Solar wiring question.

[sydnsue]

I am about to change my solar controller from a single battery type to a Truma SDC10 that also charges the vehicle battery. Reconnecting the leisure battery is easy but the new connection to the vehicle battery is not so obvious. The controller has plus and minus output for the vehicle battery. Do I run just one positive wire to the battery terminal? What happens with the negative connection? Can I just connect it to a local earth or must it also go to the battery negative terminal?

 

[ActiveCampers]

the earth won't need connecting back to VB, just either loop into LB earth or normal ground - as the grounds should be common. (Maybe if used in a wooden boat it would differ)
Remember appropriate fuses.
Also how are you charging the LB from the engine? If you are using a dumb relay or voltage sensitive relay you may end up in a mess - the solar puts voltage into VB and once that increases beyond 13.x the charge relay cuts in etc (!) not what you want. If you are using a B2B or D+/Key+ you may not have this issue.

(as an aside, I use a B2B charger which back-charges the VB if there is excess power - I did this as the device knows if the engine is running or not and can manage the VB charge as needed without multiple connections, and also it will then backcharge the VB from excess power from any source - solar or mains hookup. )

 

[Molly 3]

the earth won't need connecting back to VB, just either loop into LB earth or normal ground - as the grounds should be common. (Maybe if used in a wooden boat it would differ)
Remember appropriate fuses.
Also how are you charging the LB from the engine? If you are using a dumb relay or voltage sensitive relay you may end up in a mess - the solar puts voltage into VB and once that increases beyond 13.x the charge relay cuts in etc (!) not what you want. If you are using a B2B or D+/Key+ you may not have this issue.

(as an aside, I use a B2B charger which back-charges the VB if there is excess power - I did this as the device knows if the engine is running or not and can manage the VB charge as needed without multiple connections, and also it will then backcharge the VB from excess power from any source - solar or mains hookup. )

What btb unit do you use

 

[ActiveCampers]

What btb unit do you use

Votronic 1212-30
Got it from https://www.ebay.co.uk/itm/142951694427
Managed to get it with a 10% ebay code so paid £128

Works well, pulls exactly 30A and happily back charges engine when solar or mains is on (when LB > 13.4v). LiFePo4 settings are basic but work.
This keeps the LB at 13.4v (e.g. takes the "top off") overnight which is great as means the LiFePo4's aren't sitting at a high charge.

Manual online and make your own call

For me, it was the only one that met all my criteria (incl price/size)

 

[sydnsue]

the earth won't need connecting back to VB, just either loop into LB earth or normal ground - as the grounds should be common. (Maybe if used in a wooden boat it would differ)
Remember appropriate fuses.
Also how are you charging the LB from the engine? If you are using a dumb relay or voltage sensitive relay you may end up in a mess - the solar puts voltage into VB and once that increases beyond 13.x the charge relay cuts in etc (!) not what you want. If you are using a B2B or D+/Key+ you may not have this issue.

(as an aside, I use a B2B charger which back-charges the VB if there is excess power - I did this as the device knows if the engine is running or not and can manage the VB charge as needed without multiple connections, and also it will then backcharge the VB from excess power from any source - solar or mains hookup. )

I have no idea what charges the LB from the engine. I am not changing that so I assume it is whatever Elddis installed. The Truma sends excess charge to the VB when the LB has reached a percentage full.

 

[ActiveCampers]

I have no idea what charges the LB from the engine. I am not changing that so I assume it is whatever Elddis installed. The Truma sends excess charge to the VB when the LB has reached a percentage full.

Right, best to find out as well as the rest of your setup
For instance its possible that....
Solar charges LB. LB is full, charged VB. VB gets full and above a "threshhold" (eg 13.6v) and the Elddis system thinks the engine is running as voltage is high, so it cuts in and links the VB/LB together to charge - and tells your fridge engine is running so it shuts off gas and runs on 12v etc.
The two systems may work, or may conflict. Devil is in the detail as to what you currently have...... And also the spec of the trickle charge (if it keeps it under 13v you will probably be fine)

 

[marchie]

Solar charges LB and David at Wildebus fitted an Ablemail AMT12 Battery Relay/Charger that has 8 settings for smart/traditional alternators and Lead Acid/ Lithium Batteries, plus a 9th manual override option that can be used to force the LB to feed the VB for 9 seconds in every 10 seconds if the Vehicle Battery shows any sign of dropping to a voltage low enough to threaten the Airbag ECU. Proved invaluable in January when we had spells of 2 or 3 days with no Solar input, keeping the VB nicely topped up and allowing the LB to play 'catch up' on its charge when the sunlight/brightness reappears

In normal use, the AMT12 pulses up to 3 amps to the VB at 10 second intervals, the pulses lasting about 2 seconds until the VB reaches its Charging Threshold of 12.8v

Steve

 

[sydnsue]

Thanks for everyone's advice. I shall give it a try and see what happens.