery management system activity?

 

[Salty Spuds]

Starter sitting at 12.2V is normal. Do a search and familiarise yourself with the Smart Charging System. Assuming you have some sort of B2B charger for your LB, then the LB will always sit higher than your SB.

 

[Jake W]

Thanks , I'll do some more research and hopefully the longer run will shed more light on the low battery warnings.

 

[CAB]

If its sat for a couple of weeks the starter will drain.

BM2 battery monitor

Amazon.co.uk

Thread 'Battery Monitoring -- How I Done It --'

22 Oct 2019

Battery Monitoring -- How I Done It --

Part #1

Battery monitoring is a very important part of your 12v system . . . . whether its just the vans starter battery or your leisure setup keeping an eye on the power in your battery bank will keep you from breaking down and make sure your weekends are not cut short from lack of power.

Battery monitoring is even more important with Lithium Lifepo4 batteries as the voltage stays fairly constant for 90% of the capacity.

first off lets look at a few basic 12v meters.

here a great little unit that I've been using for ages....

you can plug it...

• Dellmassive
• battery sensor dellmassive how to guide
• Replies: 333
• Forum: Electrics, Lighting, ICE, Security

• 

 

[Jake W]

That great and yes this is the type of monitoring equipment I'm using.

The question is this monitoring shows that on my van the battery management system is only ever going to a voltage high enough to charge the start battery when the drive system is not under load. For example on start up the voltage drops during start ( normal activity) and then rises to 12.2 volts during driving only ever increasing to a charge voltage above 13 volts when the vehicle is not under load i.e. foot off the gas traveling down hill or coasting. At all other times the voltage remains at 12.2 volts irrespective of rpm even when stationary and out of great.
I find it unlikely that this is normal, in theory I could drive all day and never charge the battery.

 

[Jake W]

This is a trace from a short 15 minute run round the block shows the battery voltage spent most of the run below 12.6 volts only briefly peaking to 13 to 14 volts on the down hill sections.
Hopefully a longer run tomorrow will give more details on the charging behaviour.

 

[Salty Spuds]

This View attachment 296145is a trace from a short 15 minute run round the block shows the battery voltage spent most of the run below 12.6 volts only briefly peaking to 13 to 14 volts on the down hill sections.
Hopefully a longer run tomorrow will give more details on the charging behaviour.

That’s typical smart charge behaviour. Have you had chance to read up on how it works?

 

[Jake W]

The only smart charge info I've been able to find relates to electric car chargers. Is the behaviour the same as the charging system in my van. Can you suggest any links to relevant info.

 

[Salty Spuds]

The only smart charge info I've been able to find relates to electric car chargers. Is the behaviour the same as the charging system in my van. Can you suggest any links to relevant info.

Use the search function, try “Smart Alternator” plenty there to keep you going.

 

[Pauly]

That great and yes this is the type of monitoring equipment I'm using.

The question is this monitoring shows that on my van the battery management system is only ever going to a voltage high enough to charge the start battery when the drive system is not under load. For example on start up the voltage drops during start ( normal activity) and then rises to 12.2 volts during driving only ever increasing to a charge voltage above 13 volts when the vehicle is not under load i.e. foot off the gas traveling down hill or coasting. At all other times the voltage remains at 12.2 volts irrespective of rpm even when stationary and out of great.
I find it unlikely that this is normal, in theory I could drive all day and never charge the battery.

You need to adjust your thinking, your looking at it in terms of fixed voltages but modern stuff has smart alternators so the alternator will only output/raise voltage when required.
If the starter battery is full (its technically over full because you charged it) then the alternator will sit low, if you turn on lots of electrics like headlights and AC/heaters etc then the alternator should kick in and start to increase

 

[ginkster]

It’s how the smart alternator works as part of the Euro 5 and 6 emissions regs. The ECU will aim to keep the starter battery at about 80% (12.5-6ish V) and only engage the alternator when required to charge back up to 80%, or while decelerating/braking. The 80% target is to give headroom to take the charge while decelerating/braking - termed regenerative braking. By charging to 100% you have filled the headroom so the ECU won’t engage the alternator until it gets back to 80%. It will still do some regenerative braking once there is sufficient headroom. You will also see the alternator engage during a DPF regen.

When the alternator is fully idling you will just see battery voltage, when it is just doing top up charge you will see about 13.3v, during regenerative braking or when a greater charge is needed or a adOF regen you will see 14.8-9v.

