Split Charge Relay Question

[ShropsWindowCleaner]

Hi all. Hope everyone’s day is going well! Quick question about my SCR. When the engine is running the main van battery correctly reads around 14.2v. However my leisure battery connected via the SCR reads 13.2v with the engine running. Is this normal? Or should it be higher? Thank you in advance for any advice.

 

[ched999uk]

If it's just a basic split charge relay then I would expect the leisure battery to read a similar voltage when the engine is running. If your vehicle has a 'smart' alternator then it really needs a battery to battery charger as the alternator doesn't quite work like an older non smart one.
First thing to do is check all connections - scr and leisure battery both +ve and -ve sides and both ends of each cable. Ideally use a multimeter to check for voltage drop.
I assume that the leisure battery voltage does go up when you start the engine?

 

[WindyinNorfolk]

As above really - if its an old fashioned alternator and your getting 13.2 you will need to check connections or use a better gauge wire

 

[ShropsWindowCleaner]

Thanks for those helpful replies. I’ve checked all the connections and the positive terminal on the van battery looks corroded. Could this be the issue? Il clean the connection up tomorrow, probably pop a new connecter on it, and test.

 

[ched999uk]

Thanks for those helpful replies. I’ve checked all the connections and the positive terminal on the van battery looks corroded. Could this be the issue? Il clean the connection up tomorrow, probably pop a new connecter on it, and test.

Could well be causing high resistance which might be the cause of lower voltage at the leisure battery.

 

[Deleted member 7446]

Hi all. Hope everyone’s day is going well! Quick question about my SCR. When the engine is running the main van battery correctly reads around 14.2v. However my leisure battery connected via the SCR reads 13.2v with the engine running. Is this normal? Or should it be higher? Thank you in advance for any advice.

Unless you are driving 100 miles a day or long journeys for more than two hours at 2500rpm a split charge system won't maintain a battery.

Solar PV is the best way or home hook up to a high quality leisure battery charger with 15 amps minimum and float charge capable

 

[spruce]

Hi all. Hope everyone’s day is going well! Quick question about my SCR. When the engine is running the main van battery correctly reads around 14.2v. However my leisure battery connected via the SCR reads 13.2v with the engine running. Is this normal? Or should it be higher? Thank you in advance for any advice.

As has been stated, a split charge relay is a direct on-off switch which connects and disconnects your leisure battery to the starter battery. Whatever the volt reading is at the starter battery side should be the same voltage at the leisure battery side.

If there is a difference then there is either a bad connection somewhere along the cable, at the leisure battery terminal, a damaged cable or a failing scr. First stop is to clean up that corroded battery connector so it makes a good connection.

With a multimeter, you need to follow the cable from the battery and take readings as you go. First stop is the fuse near the starter battery on both sides of the fuse.
Then to the split charge relay. You may need to unscrew it from it's mounting to get to the terminals underneath.
Then at the fuse before the leisure battery.

Most split charge relays are 140amp Durite ones or copies and seem very robust. But it doesn't guarantee this has failed. Depending on the cable length, we have found the 110amp 16mm cable is best, although one supplier did supply 70amp cable with the first vsr (voltage sensing relay) I purchased.

One of the other issues could be at any of the battery cable eye lugs. These are usually crimped to the cable with shrink wrap tubing over them. If you get 14.2v at the eye lug after the fuse or at the scr, it doesn't mean that you don't have a faulty cable connection at that lug.

You may find this helpful. https://carcody.com/battery-terminal-corrosion/

 

[PC]

Unless you are driving 100 miles a day or long journeys for more than two hours at 2500rpm a split charge system won't maintain a battery.

