Split charge relay stays made because of solar panel voltage?

[AllanK]

I have installed a split charge relay in order to allow charging of the leisure batteries from the alternator and also to allow the fridge to operate from 12v when on the move. The relay closes at about 13.5 volts.
This works ok except that the voltage from the solar panel (at 14 or so) prevents the voltage sensing relay from dropping out when the engine stops. This is obviously because the voltage sensing connection is still too high when the relay is made -- a catch 22 situation. Can anyone suggest a circuit or device that would overcome the problem which must be quite common?

 

[Steve and Denise]

How about a relay before the solar reg to disconnect the solar while the engine is running take a signal from fridge + or alt

 

[tonyidle]

If the sensing relay stays operated as you suggest then you have sufficient solar power going spare. Leave it as it is.

 

[Gromett]

If the sensing relay stays operated as you suggest then you have sufficient solar power going spare. Leave it as it is.

Wouldn't that run the risk of burning out the relay if the van is then started while active?

PS: I don't know, I have never used one so don't know how they operate.

 

[pappajohn]

Dump the voltage sensing relay and fit a regular 30amp automotive relay which is triggered by the alternator D wire. (ignition switch controlled)
Ignition off, no D signal from alternator so relay opens.

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[AllanK]

Some excellent advice here my favourite being from tonyidle . I should have added that the relay does eventually drop out after a short time and I realise now that the fridge, if left on battery , pulls the voltage down and the relay will break before any harm is done. Also the idea from pappajohn is a good one except that it would mean running another wire all the way from front to back of the vehicle. The idea from steveand denise is a good one and I already have an intermediate relay switching the fridge so I might change this for a two pole one and route the solar input through it. Many thanks to all for some quick and sound advice

 

[pappajohn]

the idea from pappajohn is a good one except that it would mean running another wire all the way from front to back of the vehicle

I don't understand why.
You already have a wire from the engine bay to the hab battery via the volt sense relay, you don't need another.

A short wire from alternator D to the relay in the engine bay then a short wire to earth to complete that trigger circuit.
A short wire from the engine battery to the relay then your existing charge wire to the relay to complete the split chsrge circuit.

 

[Lenny HB]

Dump the voltage sensing relay and fit a regular 30amp automotive relay which is triggered by the alternator D wire. (ignition switch controlled)
Ignition off, no D signal from alternator so relay opens.

Totally agree also if it's a cheap voltage sensing relay made for the towing market they are far to unreliable for use in a Motorhome.

Also far more sensible to fit separate relays for fridge and battery charging.

 

[tonyidle]

Wouldn't that run the risk of burning out the relay if the van is then started while active?

PS: I don't know, I have never used one so don't know how they operate.

No - it's simply looking at its power source (the starter battery) to determine whether it's OK to charge the leisure battery and power the fridge. Although we still call it a split-charge relay and think of it as something to do with the alternator it is actually a simple voltage sensing device. Whenever start battery voltage passes a trigger level (whether that is caused by the alternator or any other source) the sensing relay simply connects the start battery to the leisure battery to charge it and to the fridge. As soon as start battery voltage drops below a preset threshold (normally because the engine is turned off so the alternator ceases to charge) the relay will release the connection. Your solar is simply mimicking the alternator. The split charge relay doesn't care.

 

[AllanK]

I have only one wire running from the engine bay (battery +) to the rear of the vehicle which is a very heavy cable that was originally fitted to power a wheelchair lift when it was a disabled bus. All of my motorhome electrics are at the rear so what I am trying to do is make use of this cable by sensing the voltage on it and switching the fridge and leisure batteries in when it rises and out when it falls. (around 13.6 /12.6 respectively) It's true that my voltage sensing relay a "TEC3M" is a cheapie made for caravans. There are better looking ones out there such as Durite but they don't seem to have an output for the fridge? To see what I mean about the layout take a look here -https://goo.gl/photos/zdmezNNkXTCstwHe6

Sorry but the link above doesn't seem to work. Try this instead --

https://photos.google.com/share/AF1...?key=TWVyVU1LMHRLYTZFaHJJcTVHNzYxTVFTbWVEOVRB

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[AllanK]

Sorry but the link above doesn't seem to work. Try this instead --

https://photos.google.com/share/AF1...?key=TWVyVU1LMHRLYTZFaHJJcTVHNzYxTVFTbWVEOVRB

 

[Lenny HB]

As you already have a power feed cable at the back of the van to use conventional split charge relays you only need to run a small signal cable to the back of the van to switch the relays.

 

[tonyidle]

As you already have a power feed cable at the back of the van to use conventional split charge relays you only need to run a small signal cable to the back of the van to switch the relays.

I don't really understand why a decent voltage sensing relay is considered a poorer option than the relatively old-fashioned approach you suggest? Most motorhomes use voltage sensing within their control units for this purpose. If I'm wrong & the unit you have proves to be unreliable then at that time you can replace it with something more robust or go the D+ route.

