Split Charge Relays

[Timetraveller]

I'm contemplating purchasing a 70 - 100 amp intelligent split charge relay to fit to our Avondale SeaScape 5ELX. We usually 'wild camp' so having our leisure batteries in tip top condition is a must. We have two 85 amp/hr batteries in parallel; sited under the rear side bench seat. Will this relay be strong enough to do the job? We usually do not stay longer than two nights in any one place; though sometimes we do not travel far as we 'Go for a walk' in our motorhome. Unfortunately I'm restricted in how far I can walk - so we 'walk in the motorhome'.

Do these relays really boost leisure batteries as quickly as I'm led to believe? How can I monitor the charging so the batteries do not over-heat?

I shall have the unit fitted by my local garage who usually deal with my vehicle servicing as my DIY skills are not very good & I don't wish to see my pride & joy literally going up in smoke!!! But I would really like to be able to leave our generator at home as it takes up some of our payload & space.

Are there any pitfalls I should know about?

Thanks in anticipation of your help. :-D

[Brambles]

Can you post details of the Intelligent split charge relay you intend to use please and then answers can be more specific and accurate.

Jon.

[Andy_C]

70 to 100 amp should certainly be 'strong enough' but I'm not sure that, if it is just a split charge relay, it will do anything to boost the charging.

 

As Brambles says - more details please!

 

Andy

[Guest Peter James]

Easiest way is to fit a voltage sensing relay like this http://www.rawcomponents.co.uk/relays-holders/12v/200-amp-12v-relay.html

 

I have one and with the standard 160 amp alternator on the X250 van the leisure battery charges very quickly indeed, as I have used 25mm2 cable (to terminals 87 and 30 on the relay, and the negative earth cable for the batteries) and omitted the fuses, making certain the cables are very well protected to avoid any chance of shorting. Up to about this point, the thicker the cable you use to connect it up, the better it will work. Things like fuses will create voltage drop and slow it down, but if you do omit the fuses like I have, be sure the positive cable is very well protected so it cannot short out.

(the control wires to terminals 85 and 86 should still be ordinary thin wire with a fuse in)

 

 

 

[Brambles]

Peter,

Do you know something I do not know? Does the Avondale Seascape Motorhome not already come with a split charge relay already controlled from the D+ alternator output. Your circuit does not achieve anything more than a standard split charge relay circuit.

 

 

p.s. Ommitting the fuses is not a good idea at all. If you get a short circuit battery you could weld the relay contacts together and over heat them to the point you risk a fire. Fit fuses, they will not drop a significant voltage to make a difference. Remeber the main controlling factor liniting the charge rate is the leisure battery itself and the chemistry of how it works. An extra 0.1 or 0.2 of volts is not going to make much difference.

 

Back to fuses again, whaT happens in youR circuiT if the relay contacts weld togeher, not a unknown and common fault, and you start your engine? You draw heavy curremt through teh realy and wiring. So pleasew for safety which must always have priority fit a fuse. Having evne havily insulated cables runing trough your cab area is crazy without protection as in the event of an an accident you could end with one being shorted to ground and discharging the batteries at a very high rate. Having this happen in your engine compartment is one thing, but in habitation area is a no no. So entirely up to you the choice you make and how you justify but WRONG to tell others of the suggestion to leave out fuses.

[Clive]

I cannot see the attraction of an "intelligent" relay. The basic split charging circuit using a heavy duty relay and stout cable will do just as well without any technology??

http://www.motts.org/SPLIT%20CHARGING%20SYSTEM.htm

 

C.

 

 

[Guest Peter James]

Brambles - 2010-10-24 2:16 PM

 

Peter,

Do you know something I do not know? Does the Avondale Seascape Motorhome not already come with a split charge relay already controlled from the D+ alternator output. Your circuit does not achieve anything more than a standard split charge relay circuit.

 

 

p.s. Ommitting the fuses is not a good idea at all. If you get a short circuit battery you could weld the relay contacts together and over heat them to the point you risk a fire. Fit fuses, they will not drop a significant voltage to make a difference. Remeber the main controlling factor liniting the charge rate is the leisure battery itself and the chemistry of how it works. An extra 0.1 or 0.2 of volts is not going to make much difference.

