question

begef avatar image
begef asked

Charging or trickle charging of starter battery (motorhome)

Charging or maintenance charging of the starter battery (motorhome)

I have seen a couple of questions/answers in the community, but to be honest the topic isn’t yet clear for me ☹.

My van (electrical) set-up:

The battery bank (2x150Ah lithium) can be charged via shore power / Multiplus 12/3000 230-16, MPPT Smart Solar 100/30 and Orion TR 12/30. All devices are equipped with a Lynx Distributor connected to the battery bank. The system will be controlled by Cerbo GX.

I would like to have the opportunity to “maintain” the starter battery (100Ah AGM) with a maintenance/trickle charge (in case that the motorhome is not in use for longer time) and to be able to “charge/support to start” the engine in case of low starter battery. The starter battery is connected to the Orion via a 16mm2 cable.

In the Multiplus description there is a port G (TR-Charge). This connector should be connected to the starter-battery-plus pole. The starter battery minus pole must be connected to the minus pole of the battery bank. The battery voltage is probably tapped/measured through the wires (?).

  • Can someone describe to me the function / mode of operation of the TR-Charge (i. e. under what conditions does it load)? Or is there any written description on Victron’s webpage (which until now haven’t found)?
  • Charging of the starter battery (motor off) takes place only when the Multiplus is in operation and / or on shore power?
  • Thus, the PV system does not contribute (?) or the current is “passed on” when the battery bank is full (but different (charging) voltages between lithium and lead (?)).
  • What wiring size is recommended for the port G (TR-charge)?
  • The "common groung" for starter and battery bank can be the van chassis?

Hope that you have already a good solution in place which you would like to share with me. Any further comments are welcome,

Frank

MultiPlus Quattro Inverter Charger
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

2 Answers
pwfarnell avatar image
pwfarnell answered ·

The detail is in here as I have written it down many times.

The trickle charge is taken directly from the main 12V supply to the Multiplus through a current limiter (to the stated 4A) and a diode to prevent the starter battery charging the domestic battery. There is no control of it, it just relies on the charging voltage on the domestic battery pushing some current through but the diode always causes an approximate 0.5V drop to the starter. If you have solar then the trickle charge will work. If the inverter is turned off the trickle charge will still work.

The one important factor is that it is designed for both the starter and domestic batteries to both be lead acid. When the charging stops, both batteries are at the same voltage and with the diode voltage drop no current flows. As you have lithium domestic batteries which are a higher voltage than lead acid then the system will continuously pass current through the starter battery discharging the lithium battery. The trickle charger will not shut off if the battery gets low right until the battery BMS isolates the battery if you have drop in batteries, but if you have a Victron simple BMS then an inverter shut down does not stop the trickle charge.

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

begef avatar image
begef answered ·

@pwfarnell Thank you for your answer. I agree that (as mentioned in my question) there are many comments regarding trickle charging. At least for new camper van building projects the domestic battery is lithium while the (truck) starter battery is still lead acid. I understand your answer like that in case of different battery types the port G is not usable. What is necessary is a microprocessor which is monitoring the different voltages and independently manage the charging like “Rapid” from WCS (www.wcs-mobilestromversorgung.de). That should be mentioned in the Multiplus documentation, guess Victron has a job to do.

What do you mean regarding “If you have solar then the trickle charge will work.” ?

2 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

pwfarnell avatar image pwfarnell commented ·
Because the trickle charge is connected directly to the input 12V from the domestic battery, anything that charges the domestic battery like solar, or a 240V powered charger will also cause the trickle charger to charge the starter battery when the domestic voltage increases.
0 Likes 0 ·
begef avatar image begef pwfarnell commented ·
Thank you for clarification :-)
0 Likes 0 ·

Related Resources

Additional resources still need to be added for this topic