Adding a ctek charger - to just leisure battery or both?

[Tinium]

Hi all,

Can't quite find the answer in the search, so apologies if this has been asked before

Looking to add a ctek 5.0 charger to keep my leisure battery topped up when I'm on site with a hook-up. But should I just wire it direct to the leisure battery, or is there any advantage to wiring it to the main battery, and then letting my existing split-charge setup keep both batteries topped up?

Cheers,
Ben.

[bigherb]

Only connect it to the leisure battery. The charger can only charge one battery at a time, if charging two batteries then it will overcharge one if they are not both discharged to the same level and are not the same size/capacity, age.

[Tinium]

Thanks bigherb,

Will keep it simple for now then with the 5.0, and look into the 250S & Smartpass when I get round to fitting solar & ditching the old Zigg unit at some point

What you say about the different batteries/charge state makes sense - I've seen a few different systems with banks of batteries charged from a single supply, but they're always just the leisure bank, not the main vehicle battery, so that explains that.

Cheers,
Ben.

[lodgey62]

Why doesn't this happen when the alternator does the charging?

[bigbadbob76]

Why doesn't this happen when the alternator does the charging?

Because the alternator is regulated to 14-14.5v and the vehicle battery is designed to handle that continously.
proper Leisure batteries don't last well if you charge them continuously.
don't just use a split charge relay for AGM or deep cycle batteries, they should have a charge controller in the circuit.
The charge controller monitors the current and voltage during charging and if one battery is at a different charge level than the other then that confuses the controller and it can overcharge the higher level one.
Cheap leisure batteries are just heavy duty vehicle batteries and can be charged with just a split charge relay without damage.
They don't like deep discharge though and won't last many charge cycles if you do flatten them.
Hope that helps and makes sense.

[Mark S]

I read that lead/acid batteries do not like being cycled and last best when 'floated' at a moderate Voltage (13.7, say). Clearly when you are driving your van the alternator is putting out well over 14V, but this is only for limited durations and may drop depending on how many devices are in use. Putting in too much voltage for too long can boil the battery acid dry eventually.

When parked, I use a Ctek 10A smart charger https://www.amazon.co.uk/CTEK-MXS-10-8- ... B005O8YG44 connected to the leisure battery only. This provides a reconditioning cycle before going into float mode indefinitely. The 10A gives enough muscle to power additional accessories (lights, stereo etc) also connected to the leisure circuit while at a campsite. (It can also be set to power-supply mode explicitly).

Because the Ctek has only got one set of outputs, in order to ensure the engine battery gets floated also I installed a Battery Master https://www.vanbitz.com/product/battery-master/ between the leisure battery and engine battery. This diverts some charge to the secondary whenever the voltages differ (by 0.5V IIRC). By using unpluggable connectors I can reverse the batteries if I choose, so the engine battery gets the smart charge and the leisure battery gets sloppy seconds. However, I have never bothered doing this. I can also easily take out the whole charger to use elsewhere, as it is held down by Velcro.

These two devices fit in the space under the seat that used to house the now-redundant BBB charger, and take up far less space. I built a little wooden cover to protect them from kit stowed on top.

I have left this set-up plugged in all the time at home since 2012. I have had my current leisure battery since 2009 and it is still going strong; I replaced my engine battery last year for the first time since 2004.

(E D I T: when the engine is running, the split-charge relay closes and both batteries are effectively connected as one, bypassing the Battery Master and rendering it redundant). It would be a smart move to knock out your Ctek by unplugging the hook-up cable etc before starting the engine).