Leisure battery voltage drop (1 Viewer)

[Tombola]

Is it normal to see a big voltage drop in Amps and Watts from leisure batteries when starting the engine.
Fiat Ducatto, on Imala 734.#

My BMV712 sows minus 130w or more and a drop in amps when starting just for the odd second

Thanks

 

[Richard n Ann]

Our car battery drops to 9v when cranking

It whips the engine over fast though

 

[Tombola]

thanks Richard n Ann, yeah my cab battery drops too as youd expect,( I have the battery monitor too) but my leisure batteries also drop ? judging by my BMV monitor, which I havent noticed before.
SO they are lnked just for a second.
Im guessing split charge relay or something takes a second to close.

OR is there something on there tht helps the starter battery if it needs too? via the sargent system

^{_{Subscribers  do not see these advertisements}}

 

[tonyidle]

As soon as the alternator spins the split charge / fridge relay(s) operate. Until the engine is running there's little available from the alternator so I'd expect that you're seeing the fridge drawing current from the leisure battery until the alternator takes over.

 

[andy63]

As soon as the alternator spins the split charge / fridge relay(s) operate.

Surley that depends on the parameters that operate the engine run signal.. on a ford it has to sense engine speed and a certain voltage ..definitely a few seconds before my relays operate..

The voltage drop an a start battery is acceptable down to 8 point something volts momentarily during cranking I believe..
Andy..

 

[pappajohn]

The only way I can see this happening is if the split charge relay is ignition switch triggered.
Turn on ign and relay closes connecting both batteries, crank engine and power taken from both batteries... Hab battery via relay.
Only drawback with that.... The split charge relay and wiring couldn't cope with Cranking amperage, 300/400amps through maybe 4 or 6mm cable... it would melt in a second.

^{_{Subscribers  do not see these advertisements}}

 

[Tombola]

The only way I can see this happening is if the split charge relay is ignition switch triggered.
Turn on ign and relay closes connecting both batteries, crank engine and power taken from both batteries... Hab battery via relay.
Only drawback with that.... The split charge relay and wiring couldn't cope with Cranking amperage, 300/400amps through maybe 4 or 6mm cable... it would melt in a second.

seems likely Pappajohn as it is. The same relay that controls the step/fridge I think is also the one that controls the leisure battey charge from alternator of the fiat 2019 ducatto/imala with the sargent system

 

[tonyidle]

Surley that depends on the parameters that operate the engine run signal.. on a ford it has to sense engine speed and a certain voltage ..definitely a few seconds before my relays operate..

The voltage drop an a start battery is acceptable down to 8 point something volts momentarily during cranking I believe..
Andy..

You're correct. However many vans use simple arrangements. And he is talking about the leisure battery.