How-To install DC-DC charger to replace VW Split Charge relay

[jcshnz]

I've researched this and it appears vw specify dual purpose batteries and they are ok for starting.

Had another few thoughts about this issue, hmmm, Looking at the pics of the isolating relay earlier in this thread, perhaps all that needs to be done is energise the small red wire, which (perhaps) acts a the relay trigger and will make the circuit in the relay and allow current to flow between the battery banks and thus equalise them.. No? (electricians please consider ... )

 

[larrylamb]

Had another few thoughts about this issue, hmmm, Looking at the pics of the isolating relay earlier in this thread, perhaps all that needs to be done is energise the small red wire, which (perhaps) acts a the relay trigger and will make the circuit in the relay and allow current to flow between the battery banks and thus equalise them.. No? (electricians please consider ... )

It might be helpful to forum members if you updated your details on your avatar so people can see what setup you are running, it currently states T5 on order.

 

[jcshnz]

It might be helpful to forum members if you updated your details on your avatar so people can see what setup you are running, it currently states T5 on order.

Haha, thanks for reminding me, its arrived

 

[Loz]

Had another few thoughts about this issue, hmmm, Looking at the pics of the isolating relay earlier in this thread, perhaps all that needs to be done is energise the small red wire, which (perhaps) acts a the relay trigger and will make the circuit in the relay and allow current to flow between the battery banks and thus equalise them.. No? (electricians please consider ... )

Yes you could do this, however, if the cranking battery is very flat, the current inrush would probably blow the 80amp fuse.

 

[Loz]

Err did anyone point out that leisure batteries are different from starter batteries and not suitable for engine cranking?

True, However all 3 of mine (MY17) are the same AGM Battery.

 

[DrJuanKerr]

Which travelvolts charger does the initial thread relate to? https://www.travelvolts.net/shop
I see nothing resembling the image in the OG post.

Also, I wonder, notwithstanding cost, which would be the "best" solution: This DC-DC methodology or to fit solar panels? Are they mutually exclusive?
Thanks

 

[Loz]

Which travelvolts charger does the initial thread relate to? https://www.travelvolts.net/shop
I see nothing resembling the image in the OG post.

Also, I wonder, notwithstanding cost, which would be the "best" solution: This DC-DC methodology or to fit solar panels? Are they mutually exclusive?
Thanks

https://www.travelvolts.net/product-page/cali-upgrade-kit

 

[jcshnz]

True, However all 3 of mine (MY17) are the same AGM Battery.
View attachment 39967 View attachment 39968 View attachment 39969

A circumstance supported in reporting by my local Dealer who assures me all 3 should be the same type (dual-purpose deep-cycle/starter type)

 

[jcshnz]

Yes you could do this, however, if the cranking battery is very flat, the current inrush would probably blow the 80amp fuse.

Is there some way to build a circuit that senses the voltage difference between the 2 battery banks and activates the trigger on at a preset level perhaps?

 

[Loz]

Is there some way to build a circuit that senses the voltage difference between the 2 battery banks and activates the trigger on at a preset level perhaps?

For the times you need this a Li-on jump pack would be an easier/cheaper/warranty friendly option.
The CTEK 250SA will allow your charger to also charge the starter battery and prevent he need to join them up in the first place.

 

[Legin]

Which travelvolts charger does the initial thread relate to? https://www.travelvolts.net/shop
I see nothing resembling the image in the OG post.

Also, I wonder, notwithstanding cost, which would be the "best" solution: This DC-DC methodology or to fit solar panels? Are they mutually exclusive?
Thanks

I had the same thought. The original intent of all this was to ensure the stop start functionality doesnt prevent fully charging the leisure batteries.

However the solar panel does this automatically to all intents. So I have spent the cash on two solar panels instead and forget the DC DC stuff.

The reality of issues with the starter battery is pretty remote although there are some defective T6 ones being replaced under warranty my friends t6 has just suffered this.

If things got really really tricky in the desert with no aa or rac then a bit of ingenuity would get the leisure battery connected or swapped over Im sure. Chuck some leads or spanners in if folk are that worried.

 

[jcshnz]

snip..

If things got really really tricky in the desert with no aa or rac then a bit of ingenuity would get the leisure battery connected or swapped over Im sure. Chuck some leads or spanners in if folk are that worried.

Its this eventuality that I'm planning for. I've had battery issues out in the wild before now. On boats as well as cars. It seems to me that the relay's job is to allow the linking of the 2 battery banks. If the small red wire is the trigger to close the relay then a simple switch to energise this wire should accomplish this.
As Loz says above, care should be taken WRT charge level of the battery banks before operating the switch, but a starter battery at 11.5 v seem unable to start the vehicle. A little boost from the other battery bank would help in times like this. I appreciate the points that folks are making re the LiIon power packs but I'd like a more elegant solution. Plus with Murphy's law I'd probably leave the dam thing at home or in another vehicle the day I needed it.
Re the 250SA, I don't really see the point of this device in my T5, as both battery banks are getting charged in both static hookup and alternator running modes. Maybe I've missed something about its cross charging capabilities here, but I think not as the original 'complaint' that started this thread is actually what I want to happen, i.e. when the starter battery is inconveniently low then a cross charge from the house bank is initiated. Mine doesn't do this. Not sure why. But is seems likely it would if I manually energised the relay trigger.

