EHU under bonnet - flat battery

[Maarten1]

My van is new to me and I had the first off grid trip away last weekend with no issues. When I got home I plugged the EHU in to charge the leisure battery. The EHU is located under the bonnet so I plugged it in, lowered the bonnet but didn’t close it all the way for fear of damaging the cable, locked the van and charged away for the day. Today I went to the van and the starter battery is flat so thought the cold weather may have killed it. Before I buy another I’m wondering if having the bonnet ajar for a day could have run the battery down? Would this keep the van’s electrics “alive” where they usually shut down after about 10 minutes?

 

[Dellmassive]

The EHU on 99% of vans does not charge the starter.

Leaving the bonnet won't run the battery flat.

Two.options.

Add a small charger for the starter battery for when on EHU.

Or

Add a small reverse charger that will trickle charge the starter from the LB.

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[Maarten1]

Thanks for the fast replies Dellmassive. I really don’t understand electrics too much but would you expect the starter battery to remain healthy while using the EHU to power the leisure side of the van? I would have hoped that the starter battery remained separate from the leisure battery and charger.

 

[Dellmassive]

The starter will run flat over a long weekend when camping as every time you unlock the van, it wakes up and turns on lights etc when you open the doors..... All that is powered from the starter.

Most people don't realize that.

And most EHU chargers just deal with the LB side.

 

[Ads_Essex]

Thanks for the fast replies Dellmassive. I really don’t understand electrics too much but would you expect the starter battery to remain healthy while using the EHU to power the leisure side of the van? I would have hoped that the starter battery remained separate from the leisure battery and charger.

As @Dellmassive says, most conversion EHU setups seem to replenish the leisure battery but fail to address the vehicle starter battery.

If you post up some photos and details of your conversion, we’d be able to advise.

Two options:

Add a small charger for the starter battery for when on EHU.

or

Add a small reverse charger that will trickle charge the starter from the LB.

Further to the suggestions above, plugging in a battery charger with the output lead feeding your top cigarette-lighter socket would feed the vehicle starter battery, which in turn may then activate the DC-DC charger to feed your leisure battery - this is presuming your cigarette socket is connected to the vehicle battery, that you have a DC-DC charger and that it isn’t D+ activated.

 

[Maarten1]

That’s great info, thanks for your help. I will have a good read of Dellmassive’s guides and see what I think the best and easiest way forwards is.

 

[Maarten1]

I went ahead and bought the 7 amp Victron IP65 charger as seen in the @Dellmassive “how I done it” threads,with the plan to use the cigar lighter to charge the starter battery. One thing I wanted to check was that my set up isn’t going to cause any issues.

I currently have the van plugged into an EHU and the charger plugged into the 240v plug in the van which is charging the starter battery. Is it ok to leave the van set up like this until I use it next?

 

[Ayjay]

@Maarten1. An expert will come along soon but all I can say is that I've been doing exactly that for over 4 years now with no issues whatsoever (except that my charger is a Ctek MXS 5.0). I also keep another charger stashed in the van (a Lidl cheapie) and when we're on extended road trips, I plug it in occasionally using the same method to give the starter battery a quick boost if the voltage starts dropping - parked up for a few days and a lot of opening and closing doors etc. tends to take it's toll.

 

[Maarten1]

That’s good to hear that you’re doing the same Ayjay. I haven’t got too much knowledge on the electrical side of things so every bit of help is appreciated.

 

[Howzat]

Further to the suggestions above, plugging in a battery charger with the output lead feeding your top cigarette-lighter socket would feed the vehicle starter battery, which in turn may then activate the DC-DC charger to feed your leisure battery - this is presuming your cigarette socket is connected to the vehicle battery, that you have a DC-DC charger and that it isn’t D+ activated.

I've wondered about that myself. So I stick a 5amp charger on the battery and (if) that kicks up the voltage enough to trigger the 50amp DC-DC will I not be depleting the starter battery until the leisure battery is full?

 

[Dellmassive]

I went ahead and bought the 7 amp Victron IP65 charger as seen in the @Dellmassive “how I done it” threads,with the plan to use the cigar lighter to charge the starter battery. One thing I wanted to check was that my set up isn’t going to cause any issues.

I currently have the van plugged into an EHU and the charger plugged into the 240v plug in the van which is charging the starter battery. Is it ok to leave the van set up like this until I use it next?

That's all fine.

7A max charger is ok via the 12v cigar socket.

 

[Maarten1]

That's all fine.

7A max charger is ok via the 12v cigar socket.

Thanks, I can sleep easy tonight knowing I’m not going to burn it down.

 

[Dellmassive]

I've wondered about that myself. So I stick a 5amp charger on the battery and (if) that kicks up the voltage enough to trigger the 50amp DC-DC will I not be depleting the starter battery until the leisure battery is full?

Yes, sort of.

The starter battery will slowly rise from the 5A charger.

At some point the dc-dc may kick in. But at a lower power level. Not 50A.