 

[Gromett]

No - it's simply looking at its power source (the starter battery) to determine whether it's OK to charge the leisure battery and power the fridge. Although we still call it a split-charge relay and think of it as something to do with the alternator it is actually a simple voltage sensing device. Whenever start battery voltage passes a trigger level (whether that is caused by the alternator or any other source) the sensing relay simply connects the start battery to the leisure battery to charge it and to the fridge. As soon as start battery voltage drops below a preset threshold (normally because the engine is turned off so the alternator ceases to charge) the relay will release the connection. Your solar is simply mimicking the alternator. The split charge relay doesn't care.

I understand that. However..... Think about this, normally when you switch the engine off this relay opens disconnecting the vehicle from the hab area.
So when you start the engine and draw a huge amount of current this will not be pulled from the leisure battery.
The difference in voltage between the alternator output and the leisure batteries will not usually be very much 14.1V for the alternators and say 12.4v for the leisure battery around 1.4V So the current flow will be be relatively low and the cable and relay are specced for this.

Now imagine this relay is now connected when you start the engine. A huge current flow is taken from the battery which pulls the voltage down to quite low levels. I have seen mine go down to as low as 9v on cranking. The leisure battery is at say 12.7v (fully charged) 12.7v - 9v - 3.7 volt which is a big jump from the 1.8v The starter is happily guzzling all these electrons and doesn't care where they come from. So it will pull through the relay, through that wire that is not specced for the job and cause either a fuse to blow or the wire to melt?

Unless the relay is clever with over current protection then I can see this being an issue theoretically?

As I said. I have never even looked at a split charge relay. But my understanding is that they are only supposed to connect the two batteries together when the alternator is running and the cab battery is up to a certain voltage. It then effectively parallels the two batteries for charging from the alternator.

 

[AllanK]

As you already have a power feed cable at the back of the van to use conventional split charge relays you only need to run a small signal cable to the back of the van to switch the relays.

Thats true but its such a pain threading wires through out of sight.

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[AllanK]

I understand that. However..... Think about this, normally when you switch the engine off this relay opens disconnecting the vehicle from the hab area.
So when you start the engine and draw a huge amount of current this will not be pulled from the leisure battery.
The difference in voltage between the alternator output and the leisure batteries will not usually be very much 14.1V for the alternators and say 12.4v for the leisure battery around 1.4V So the current flow will be be relatively low and the cable and relay are specced for this.

Now imagine this relay is now connected when you start the engine. A huge current flow is taken from the battery which pulls the voltage down to quite low levels. I have seen mine go down to as low as 9v on cranking. The leisure battery is at say 12.7v (fully charged) 12.7v - 9v - 3.7 volt which is a big jump from the 1.8v The starter is happily guzzling all these electrons and doesn't care where they come from. So it will pull through the relay, through that wire that is not specced for the job and cause either a fuse to blow or the wire to melt?

Unless the relay is clever with over current protection then I can see this being an issue theoretically?

As I said. I have never even looked at a split charge relay. But my understanding is that they are only supposed to connect the two batteries together when the alternator is running and the cab battery is up to a certain voltage. It then effectively parallels the two batteries for charging from the alternator.

You're quite right but my problem is that the scr doesn't know when to let go due to the solar voltage being high.

 

[Gromett]

You're quite right but my problem is that the scr doesn't know when to let go due to the solar voltage being high.

That's what I was originally responding to. @tonyidle didn't think it would be a problem. I think it might be.. Sorry I can't help with a solution as I have no knowledge of how they are plumbed in etc.

 

[mitzimad]

Thats true but its such a pain threading wires through out of sight.

run it under the van

 

[mitzimad]

ive heard of this problem before my self build used a smartcom relay to trigger a dumb relay no d plus needed i was told vsr's compare voltage either side where as the smart com senses rise on one side only thus not affected by the solar and theres a fridge connection on the smartcom

 

[Lenny HB]

I don't really understand why a decent voltage sensing relay is considered a poorer option than the relatively old-fashioned approach you suggest? Most motorhomes use voltage sensing within their control units for this purpose. If I'm wrong & the unit you have proves to be unreliable then at that time you can replace it with something more robust or go the D+ route.

I did say cheap ones made for the tugging use were unreliable.

Thats true but its such a pain threading wires through out of sight.

Not a pain it's. challenge.

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[AllanK]

ive heard of this problem before my self build used a smartcom relay to trigger a dumb relay no d plus needed i was told vsr's compare voltage either side where as the smart com senses rise on one side only thus not affected by the solar and theres a fridge connection on the smartcom

I've looked at the Smartcom and I'm sure it's the same thing as the TEC3M that I am using in all but name. It's identical.

 

[AllanK]

I've looked at the Smartcom and I'm sure it's the same thing as the TEC3M that I am using in all but name. It's identical.

It does sense voltage on one side only buy the problem is that once the relay is made the voltage is the same on either side until it breaks.

