T5 - VSR Split Charge with Battery Monitor - Negative cable and shunt?

[Diver_]

Hi all,

In short I have a dual sensing VSR wired up from starter battery to leisure battery.

I also have one of those AiLi battery monitors which uses a shunt wired up in series on the ground side. The monitor seems to work fine with my loads on (just a fridge, some lights, usbs) showing a draw on the leisure battery.

When I switch the engine on, the VSR engages as described, but the monitor doesn't show a charge coming in. It occurred to me I probably have it wired wrong. The monitor will only see what goes through it...obviously, right?

I wired my VSR in before I decided to buy the monitor. So the connection between the two batteries is the usual way for T5s with a +ve cable under the floor, and an earth strap from leisure battery negative terminal to chassis. But then I added the monitor in series from the leisure negative terminal to my loads without thinking much about it.

Surely, this means the monitor has no way of "seeing" the charge from the alternator?




A closer look at the instructions for the monitor shows C- (charge) on the P- end of the shunt also. Is this what I have neglected, that my VSR circuit negative should also be routed through the P- pole of the shunt so the monitor can "see" the charge?







Anyone able to help me here? I think I've realised my mistake, but I don't want or need the monitor to show me anything other than charge to and from leisure battery, If I send a cable from the P- pole to the chassis, to complete the VSR circuit through the shunt, am I at risk of causing any other problems?

Many thanks again for helping a fool out,

 

[Loz]

You are correct in your diagnosis
battery, shunt, chassis
all load negative to chassis
so simply move the chassis strap off the battery and put it on the load side of the shunt.

 

[Dellmassive]

What he said.... =)

Post your results and a few pics . . . . .

 

[Diver_]

Thanks both for the help and confirming my suspicions. Got around to rewiring today, some pics below for anyone interested.

I am now seeing the alternator charge on the monitor, around 10 amps in to the leisure battery when the engine is running.


Excuse the messy wiring. Negative from chassis comes up behind handbrake and in to P- on shunt, along with negative bus bar from fuse holder. Then all negatives from B- end of the shunt to battery.

10 amps coming in.. I'm not sure what this means about the state of my leisure battery really. AGMs are new to me.


Question: the VSR takes a long time to click off, is this okay? It seems the leisure battery is taking a while to drop back down to resting voltage. Aka its staying higher than the cutoff voltage of 12.8 so the VSR stays on for a good hour.

I think the leisure is even staying at a higher voltage than the starter since there is a 2amp drain with the engine off and VSR still engaged! To my mind the leisure is sitting at a higher voltage than the starter after the engine is switched off, causing a flow to the starter.

I recall reading on the T4 forums about a guy with a similar issue (brand new AGM, light loads).

 

[Dellmassive]

it looks like the VSR cutout voltage is 12.65v

so it will stay connected after engine shut off untill the starter battery drops down the the cut off - 12.65v +5sec.




AGM batteries sit at a much higher rest voltage than SLA. which is why its not good to mix them in a system.

the AGM will always be higher than then SLA starter battery.

to get around that issues, you can swap the VSR for a DC-DC charger,

or

upgrade the SLA starter battery to an AGM also.

 

[Dellmassive]

can you post a few more pics of the positive battery connection and the VSR,

just checking the fusing and cabling is correct...

 

[Diver_]

Cheers Dell. Afraid I put the seats back in earlier so pics are hard to get.

I bought this split charge kit to make my life a bit easier. Its 16mm2 110amp cable between the two batteries, fused at either end with a Midi fuse close to each battery.

They actually sent me 125amp fuses, which to me didn't square with the 110amp cable? I stuck 80 amp fuses in instead.

Engine bay - > Fuse -> VSR 'sensing' terminal with red dot. Other VSR terminal -> Fuse - > Leisure Battery. All with 16mm2 cable.

Cheers

 

[funkbus]

Did you connect your starting battery to the Shunt? Or just pick it up via the chassis ground off your Aux battery? Thanks!!

 

[Diver_]

Did you connect your starting battery to the Shunt? Or just pick it up via the chassis ground off your Aux battery? Thanks!!

Just picked it up via the chassis, didn't run anything back to the starter ground.

My VSR set up is very simple but I'm not running anything power hungry so it works great (just a Fridge, some USB charging, and fairy light style lighting).

 

[funkbus]

Nice! Thanks so much for update.

Follow up question... Did you program the battery monitor for overall amp hours from both batteries or just your aux?

 

[Diver_]

Nice! Thanks so much for update.

Follow up question... Did you program the battery monitor for overall amp hours from both batteries or just your aux?

No worries! I did just the leisure (110 AH) as my loads are only ever running off the leisure battery when the engine is off (VSR disconnected).

 

[funkbus]

Thanks for the info! I'll have to see how my system pans out. I've got 100w Solar into aux battery - not sure if the VSR will open both ways. ... Fun adventures. Thanks for the assistance!!!

 

[VW camper]

VSR RUNS only one way to wards leasure... I believe a DC to dc does both ways.
But you can run a buy pass on cable to bumb start if stuck in a hole..

 

[Pete C]

A standard DC-DC charger works one way - it charges the leisure battery.
Some have an option to trickle charge the starter battery from the leisure circuit using solar.

Pete

 

[Loz]

VSR RUNS only one way to wards leasure... I believe a DC to dc does both ways.
But you can run a buy pass on cable to bumb start if stuck in a hole..

No, completely opposite.

 

[VW camper]

VSR RUNS only one way to wards leasure... I believe a DC to dc does both ways.
But you can run a buy pass on cable to bumb start if stuck in a hole..

Thanks all for clarification on this its been recking my head.
Does this mean that my AGM battery is been used to start my van when main battery is too low ? if so can stop the return current? I'll be using a VSR.
Sorry for confusion..
I want to isolate my mains from my leasure battery when parked up , I don't want a isolation switch but want for it to do automatically? how is this possible with my current VSR ?

 

[Loz]

Does this mean that my AGM battery is been used to start my van when main battery is too low ? if so can stop the return current?

no, as a VSR (Voltage switched Relay) only closes when the voltage rises during charging.
But if you use a VSR your leisure battery will only get to 80%.
If you want a full charge you need a DC-DC charger

 

[oldiebut goodie]

Have T5's got smart alternators though? I thought they didn't have them, I don't know- just an impression in my mind ( I went from a T3 to a T6 and missed out the intervening models)

 

[VW camper]

Have T5's got smart alternators though? I thought they didn't have them, I don't know- just an impression in my mind ( I went from a T3 to a T6 and missed out the intervening model

The earlier models not have but the late models do. Personally mine is a 2014 which is not a smart one.

 

[Loz]

Sorry I dropped in to correct some inaccuracies I read and forgot this was a T5 discussion.