That will cause the SB to drop and switch off the dc-dc.

So you will see the charger cycling....

Ultimately both batterys will get a charge.

 

[Dellmassive]

Yes, sort of.

The starter battery will slowly rise from the 5A charger.

At some point the dc-dc may kick in. But at a lower power level. Not 50A.

That will cause the SB to drop and switch off the dc-dc.

So you will see the charger cycling....

Ultimately both batterys will get a charge.

More info here..

[Guide] DC-DC Charger (for leisure battery) -- How I Done It --

@Farnorthsurfer did you set the Dc-dc to lithium mode for the TN100 battery? Also have you got any more BM2 views showing more days? Yes the unit is set to Lithium profile. Easy enough to do when it was powered up. Yesterday was a flat line all day as it just sat on the drive. Back to work...

www.t6forum.com

.

 

[Captain Quick]

I went ahead and bought the 7 amp Victron IP65 charger as seen in the @Dellmassive “how I done it” threads,with the plan to use the cigar lighter to charge the starter battery. One thing I wanted to check was that my set up isn’t going to cause any issues.

I currently have the van plugged into an EHU and the charger plugged into the 240v plug in the van which is charging the starter battery. Is it ok to leave the van set up like this until I use it next?

Before connecting a battery conditioner to one of the cab 12V sockets to charge the starter battery, it’s a good idea to first determine whether they’re fed from the starter battery or the leisure battery. In a T6.1 with a factory-fitted leisure battery, both the cab sockets are fed from the leisure battery so if you connect a charger to one of these you won’t actually charge the starter battery.

 

[Maarten1]

Before connecting a battery conditioner to one of the cab 12V sockets to charge the starter battery, it’s a good idea to first determine whether they’re fed from the starter battery or the leisure battery. In a T6.1 with a factory-fitted leisure battery, both the cab sockets are fed from the leisure battery so if you connect a charger to one of these you won’t actually charge the starter battery.

The other bit of advice I got from the files was to buy the BM2’s which showed that I was charging the starter battery. Good job really otherwise I would have had loads more questions.

 

[Howzat]

Yes, sort of.

The starter battery will slowly rise from the 5A charger.

At some point the dc-dc may kick in. But at a lower power level. Not 50A.

That will cause the SB to drop and switch off the dc-dc.

So you will see the charger cycling....

Ultimately both batterys will get a charge.

So the DC monitors the SB volts and see's 14.5 or whatever when the SB is being charged via the mains and kicks in.
Are you saying when the DC fires up there will be volatge drop on the SB so the DC will then power off, then on again when the SB is back at 14.5v and off and on and so on.....?
Won't that happen quite quickly, like maybe a few times per minute?
Any idea what trickery stops the DC pulling the full 50amps from the SB?
I thought the DC just see's 14.5v so kicks in at it's full amp rating.

So many questions!

My simple thinking thought with our alt providing say 180amp then 180 goes into the battery but the DC then uses 50 so effectively the SB is charging at 110amp which is fine
BUT
with a mains charger if only 5amp is going to the SB and the DC is taking 50 then in theory you're pulling 45amps out of the SB taking it down to dangerous/damaging levels until the LB is full and the DC powers off.

I'm mulling this over from a slightly different perspective in my setup by using solar (100w/8amp) in the summer plugged into 12v socket instead of a mains charger.

 

[Dellmassive]

So the DC monitors the SB volts and see's 14.5 or whatever when the SB is being charged via the mains and kicks in.
Are you saying when the DC fires up there will be volatge drop on the SB so the DC will then power off, then on again when the SB is back at 14.5v and off and on and so on.....?

- yes that is what happens.


.

Any idea what trickery stops the DC pulling the full 50amps from the SB?
I thought the DC just see's 14.5v so kicks in at it's full amp rating.

- the 50A charge rate depends on the voltage difference between the SB and the LB, a small 5A charger won't get the starter to 14.2v,.... It will be a very gradual rise in voltage..

So that will slow the cycling down.


In my testing I needed to ramp up the charge current to about 15A @ 14.7v to be able to start the dc-dc to kick in and stay on.


You need high side of 14v to be able to deliver the 50A, but what happens is you get volt drop on the starter battery, which the dc-dc will detect and throttle back untill the voltage stabilizes.... Net effect is the dc-dc will run at a slower amount rate.

But when the engine is running the 150A alternator has enough power to over come the SB volt drop and will allow the dc-dc to pull full power.

 

[Howzat]

That'll do for me. So the DC is smarter when drawing from the SB. Not bam, 50 amps, like I thought. I guess it ramps up and down and wont fully ramp up when it see's the voltage drop on the SB and gradually ramps down to compensate which would stop the on/off scenario I feared.
Ta very much.

 

[Dellmassive]

Yes, it still can cycle but a lot less.

And defo not the the full 50A,... But the rate all depends on the individual charger profile and setup by the manufacturer...but all the ones I've tested worked very similar.

Charge plot from the post above...