2 x Leisure Batteries and Split Charger Relay

[Oliver.m]

Hello everyone,

 

First of all thank you for reading this. Please get some popcorn (or beer / wine), take a seat and if you are lucky you will be still awake at the end of this post.

 

I am struggling to get my head around two topics that have been discussed in depth in this and other forums.

 

First Topic is related to "two leisure batteries in parallel"

Second Topic is related to "split charge relay"

 

The more I read the more I know and the more I doubt and think...

 

But let’s start from the beginning:

 

My partner and myself have handed our notice’s in and will leave our office jobs to travel the UK as well as Europe in our van. This is planned for an unspecified amount of time (until there is no money left) and will be a mix of wild camping and campsites.

 

A few months ago, we bought a 2001 Fiat Ducato 2.8 JTD Bilbo Campervan conversion with a propex heating system, a dometic fridge freezer, water heater (works only on hookup) and a water pump. It came with the original PMS3CD – Unit and 2 aftermarket 85ah leisure batteries fitted. One under the passenger and the other under the driver’s seat. After emailing the manufacturer “Bilbos”, they confirmed that the Van left their building in 2001 with only one leisure battery. This means the second battery has been fitted afterwards.

 

Both batteries are deeply discharged and have probably suffered permanent damage as they do not hold charge. I suspect they have not been looked after properly and as the PMS3CD “only” creates 13.07V when on hookup, it’s not enough to get them to 100% charge. (Please correct me if I am wrong) We have fitted 2 new batteries NUMAX DC31MF at 105 AH each to replace those. (Resting Voltage settles at 12.8V when not connected to the van). The plan is to use the NUMAX connect and forget charger to keep them well charged as we go as the PMS3CD will not be able to charge them to 100% at 13.07V.

The actual fitting of both batteries looks good to me, which has also been confirmed by an auto electrician that we called out recently to review this. (90 quid for a bit of advice and fault finding)

 

He confirmed it was wired up correctly and not too much voltage is lost through caballing and resistance from the alternator supply (from memory 14.38V arriving at leisure batteries). In all fairness he found the problem we had with our PMS3CD unit at that time (Battery selector Rocker Switch was faulty) and saved us replacing the unit.

 

(>) Now to my first topic:

The leisure battery A has been connected to the positive cable coming from the split charge relay and the negative to the chassis. Leisure battery B has then been added with positive to positive and negative to negative onto Leisure battery A. After reading the Article from the Caravan Chronicles I am confused. The electrician said the way it is currently wired up currently is correct, and the article says its not correct and will cause long term problems.

Is the auto electrician right or the article?

 

Article see here: https://caravanchronicles.com/guides/how-to-connect-two-batteries-in-parallel/

Please be advised it is a very easy change to move the earth from Leisure Battery A to Leisure Battery B.

 

(>) Topic number two.

Infront of the Leisure Battery A is a Durite 0727 – 18 12V 180AMP split charge relay which seems to work fine.

However, as soon as I connect my two new leisure batteries to the system, the voltage of those batteries drops from 12.8V to 12.6V. I assume this is due to the cut out voltage of the split charge relay being at 12.6V. As the resting voltage of the two new batteries is above 12.6V it opens and connects all three (1x vehicle battery, 2x leisure batteries). This results in equalized voltage of all three batteries and probably. The main van battery has a resting voltage of 12.53V.

 

I do not want to ignore this problem and find a clean solution if possible. As our plan is to go travelling in the van fulltime very soon. (Solar panel is in consideration too if that might change things...)

 

To me it sounds like a new split charge relay with a higher cut out voltage would be the route to go. I found one on 12volt planet that cuts out at 12.8V which sounds ideal.

 

https://www.12voltplanet.co.uk/voltage-sensitive-relay-12v-140a.html?gclid=Cj0KCQjwh_eFBhDZARIsALHjIKf1tD6u-6DDYZ-T5P-zczNws7KrnOqoW75ADjPaLyDr7JZZdEdjl8waAsihEALw_wcB

 

However, it cuts in at 13.8V which the PMS3CD on hookup would never supply.

This tells me that when I am on hook-up, in order to charge the leisure batteries 100% they have to be charged with my NUMAX connect and forget charger. I presume if I connect the NUMAX connect and forget charger the relay will open and I will charge all three batteries?

 

The worry I have is that the that the NUMAX connect and forget charger is not strong enough to charge all batteries simultaneously to 100% and might create issues with equalizing charge etc. In that case, would it make sense to put an isolator switch between relay and Leisure batteries, so I can isolate them and only charge the leisure batteries if I wish to?

 

Any ideas on the above?