Solar PV is the best way or home hook up to a high quality leisure battery charger with 15 amps minimum and float charge capable

40 mins in to work 40 mins home. Using the same split charge from about 5 years ago and the same battery. I think the split charge is a smartcom one that cost me about £30

 

[Deleted member 7446]

40 mins in to work 40 mins home. Using the same split charge from about 5 years ago and the same battery. I think the split charge is a smartcom one that cost me about £30

I've got a durite however short start stop journeys kill starter batteries hence why I also have solar and mains hookup

 

[WindyinNorfolk]

There is a lot of variables here - the info given is sound but the individual may require extra charge over night - sometimes never - in the first six years I never required extra charging - my work days were not overly busy and I travelled around 20 miles a day - this kept everything charged up - then big works came rolling - 5 hours at one site - boy did that battery need extra charging - now most of the vans get to Friday without extra charge but we do leave them on charge over the weekend - so people need to see what suits them to go along side their workload.

Ive now got 2 vans with 'smart' alternators - I hate them - its getting complicated for me to understand

 

[Deleted member 7446]

There is a lot of variables here - the info given is sound but the individual may require extra charge over night - sometimes never - in the first six years I never required extra charging - my work days were not overly busy and I travelled around 20 miles a day - this kept everything charged up - then big works came rolling - 5 hours at one site - boy did that battery need extra charging - now most of the vans get to Friday without extra charge but we do leave them on charge over the weekend - so people need to see what suits them to go along side their workload.

Ive now got 2 vans with 'smart' alternators - I hate them - its getting complicated for me to understand

As @spruce often quotes "knowing the correct numbers IE voltage and the minimum discharge threshold is key as ive seen many new starters hammer their battery to 4v before as they think they can just recharge it again which is absolutely incorrect.

You've been lucky to not experience any issues but like you say, variables differ

 

[ShropsWindowCleaner]

Thanks for your extremely informative replies everyone! I really appreciate it. It’s given me some detective work to do. I’ve also read, just to add this to the mix, that certain SCR’s will sit at 13.4v on the leisure battery side, when the leisure battery is full, and then increase the voltage when it needs charging……
My leisure battery is currently measuring 12.9v when the engine is off, so perhaps i’m getting a reading of 13.4v from the SCR because the leisure battery is full?

 

[spruce]

Thanks for your extremely informative replies everyone! I really appreciate it. It’s given me some detective work to do. I’ve also read, just to add this to the mix, that certain SCR’s will sit at 13.4v on the leisure battery side, when the leisure battery is full, and then increase the voltage when it needs charging……
My leisure battery is currently measuring 12.9v when the engine is off, so perhaps i’m getting a reading of 13.4v from the SCR because the leisure battery is full?

Please advise where you read that.

A sophisticated battery to battery charger will go into float mode at a reduced voltage to keep a battery fully charged.
A basic SCR will not do that. It is just an on/off switch.

A voltage sensing relay that 12v Planet on Ebay sell will activate when it senses the current from the alternator reaches 13.3v. Once it has been activated, then the voltage on either side of the relay will be exactly the same, unless there is an internal fault in the relay. I have run a scr and a vsr for years and have never seen a voltage difference on either side of the relay.

A basic split charge relay is either activated via the vehicle's alternator or the vehicle's ignition switch. Switch the ignition off or switch the engine off, and the relay immediately disconnects or separates the starter and the leisure battery.

To test a leisure battery's state of charge, the battery needs to be rested for at least 4 hours before you take a reading.

 

[ShropsWindowCleaner]

SCR update: I took it to a professional. All sorted now. Diagnosed as a bad earth connection, two connections were made the wrong way round, and the type of wire from van battery to SCR was incorrect for voltage needed. Im happy to report SCR is now reading the same as the van battery. Thank you all for your awesome advice! Always learning in this game

 

[Deleted member 7446]

SCR update: I took it to a professional. All sorted now. Diagnosed as a bad earth connection, two connections were made the wrong way round, and the type of wire from van battery to SCR was incorrect for voltage needed. Im happy to report SCR is now reading the same as the van battery. Thank you all for your awesome advice! Always learning in this game

I've seen many so called automotive electrician's and self confessd caravan camper experts use cable less than 16mm² for this application

The durite SCR has a short earth bond wire which you can also add a secondary connection to another part of the chassis to ensure correct terminations.

If done correctly its rare to ever experience any issues

Mine just does it its thing and I've never had a problem with it