 

Back to fuses again, whaT happens in youR circuiT if the relay contacts weld togeher, not a unknown and common fault, and you start your engine? You draw heavy curremt through teh realy and wiring. So pleasew for safety which must always have priority fit a fuse. Having evne havily insulated cables runing trough your cab area is crazy without protection as in the event of an an accident you could end with one being shorted to ground and discharging the batteries at a very high rate. Having this happen in your engine compartment is one thing, but in habitation area is a no no. So entirely up to you the choice you make and how you justify but WRONG to tell others of the suggestion to leave out fuses.

 

I thought I made it clear you have to make sure the cable is sufficiently well insulated that it doesn't short out? (unless the vehicle is so decimated it won't matter)

If the relay contacts welded together that would simply connect the leisure battery and vehicle battery together permanently. As I have used heavy cable the worst that can happen is that you drain your vehicle battery as well as your leisure battery. Fitting fuses probably wouldn't make any difference.

 

You generally find those who fit all these fuses then can't understand why their leisure battery takes forever to charge,

[Guest Peter James]

Clive - 2010-10-24 2:58 PM

 

I cannot see the attraction of an "intelligent" relay. The basic split charging circuit using a heavy duty relay and stout cable will do just as well without any technology??

http://www.motts.org/SPLIT%20CHARGING%20SYSTEM.htm

 

C.

 

 

2 reasons:

1) The problem of finding the D+ wire and running a wire from it. Try getting to the alternator and connecting a wire to it on the X250 van for instance (not the motorhome version with the optional bodybuilders plug fitted). Judging from the OP's post I guessed he is looking for something easy to fit?

2) I read that adding to the D+ wire can upset the ECU.

 

PS: Wiring to the D+ will connect the leisure battery as soon as the alternator starts turning. A voltage sensing relay will prioritise the main battery, by not connecting the leisure battery until a predetermined voltage has been reached.

 

[Clive]

One can always connect it to the alternator W terminal with a diode in series and fit a diode across the relay coil to stop it from chattering.

Voltage sensing systems are fine in theory but in practice the conventional split charging technique is simple and effective with very similar results once the alternator starts charging.

 

But I accept that finding the required wire inside the Fiat dash could be a problem. Personally I have always gone direct to the alternator terminals for both D+ and B+ connections.

C.

 

[tonyishuk]

Plan B, A little more expensive, but probably gives a better job in the long run.

 

http://www.outandaboutlive.co.uk/forums/forums/thread-view.asp?tid=19685&posts=22

 

Rgds

 

PS Anyone one here know how to do the "link" THING ?

[Brambles]

I will repeat again,

Do not feel tempted to omit the fuses if fitting a relay. If te battery sould fail with a short circuit you can gat excessive curremts whoh wil weld teh relay contacts together, fuses ill not blow and when you stop teh engine wil discharge the engine battery, or vica versa. Fit the fuses.

I have not been in the indsustry designing electrical sytems for vehicles for over 30 years to argue a point. Fuses will not drop a significant voltage except when the current is very high and it will not be except under fault conditions.

 

There is also a flaw in using an intelligent relay switching in when voltage of main battery has recahed a certain level, if the second battery is low on charge than it will start charging at far too high a rate with 14.4 volts being applied and not do it much good.

 

p.s. Accident also includes things like shorting a battery terminal or relay terminal to the chassis with a spanner or some other item falling on it.

Also you may have clamped your batteries securely but the next owner might not, and does not take much to make the battery fly pulling the leads with them.

[Guest Peter James]

Clive - 2010-10-24 4:54 PM

 

One can always connect it to the alternator W terminal with a diode in series and fit a diode across the relay coil to stop it from chattering.

Voltage sensing systems are fine in theory but in practice the conventional split charging technique is simple and effective with very similar results once the alternator starts charging.

 

But I accept that finding the required wire inside the Fiat dash could be a problem. Personally I have always gone direct to the alternator terminals for both D+ and B+ connections.

C.

 

True. But when someone posts 'My DIY Skills are not very good' I can't see an easier option than a voltage sensing relay, can you?