 

Thank you for still being awake.

 

Best wishes,

Oliver

 

[mikefitz]

For modest charging and discharging currents it wont matter if the two batteries are connected 'diagonally' or not, provided suitable cable is used to make the parallel connections.

What is perhaps more important is that the batteries are fused as near as practical to the battery positive poles, no cable should be connected to the battery positive without a suitable fuse. Where the two batteries are installed next to one another with a short link often only a single 'master' fuse is used. Where the batteries are installed some way from each other a fuse is needed for each.

 

For the VSR i suggest the Victron Cyrix,

https://www.12voltplanet.co.uk/victron-cyrix-ct-voltage-sensitive-relay-battery-combiner-1224v-120a.html?gclid=EAIaIQobChMI65m9z6WG8QIVDLTtCh3AsAyzEAQYASABEgIlbPD_BwE

 

This has a time element added to the switching thresholds that gives a better performance.

 

This VSR and your existing unit are bi directional and will connect the engine battery to the leisure battery when the voltage threshold is reached. When the leisure batteries are under charge and the voltage reaches the VSR threshold, the engine battery will be added in circuit. If the engine battery is in good condition it will be is a high state of charge and will 'divert' only a small amount of charge that the leisure batteries are receiving, thus having little impact in leisure battery charge time. Lead acid batteries connected in parallel quite happily 'share' the charge, ( unless one is faulty or well past its replace by date).

If you have the slightest reservation about the engine battery I suggest its replaced.

 

The PMS3 built in power supply /charger is nominally set to 13.8 volts, ( if its still working). Whilst this voltage will give a maintaining charge to the batteries it will take forever to fully charge. If you add a NUMAX connect and forget charger this will help, providing the output is 10A or ideally greater.

 

Adding solar is something you should consider.

 

A 2001 van may have had several owners and its probable the electrical system has been modified over time. The usual problems that arise are unsuitable cable and fusing.

 

I will try to add a typical diagram of a VSR system indicating where fuses should be positioned. The fuses should be installed as close to the high power source as practical, the batteries.

 

Mike

[mikefitz]

PMS3 with Cyrix

[spirou]

I will just add some further reading https://www.victronenergy.com/blog/2019/09/03/wiring-unlimited/

 

And a suggestion to get the Cyrix Li-ct model as it has a higher connect/disconnect voltage treshold than the standard unit. This way the batteries will definitely be connected only when either is on charge, rather than some (rare) cases where resting voltage is close or even higher than treshold thus unecessarily draining them down a bit. Plus, it's somewhat futureproof in case a lithium battery is added at a later date (not as simple as that but...)

[Oliver.m]

Hello Both,

 

thank you very much for taking the time to comment on the above. Much appreciated.

 

I have taken the advice, bought the Victron Cyrix Relay as well as two additional fuse holders to be implemented as close as possible to both positive poles. I am planning to install it over the weekend and thought I ask you about the connections 85 and 86 which are not clear to me yet.

 

They are referenced as "85 Start Assist" and "86 BAT -"

 

Looking at the drawing above in conjunction with the PMS3, the "86 BAT -" is the only one to be connected, however if I check my current set up with the durite relay, I have a orange "smartcom" box in there.

 

What is this orange box doing? Is it the fridge relay?

 

And most importantly do I have to connect this the same way again?

 

Thanks a lot in advance.

 

Oliver

[Alanb]

I suspect that the system has been uprated when the second habitation battery was added.

 

The orange Smartcom device, is an intelligent voltage sensing split charge relay rated at 30A.

 

The Durite relay is a 180A (max) make/break relay. It is not voltage sensing.

 

It is difficult to be certain of the wiring from the Oliver's photo. The Smartcom relay seems to have been repurposed to control the Durite relay, but can then only monitor the starter battery voltage.

 

The start assist on the Victron Cyrix relay, is just what it says. By adding a push button to the habitation battery +ve, the relay may be operated to allow the habitation battery to assist with engine starting in emergency, If this facility is to be used, it is preferable that the habitation batteries are of the dual purpose type (somtimes denoted marine), rather than plain leisure batteries with no CCA rating.

 

I am surprised and concerned, that Victron seem to have ignored the generally accepted Bosch convention for denoting automotive relay coil terminals. In standard usage 86 denotes the +ve terminal, and 85 denotes the -ve terminal.

 

Alan

[Oliver.m]

Hello everybody,

 

thanks again for all your help.

 

Just to summarize, I have now updated the system with the Victron Cyrix Relay. I have removed the orange smartcom box and it seems to work perfectly fine.

 

The fuses will be installed this weekend.

 

Best wishes,

Oliver