EC155 psu/charger with a Ctek Battery to Battery charger

[Chris CM]

My Devon Aztec PVC is fitted with a Sargent EC155 PSU/charger.

It has 2 x 100w solar panels supplying 2 x 95Ah leisure batteries via a Victron 75/15 mppt charger, the vehicle battery is kept topped from the leisure batteries with a Sterling battery maintainer. The output to the leisure batteries, via the EC155, when the engine is running seems rather low, about 6A, I have a Ctek battery to battery charger (D250S) which would give far more efficient smart charging, up to 20A, but I’m unsure as to how to wire this with regard to the EC155’s connection to the vehicle and leisure batteries. Do you think it would be ok to parallel with the EC155 charging and connect the Ctek directly between the vehicle and leisure batteries?
Thanks.

 

[autorouter]

It's not a good idea to simply parallel them, because the EC155 has a split charge relay that directly connects starter battery to leisure battery when the engine is running. That would short out the B2B and stop it charging any faster than before.

But if you simply disconnect the starter battery, then when the engine is not running and hookup is connected, the EC155 built-in charger can't charge it.

What others have done is connect the B2B in parallel, but put a relay in the starter battery wire near the EC155 terminal. The relay coil is energised from the D+ signal from the alternator. Use a 5-terminal relay, and use the NC(Normally Closed) terminal instead of the more usual NO(Normally Open) one. It switches OFF when the engine starts, not ON like a normal split charge relay.

The D+ signal is one of the wires going to the EC155, so you can tap into that.

The result is, the starter battery is disconnected from the EC155 when the engine is running, but reconnects when the engine stops to allow hookup charging etc.

Having said all that, if you have a Sterling battery maintainer, you probably don't need hookup charging for the starter battery. In that case you could just disconnect the starter battery from the EC155 and not bother with a relay at all.

 

[Revolvor]

As autorouter has already said, it is necessary to isolate the supply from the EC155 when the engine is running, in order to get any benefit from the B2B Charger.

I fitted a CTEK D250S to my van, but made use of the fact that it also a MPPT Solar Charge controller. As you already have the Victron 75/15 Charge controller, you may be better advised to fit a dedicated B2B charger such as THIS, and to sell the CTEK unit to someone who wants to make use of its combined B2B and Solar Charge Controller capabilities.

I have attached a sketch showing how I fitted a relay to isolate the PSU when driving (I have an EC225) if you do go ahead and use your D250S.

 

[Chris CM]

Thanks guys, very useful info, seems that a relay is the way to go, Revolver, does your arrangement still allow the fridge to operate on 12v whilst the engine is running? So far I’ve only been able to find what appears to be a split charge relay next to the vehicle battery, I’m going to fit a fridge fan so may find the fridge relay next to the back of the fridge? What has confused me is that there is no separate charge relay shown on the EC155 wiring diagram only one for the fridge, so is the one next to the vehicle battery a fridge relay and not a split
charge relay? If this is the case is the leisure charge controller built into the EC155?

 

[Revolvor]

@Revolvor, does your arrangement still allow the fridge to operate on 12v whilst the engine is running? So far I’ve only been able to find what appears to be a split charge relay next to the vehicle battery, I’m going to fit a fridge fan so may find the fridge relay next to the back of the fridge? What has confused me is that there is no separate charge relay shown on the EC155 wiring diagram only one for the fridge, so is the one next to the vehicle battery a fridge relay and not a split
charge relay? If this is the case is the leisure charge controller built into the EC155?

Yes, the fridge still works on 12v when driving, because all I did was tap into the +ve fridge wire and connect it to the coil on the relay.

I don't know about the EC155 but my EC225 has an additional unit - EM50. It's an interface between base vehicle electrics/electronics and habitation electrics/electronics. It controls, among other things, split charging, auto step retraction and 12 volt fridge operation. See Attached.

That is where I accessed the +ve fridge feed.

Sargent Technical Support is good -
Sargent Electrical Support
01482 678981

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[Chris CM]

Thanks for this, it looks a lot more sophisticated than the EC155! On that the only apparent connections to the vehicle are batt + and earth. The fridge relay is shown as a discrete component outside the EC155.
Some food for thought ?

 

[autorouter]

The split charge relay, which connects the starter and leisure batteries when the engine is running, is inside the EC155. From the Sargent web site:

"The EC155 is a compact 155W power supply unit and charger and incorporates the following features. RCD & 3x MCB mains output protection, 155w Electronic Charger / Converter -Battery input fuses, multiple output fuses, built in charging & EMC relays simplifying harness and loose part count, multiple relay switching channels. This PSU interfaces directly with the EC50/EC51 Control Panel."

The connection to the fridge relay that Revolvor uses is just a convenient way to get a D+ signal. The actual D+ signal switches the fridge relay when the engine is running. The fridge relay can be used to switch another relay that disconnects the battery from the EC155. As you say, the fridge relay is external to the EC155 so is quite handy for this.

 

[Chris CM]

Thanks for this, I hadn’t seen this document extract, just the circuit diagram, all becomes clear?