Just fitted a b2b strange behaviour

[Steve and Denise]

I have just fitted a 30amp B2B on our Iveco based Carthago the van comes standard with a 16mm sq supply to the rear where the Cbe distribution DS470 board is this would normally supply up to a 50amp charge for the std batteries.
As I have fitted a lithium 300amp I thought a 30amp B2B would be a good starting point as to keep well within the limits of a 16mm cable.
So all fitted started up and bingo 30 amp charge going in at 13.5 v to the lithium 14volts supply from alternator, then alternator drops to 11.9 for 10seconds then back up to 14volts and keeps changing every 10-20 seconds.
When I check the voltage at the engine end it reads the same so not a voltage drop on the cable.
Apply a few revs and the voltage stabilises and the charger stays on with no fluctuation,
Could the alternator have a current limitation when running slow.
I have used the D+ to switch the B2B on and off and also a 40amp relay from LB to supply the Cbe for van electrics.

 

[gerry mcg]

What make B2B? (Victron?)

 

[Steve and Denise]

What make B2B? (Victron?)

Ablemail Manchester

 

[Raul]

Is it a smart alternator? If you have a shunt on the negative starter battery post it’s a smart alternator. Your B2B should be of the chassis so the shunt can account for the current, and feed the right info to the ecu to control the alternator.

 

[Steve and Denise]

Is it a smart alternator? If you have a shunt on the negative starter battery post it’s a smart alternator. Your B2B should be of the chassis so the shunt can account for the current, and feed the right info to the ecu to control the alternator.

It’s a 2018 Iveco and when I asked at Iveco dealer they said it should not be, but if it was just pull the lead from the - post on main battery

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[Raul]

Not from the starter post, have a look at the starter negative cable, if it has a shunt, then ALL your charging and loads ( negative side) should be from the chassis. Usually there is studs power take of under bonnet for this purposes.

 

[Raul]

Something like this on the negative starter battery
Broken Link Removed

Broken Link Removed

 

[Steve and Denise]

Not from the starter post, have a look at the starter negative cable, if it has a shunt, then ALL your charging and loads ( negative side) should be from the chassis. Usually there is studs power take of under bonnet for this purposes.

Yes sorry my post was not clear negative post I’ll do that tomorrow as I ran out of light today, but as I said when a few revs are applied the voltage stabilises?

 

[pappajohn]

Sounds like a smart alternator.
My Hyundai does the same....can be as low as 11.9v then shoot up to 14.8v then stabilise at around 12.9v.
70ah AGM battery less than a year old.

 

[the1andonly]

Have you disabled the cbe split charge relay?
There a few threads here about doing this on a cbe300 cutting r37?

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[Steve and Denise]

Have you disabled the cbe split charge relay?

No I have used the 50amp supply from the Cbe to the B2B then to battery and used a N/C relay across the B2B to supply hab electrics

 

[Steve and Denise]

After reading most threads on here about every model of Cbe I could not see any point in disabling the relay, as I was using that feed for my supply and not introducing a separate supply that would conflict each other. the1andonly

 

[the1andonly]

Steve and Denise you obviously know more about your system than me. I was lucky in that there is well documented info on what to do.

 

[Steve and Denise]

Steve and Denise you obviously know more about your system than me. I was lucky in that there is well documented info on what to do.

With a bit ok luck and good judgement I hope to understand it fully by this time tomorrow and of corse all suggestions and ideas gratefully received

 

[the1andonly]

With a bit ok luck and good judgement I hope to understand it fully by this time tomorrow and of corse all suggestions and ideas gratefully received

Hope you get it sorted

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[Steve and Denise]

Hope you get it sorted

I will post my findings if only to help others with the wealth of information that CBE.it seem to be reluctant to reveal to the end user and most dealers have either no clue or can not be bothered

 

[Steve and Denise]

Ok had a look this morning and yes there is a shunt on the negative terminal now disconnected but the alternator voltage still fluctuates on tick over up the revs slightly and the voltage stabilises in the vehicle and the B2B stays on

 

[Raul]

Sounds normal, ecu controls the alternator. Once demand increases, so the alternator output.

 

[Steve and Denise]

I have just spoken to someone who fits this type of b2b on Ivecos and has had similar results on tick over also the manufacturer says it will be the alternator and switching on and off can’t damage the unit.
Thanks for all your input everyone