(Or a cheaper option if he is paying by the hour to have it fitted)

[Brambles]

tonyishuk - 2010-10-24 5:26 PM

 

Plan B, A little more expensive, but probably gives a better job in the long run.

 

http://www.outandaboutlive.co.uk/forums/forums/thread-view.asp?tid=19685&posts=22

 

Rgds

 

PS Anyone one here know how to do the "link" THING ?

 

 

Click Here for how to shorten links

 

[Brambles]

Peter James - 2010-10-24 5:56 PM

 

Clive - 2010-10-24 4:54 PM

 

One can always connect it to the alternator W terminal with a diode in series and fit a diode across the relay coil to stop it from chattering.

Voltage sensing systems are fine in theory but in practice the conventional split charging technique is simple and effective with very similar results once the alternator starts charging.

 

But I accept that finding the required wire inside the Fiat dash could be a problem. Personally I have always gone direct to the alternator terminals for both D+ and B+ connections.

C.

 

True. But when someone posts 'My DIY Skills are not very good' I can't see an easier option than a voltage sensing relay, can you?

(Or a cheaper option if he is paying by the hour to have it fitted)

 

James, he must already have a split charge relay circuit or similar. Look up his Motorhome model.

[Dave Newell]

Why not fit a Sterling or CTEK battery to battery charger? Sterling do a 50 Amp four stage unit and CTEK do a 20 Amp four stage unit. Both will give a much better charge regime to the leisure batteries than a simple relay no matter what current it can handle. And ofr what its worth I totally agree with Brambles, fit fuses!! If you use maxi fuses then the voltage drop caused is negligible, if you fit fuses and a smart B2B charger from either Sterling or CTEK then the voltage drop caused by fuses can actually be ignored.

 

D.

[Brian Kirby]

The OP's vehicle is a motorhome, so presumably already has a split charging facility installed.  He appears to think this "intelligent relay" will boost the charge rate to his leisure battery. 

Being a bear of little brain, I fail to see how the benefit can be any more than marginal, mainly due to stouter wires and lower resistance on the contacts. 

So, before we all start scratching each other's eyes out, are we quite sure he isn't confusing an intelligent relay with a B to B charger, which would enhance the charge rate to the leisure battery, as he appears to require?  Just asking, mind.  :-D

[Brian Kirby]

Dave Newell - 2010-10-24 7:27 PM Why not fit a Sterling or CTEK battery to battery charger? Sterling do a 50 Amp four stage unit and CTEK do a 20 Amp four stage unit. Both will give a much better charge regime to the leisure batteries than a simple relay no matter what current it can handle. And ofr what its worth I totally agree with Brambles, fit fuses!! If you use maxi fuses then the voltage drop caused is negligible, if you fit fuses and a smart B2B charger from either Sterling or CTEK then the voltage drop caused by fuses can actually be ignored. D.

Well spotted Dave!  Give this man the Kewpie doll!

[tonyishuk]

Brambles - 2010-10-24 6:06 PM

 

tonyishuk - 2010-10-24 5:26 PM

 

 

PS Anyone one here know how to do the "link" THING ?

 

 

Click Here for how to shorten links

 

Many thanks !

 

Rgds

[Brambles]

Brambles - 2010-10-23 10:34 PM

 

Can you post details of the Intelligent split charge relay you intend to use please and then answers can be more specific and accurate.

Jon.

 

 

Now you can all see why I posted the above (2nd thread post).

[Guest Peter James]

Brambles - 2010-10-24 5:42 PM

 

I will repeat again,

 

Well I won't. I have already said you have to make sure your insulation is good enough so the leisure battery cannot short out. Just like vehicle manufacturers fit the main battery without fuses.

 

Brambles - 2010-10-24 5:42 PM

 

Do not feel tempted to omit the fuses if fitting a relay. If te battery sould fail with a short circuit you can gat excessive curremts whoh wil weld teh relay contacts together, fuses ill not blow and when you stop teh engine wil discharge the engine battery, or vica versa. Fit the fuses.

 

Would have to be something pretty spectacular to weld together the contacts of a 200 amp relay? What did you have in mind?

 

Brambles - 2010-10-24 5:42 PM

 

There is also a flaw in using an intelligent relay switching in when voltage of main battery has recahed a certain level, if the second battery is low on charge than it will start charging at far too high a rate with 14.4 volts being applied and not do it much good.