It’s fairly normal for a healthy battery to drop to 12v ish after 2-3 weeks standing idle depending on what you have on your van that may be draining it (alarms, trackers, USB sockets etc).

If you are wanting to leave the van stood for long periods something like the Ablemail AMT12-2 is a great solution. It will use you leisure battery to keep the starter battery at about 12.3v. If you have solar it will do this forever.

 

[Jake W]

Thank everyone this all answers many questions and confirms my suspicion that short trips and long periods parked up will inevitably result in a battery too low to start the van.
I will look into using a solar panel to maintain the battery when parked up for longer than a week.
Being a bit of a dinosaur whilst I can see the argument and reasons for all the tech stuff I'm not convinced it's always progress.
The smart alternator search proved all the info needed.
Thanks all for great help and advice.

 

[StratosFearXX]

Flippin' complicated isn't it, I'm learning about all this at the moment as well. Very simple setup in my bus but camping (with electric doors) for a few nights this weekend.

 

[ginkster]

Flippin' complicated isn't it, I'm learning about all this at the moment as well. Very simple setup in my bus but camping (with electric doors) for a few nights this weekend.

Maybe too late for this weekend but I’d recommend an Ablemail AMT12-2 to ensure your starter battery isn’t flattened by the doors and other loads while camping. It will take a little power from the leisure battery to keep the starter alive but that’s better than a flat battery.

 

[StratosFearXX]

Maybe too late for this weekend but I’d recommend an Ablemail AMT12-2 to ensure your starter battery isn’t flattened by the doors and other loads while camping. It will take a little power from the leisure battery to keep the starter alive but that’s better than a flat battery.

Thank you, yes might go that route yet, I have a jump starter pack on the way so I won't get stuck, also a BM6 battery monitor thingy so I can see what's going on.

 

[Jake W]

Flippin' complicated isn't it, I'm learning about all this at the moment as well. Very simple setup in my bus but camping (with electric doors) for a few nights this weekend.

Yes it can be a bit frustrating when your looking for a simple camping experience.
My experience is that the electrics wake up after you open or close doors, does some checks then settles down. Each time you open / close a door lock/ unlock the van a load of several amps max 4-5 is drawn from the battery for a few seconds, after anything upto half an hour the battery drain drops back to normal @ 20 - 30 mA.
I now keep unlocking and door activities to a minimum if I'm away for a few days.
My long run last weekend proved the advice correct after a 5 hour drive all batteries we're fully charged and the start was still at 80% plus after 2 days normal opening locking ect. on site. I maintain the leisure battery using a portable solar panel that keeps up with the fridge for a few days.
Good luck with the weekend I'm sure you will be fine.

 

[ginkster]

Thank you, yes might go that route yet, I have a jump starter pack on the way so I won't get stuck, also a BM6 battery monitor thingy so I can see what's going on.

The pack will hopefully stop you getting stuck but won’t stop the starter battery getting flattened and potentially damaged. Even if you are monitoring with BM2 do you have a way to charge the starter battery without sitting idling on the campsite (not very neighbourly!)?

 

[Salty Spuds]

Flippin' complicated isn't it, I'm learning about all this at the moment as well. Very simple setup in my bus but camping (with electric doors) for a few nights this weekend.

Don’t forget that we aren’t using these vans for their intended purpose. They are essentially work vans, expected to be on the road engine running maybe delivering goods or on site. They aren’t designed to be sat for days doing nothing whilst people live in them using power. If we are going to modify the usage, we have to make allowances for that.

 

[StratosFearXX]

The pack will hopefully stop you getting stuck but won’t stop the starter battery getting flattened and potentially damaged. Even if you are monitoring with BM2 do you have a way to charge the starter battery without sitting idling on the campsite (not very neighbourly!)?

Yeah 'stuck' is the only real concern. I'll be on a military airfield with about 20 other people, not a campsite so even if I did have to leave it idling it would be fine.

I could rejig my solar if necessary (which wouldn't work if it was pissing down of course) but then I'd be using the jump pack and getting out of there!

 

[Drive Wayne]

Yeah 'stuck' is the only real concern. I'll be on a military airfield with about 20 other people, not a campsite so even if I did have to leave it idling it would be fine.

I could rejig my solar if necessary (which wouldn't work if it was pissing down of course) but then I'd be using the jump pack and getting out of there!

Definitely a case or two for Captain Ablemail! No more Starter Battery anxiety, very easy to install.