Split charge relay question,which battery

[Shedendman]

Just a quick ask whos/whats right here
This is my setup as it stands,its twin battery as below

Both batteries are exactly the same
What i'm asking is this
Which battery terminal should i come off from to feed the "in" on the SCR?
Now i've had one oily rag(mechanic) tells me best from batt1,(which i had in mind in the 1st place),another tells me batt2,(which i'd rather prefer,for ease of wiring to a leisure battery) this being the + of course,and an on looker(who knows everything) at the time saying run a cable from both,hummmmmmmm,not sure about that?????
So what one better place to ask is here
The vans Alt is 96amps,if that helps,unsure what leisure size battery to get yet,its for a 2kw heater and the operation for a chair lift at the back,thats it nothing else
While i'm here,the SCR i'm getting is a 12v 140Amps,is this man enough?
I'm aware about fitting fuses etc
Cheers chaps

 

[Dave-sparks]

How far apart are the two batteries?

You want to keep the charging cables as short as possible to limit volt drop, using the biggest reasonable size of cable helps too.

 

[m_c]

"In" to the split charge relay should be the vehicle battery, as that's the terminal that detects that the alternator is charging.

My main concern would be if it's a newer vehicle, a basic spilt charge relay won't give optimum charging

 

[voipio]

Don't overthink it. Also, don't overload the alternator. A longer path from alternator to the leisure battery e.g. from battery 2, is no bad thing.

A 2kW heater load is asking a lot from a battery, except for something like a kettle, which uses 2kW for a few minutes at a time. A 12V 100Ah leisure battery stores 1.2kWh of energy, of which around half should be considered usable, for decent batttery life, so 600Wh.

As m_c suggested, this is not optimal. Something like a 12V to 12V (DC to DC) charger would give a better charging profile. See the description in this link, for example:

DC-DC Battery To Battery Chargers | 12 Volt Planet

DC to DC chargers, also known as battery to battery chargers. For charging leisure batteries in Euro 5 and 6 vehicles with smart alternators

www.12voltplanet.co.uk

 

[Shedendman]

How far apart are the two batteries?

About 1100mm apart,width of the engine bay

"In" to the split charge relay should be the vehicle battery, as that's the terminal that detects that the alternator is charging.

My main concern would be if it's a newer vehicle, a basic spilt charge relay won't give optimum charging

So your saying Batt1 then,the vans a 1999 Mk5 transit

 

[Shedendman]

Don't overthink it. Also, don't overload the alternator. A longer path from alternator to the leisure battery e.g. from battery 2, is no bad thing.

A 2kW heater load is asking a lot from a battery, except for something like a kettle, which uses 2kW for a few minutes at a time. A 12V 100Ah leisure battery stores 1.2kWh of energy, of which around half should be considered usable, for decent batttery life, so 600Wh.

As m_c suggested, this is not optimal. Something like a 12V to 12V (DC to DC) charger would give a better charging profile. See the description in this link, for example:

DC-DC Battery To Battery Chargers | 12 Volt Planet

DC to DC chargers, also known as battery to battery chargers. For charging leisure batteries in Euro 5 and 6 vehicles with smart alternators

www.12voltplanet.co.uk

The heaters basically for heating up the cab area in the mornings ie defrosting etc 10-20 mins max
Glad i was sitting down when i saw those dc-dc prices

 

[m_c]

On one of those, the bigger issue is likely to be rubbish charging in general due to age and corrosion.

A DCDC charger would help, but provided the van's charging system is in good condition, and you're actually getting over 14V at the vehicle battery, a split charge relay should work fairly well.