 

How can that be very different to all the surplus alternator current going into the main battery on its own when that is low, which the vehicle manufacturer will have designed for? (the batteries will be connected together in parallel so the charging system will be reading their combined voltage)

 

I have been using a voltage sensing split charge relay for over a year now. It works very well, with the leisure battery charging as rapidly as you would expect the main battery to charge. I am not one of the stream of people posting on forums like this asking why their leisure battery takes forever to charge, and being sold expensive unnecessary overcomplicated chargers.

[lennyhb]

Brambles - 2010-10-24 6:06 PM

 

tonyishuk - 2010-10-24 5:26 PM

 

Plan B, A little more expensive, but probably gives a better job in the long run.

 

http://www.outandaboutlive.co.uk/forums/forums/thread-view.asp?tid=19685&posts=22

 

Rgds

 

PS Anyone one here know how to do the "link" THING ?

 

 

Click Here for how to shorten links

 

Easy way is to to use the "Insert Hyperlink" in your Word Processing or HTML editing program. You can do it in Word, Open Office & numerous other programs.

 

 

[Derek Uzzell]

The voltage-sensing relay referred to by Peter James seems to replicate the ‘coupler/separator’ battery charging arrangement that is the norm for Continental-European-built motorhomes. This has possible technical advantages over the UK-norm split-charge relay set-up, but, if a motorhome has already been fitted with a satisfactory split-charge relay system I really can’t see any genuinely useful gain in messing about with that system to use a voltage-sensing relay instead (or, indeed, vice versa).

 

It's another matter if a vehicle with just a ‘starter battery’ is to be modified to include a ‘leisure battery’ system. Then it clearly makes sense to decide at that point whether the battery-charging arrangement that’s to be installed should be ‘normal’ UK-style or Continental-style, or something more high tech.

 

Timetraveller’s original posting indicates that, despite having 170Ah-worth of leisure batteries and usually only wild-camping for no more than two days, he apparently still finds a need for a generator. This suggests that he is using an awful lot of 12V power during his relatively short off-230V-hook-up stops and/or that the distances driven between the stops are generally so short that the vehicle’s alternator cannot adequately recharge the leisure batteries.

 

Assuming that the SeaScape’s original split-charge relay-based system is functioning properly, I don’t believe a simple voltage-sensing relay alternative will help. Dave Newell’s suggestion of fitting a battery-to-battery charger should optimise leisure-battery charging, but won’t be particularly cheap, neither would opting for ‘free’ charging using solar or wind power.

 

Personally, before considering changing anything, I’d want a) to know what the present charging system is capable of putting into the leisure batteries and b) to analyse how the motorhome is being used and explore whether there’s any easy means of reducing the heavy 12V current drain - for example, replacing filament light bulbs with LED equivalents.

[Brambles]

Peter James - 2010-10-25 5:24 AM

 

Brambles - 2010-10-24 5:42 PM

 

I will repeat again,

 

Well I won't. I have already said you have to make sure your insulation is good enough so the leisure battery cannot short out. Just like vehicle manufacturers fit the main battery without fuses.

 

Brambles - 2010-10-24 5:42 PM

 

Do not feel tempted to omit the fuses if fitting a relay. If te battery sould fail with a short circuit you can gat excessive curremts whoh wil weld teh relay contacts together, fuses ill not blow and when you stop teh engine wil discharge the engine battery, or vica versa. Fit the fuses.

 

Would have to be something pretty spectacular to weld together the contacts of a 200 amp relay? What did you have in mind?

 

Brambles - 2010-10-24 5:42 PM

 

There is also a flaw in using an intelligent relay switching in when voltage of main battery has recahed a certain level, if the second battery is low on charge than it will start charging at far too high a rate with 14.4 volts being applied and not do it much good.

 

How can that be very different to all the surplus alternator current going into the main battery on its own when that is low, which the vehicle manufacturer will have designed for? (the batteries will be connected together in parallel so the charging system will be reading their combined voltage)

 

I have been using a voltage sensing split charge relay for over a year now. It works very well, with the leisure battery charging as rapidly as you would expect the main battery to charge. I am not one of the stream of people posting on forums like this asking why their leisure battery takes forever to charge, and being sold expensive unnecessary overcomplicated chargers.