 

[Loz]

I only mentioned the 250 as with the smartpass its a good way to divert solar to the starter battery etc. if you were out in thsticks and running only solar for example.

 

[jcshnz]

Its this eventuality that I'm planning for. I've had battery issues out in the wild before now. On boats as well as cars. It seems to me that the relay's job is to allow the linking of the 2 battery banks. If the small red wire is the trigger to close the relay then a simple switch to energise this wire should accomplish this.
As Loz says above, care should be taken WRT charge level of the battery banks before operating the switch, but a starter battery at 11.5 v seem unable to start the vehicle. A little boost from the other battery bank would help in times like this. I appreciate the points that folks are making re the LiIon power packs but I'd like a more elegant solution. Plus with Murphy's law I'd probably leave the dam thing at home or in another vehicle the day I needed it.
Re the 250SA, I don't really see the point of this device in my T5, as both battery banks are getting charged in both static hookup and alternator running modes. Maybe I've missed something about its cross charging capabilities here, but I think not as the original 'complaint' that started this thread is actually what I want to happen, i.e. when the starter battery is inconveniently low then a cross charge from the house bank is initiated. Mine doesn't do this. Not sure why. But is seems likely it would if I manually energised the relay trigger.

So, if the black wire going to the relay is energised, the relay will engage and the banks will be paralleled. I tried this just now. A 12v feed can be grabbed from the fuse box and bobs your uncle: power can be fed backwards and forwards between the banks.

 

[AlanC]

A circumstance supported in reporting by my local Dealer who assures me all 3 should be the same type (dual-purpose deep-cycle/starter type)

I think the key word in this statement is 'should'. Unless you have physically checked all of the batteries, no one can make that assumption.

Alan

 

[Joker 1299]

The more I read about electrics, the less I understand. Is it just me?

 

[WelshGas]

So, if the black wire going to the relay is energised, the relay will engage and the banks will be paralleled. I tried this just now. A 12v feed can be grabbed from the fuse box and bobs your uncle: power can be fed backwards and forwards between the banks.

You are attempting to put in a fix for a flat Engine Battery. Have you found the reason the Engine Battery went flat twice in 3 days?

 

[jcshnz]

I think the key word in this statement is 'should'. Unless you have physically checked all of the batteries, no one can make that assumption.

Alan

The dealer chappie meant that the specification is for all 3 batteries to be the same.

 

[jcshnz]

You are attempting to put in a fix for a flat Engine Battery. Have you found the reason the Engine Battery went flat twice in 3 days?

Im not trying to find a fix for this. I’m investigating a method to link the 2 banks in an elegant way. And have found it. Clearly the engine battery is U/S and will be changed.

 

[AlanC]

The dealer chappie meant that the specification is for all 3 batteries to be the same.

Later models yes, earlier ones, I m not so sure.

The vehicle specifications certainly do change between years and as technology progresses. However, unless your dealer checked on the VW Germany online computer system, I would still say that 'should' remains the operative word.

My original equipment engine battery replacement from my local VW dealer this year was a Varta wet Lead Acid battery.

Alan

 

[kave]

So, if the black wire going to the relay is energised, the relay will engage and the banks will be paralleled. I tried this just now. A 12v feed can be grabbed from the fuse box and bobs your uncle: power can be fed backwards and forwards between the banks.

I have a fried who is an electrician who works for a power company. This it what they do on their VW Transporters when they need the most power from the batteries and when keeping the engine running to force the alternator to charge both batteries. The have a small switch to engage this mode. I am considering this too and use as a backup solution if my engine battery even gets flat so I can charge both batteries from solar power.

 

[rod_vw]

It's not often that electricians get 'fried'!!

The problem with 'Blue Motion' Transporters is that the smart alternator restricts the engine battery charge to around 80% thus leaving capacity for the regeneration charging. Consequently the leisure battery(s) only get the same limited charge. With a Battery to Battery unit installed the voltage supplied to the leisure battery(s) is sufficient to fully charge then regardless of the limitations created by the smart alternator.

 

[EddieEagle]

The more I read about electrics, the less I understand. Is it just me?

No........

 

[MattBW]

I've been thinking about this again and I can't help but wonder what the downsides of this are. VW must put these 80% caps in for a reason, so what are the negatives of this solution? If your batteries are 100% full and the regenerative braking then puts some power back into the battery, does this cause an overcharge or issue?

Sorry if its already been answered in the thread.

 

[Loz]

I've been thinking about this again and I can't help but wonder what the downsides of this are. VW must put these 80% caps in for a reason, so what are the negatives of this solution? If your batteries are 100% full and the regenerative braking then puts some power back into the battery, does this cause an overcharge or issue?

Sorry if its already been answered in the thread.

it only needs the starter battery for reserve, if that happens to be full it just won't bother doing any regenerative braking.

Think of it the other way round, to reduce load on the engine and therefore improve the overall mpg, it idles the alternator whenever it can, but to complete the charge of the battery it uses regenerative braking, so the starter battery does get to 100% but not if you are charging all 3 batteries. Plus as mentioned at the very start of this thread, with the split charge relay closed, power flows back from the leisure side to the starter side so the ECU still thinks it has 80% or more and they all slowly drain until it decided to charge, but by then all the leisure batteries have been depleted below their optimum for camping use.