 

Manufactures fit fusible links, can be in the terminals themselves, built into the cables or a seperate fusable link cable. Whatever the cables are acually protected.

 

Relay contacts can weld togther for a number of reasons. From sparking/arcing, mechanical failure of relay, or excessive currents, oxidation or burning from sparking causing high resistance so low currents will heat them up, or other faults which can occur in the relay circuit.

 

An alternator does not produce surplus current. It generates a voltage and tries to maintain that voltage as loads are altered. A battery will not take the excess current, it will charge at x amps dependant on the charging voltage at the battery terminals.

 

Using a voltage sensing relay to operate split charging usually is used to allow the engine battery to recharge 1st. Typically the power taken to start an engine is very small and is under 1Ah of battery capacity. Ancilliary equipment standby power over 24 hours is greater and typical over 24 hours you could have a drain of up to 5 Ah. Not a lot to recharge and so voltage on main battery should rise rapidly and no delay is really exists or is worth worrying about. The advantage of voltage controlled split charge relay is not having to use the D+ output on alternator to control the relay.

 

Most people do not have any problem charging using a standard split charge set up. Those with heavy power use who have problems will still have problems using heavy cables etc. in the time it takes to recharge the batteries. It is also desirabe to have some resistance in the leads supplying the leisure batteries which solves a multitude of other charging related and battery life issues.

 

Going to leave it at that, as really can't be bothered with this anymore and is just turning into an argument.

 

 

 

[Brambles]

Derek Uzzell - 2010-10-25 9:13 AM

 

The voltage-sensing relay referred to by Peter James seems to replicate the ‘coupler/separator’ battery charging arrangement that is the norm for Continental-European-built motorhomes. This has possible technical advantages over the UK-norm split-charge relay set-up, but, if a motorhome has already been fitted with a satisfactory split-charge relay system I really can’t see any genuinely useful gain in messing about with that system to use a voltage-sensing relay instead (or, indeed, vice versa).

 

It's another matter if a vehicle with just a ‘starter battery’ is to be modified to include a ‘leisure battery’ system. Then it clearly makes sense to decide at that point whether the battery-charging arrangement that’s to be installed should be ‘normal’ UK-style or Continental-style, or something more high tech.

 

Timetraveller’s original posting indicates that, despite having 170Ah-worth of leisure batteries and usually only wild-camping for no more than two days, he apparently still finds a need for a generator. This suggests that he is using an awful lot of 12V power during his relatively short off-230V-hook-up stops and/or that the distances driven between the stops are generally so short that the vehicle’s alternator cannot adequately recharge the leisure batteries.

 

Assuming that the SeaScape’s original split-charge relay-based system is functioning properly, I don’t believe a simple voltage-sensing relay alternative will help. Dave Newell’s suggestion of fitting a battery-to-battery charger should optimise leisure-battery charging, but won’t be particularly cheap, neither would opting for ‘free’ charging using solar or wind power.

 

Personally, before considering changing anything, I’d want a) to know what the present charging system is capable of putting into the leisure batteries and b) to analyse how the motorhome is being used and explore whether there’s any easy means of reducing the heavy 12V current drain - for example, replacing filament light bulbs with LED equivalents.

 

Hi Derek, I am wondering if his problem is he only ever does short trips and over a period of time his batteries have lost a lot of charge and so need fully charging. The short 'walk' in the van is only putting in a small amount of charge and so still never getting very high on charge. They may also have detiorated badly as a result, not helping matters.

Maybe the solution to his problem, which we really are only guesssing at, is to plug in his van at home to keep the leisure batteries topped up.

Hopefully you follow what I am trying to suggest.

 

edit - be easier to follow now I have corrected typos.

...and sorry, you have aleady mentioned in your 3rd paragraph...time I shut up and went and did something else.

[Guest Peter James]

Derek Uzzell - 2010-10-25 9:13 AM but, if a motorhome has already been fitted with a satisfactory split-charge relay system.

Well I guessed that his hasn't when he is inquiring about buying a relay. But I could be wrong about that, because he doesn't say?