 

[tonyidle]

I understand that. However..... Think about this, normally when you switch the engine off this relay opens disconnecting the vehicle from the hab area.
So when you start the engine and draw a huge amount of current this will not be pulled from the leisure battery.
The difference in voltage between the alternator output and the leisure batteries will not usually be very much 14.1V for the alternators and say 12.4v for the leisure battery around 1.4V So the current flow will be be relatively low and the cable and relay are specced for this.

Now imagine this relay is now connected when you start the engine. A huge current flow is taken from the battery which pulls the voltage down to quite low levels. I have seen mine go down to as low as 9v on cranking. The leisure battery is at say 12.7v (fully charged) 12.7v - 9v - 3.7 volt which is a big jump from the 1.8v The starter is happily guzzling all these electrons and doesn't care where they come from. So it will pull through the relay, through that wire that is not specced for the job and cause either a fuse to blow or the wire to melt?

Unless the relay is clever with over current protection then I can see this being an issue theoretically?

As I said. I have never even looked at a split charge relay. But my understanding is that they are only supposed to connect the two batteries together when the alternator is running and the cab battery is up to a certain voltage. It then effectively parallels the two batteries for charging from the alternator.

No the unit will switch off when the starter battery is pulled down by the starter. What you're suggesting could happen to any mh that used voltage sensing: a stop and restart of the engine could do the same aa you suggest.

 

[Gromett]

No the unit will switch off when the starter battery is pulled down by the starter. What you're suggesting could happen to any mh that used voltage sensing: a stop and restart of the engine could do the same aa you suggest.

As I said I don't know how these things works...

 

[AllanK]

Totally agree also if it's a cheap voltage sensing relay made for the towing market they are far to unreliable for use in a Motorhome.

Also far more sensible to fit separate relays for fridge and battery charging.

Yes, actually I have fitted seperate relays for the fridge and battery charging.

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[mitzimad]

For what they cost why not try my way use the smartcom to feed the fridge fit a new relay between the two batteries and trigger that from the smartcom the dumb relay is the only outlay and it worked for me
I was also rd the smartcom didn't last so carried a spare for five years and was going strongwhen I sold it as it was only used as trigger and fridge relay it didn't see high current

 

[JIXAMAN]

I know this is a dead thread but...

I have converted a 2013 Mercedes Sprinter NCV and installed a Cargo split charge relay. I also have a 160w solar with an MTTP controller going into a 270ah battery, all 37 kilos of it. All good...

Well, no. Twice on sunny days here in the UK and every time we stopped in daytime in Europe this year the van was dead.

When I say dead, it had power, I could lock and unlock it, the battery had plenty power but the key (an electronic fob that acts as a key) although could go into the slot would not activate the van in any way shape or form, not even to unlock the electronic steering lock. It is an over voltage protection I now know.

I thought it was heat related as only happened on hot days but after doing it at mid day after only a short run and being dead till late evening I came to the conclusion it was split charge / solar related. Its been disconnected for two months now and no issues so investigation almost over.

Today I am going to reattach the relay and I found this thread while researching a solution.

Although its an old thread I registered on the forum just to reply as although there are some good answers, it looks like no one has experience with the same problem and that it needed a definitive as the only answer that would help someone such as myself (OP too maybe) was to use power from the leisure battery (fridge was mentioned) but as said was untested as no one had similar issue.

In light of this, I think a battery cutoff switch is the answer to the problem, installed on the leisure battery side of the relay and mounted on the seat base where the cable passes through to the rear. Switch off and the starter battery will go below the threshold and will allow the relay to drop out.

Hope this helps.

 

[autorouter]

Is the MPPT controller functioning correctly? It would be an idea to actually measure the starter battery voltage directly on its terminals with a multimeter to get an accurate reading of the voltage. Also check that the controller is set for the correct battery type (not AGM or Gel) if there is a choice.

I'm not sure on this, but I'd be surprised if the overvoltage protection is triggered by normal charging voltages.

 

[JIXAMAN]

No, defo is the case. When it was doing it in Germany I tested voltage and it was like 14.something and disconnecting the leisure battery fixed it right away.

Settings are ok on controller, theres a cause for the relay staying open and it's only evident when in bright sunlight and the charge voltage is high...

As said, I'll put the switch in and report back...

Cheers...

 

[HandyAndy]

Now imagine this relay is now connected when you start the engine. A huge current flow is taken from the battery which pulls the voltage down to quite low levels. I have seen mine go down to as low as 9v on cranking. The leisure battery is at say 12.7v (fully charged) 12.7v - 9v - 3.7 volt which is a big jump from the 1.8v The starter is happily guzzling all these electrons and doesn't care where they come from. So it will pull through the relay, through that wire that is not specced for the job and cause either a fuse to blow or the wire to melt?

Nope...
As soon as you turn the ign on before you even crank the engine, voltage will drop below the setpoint of the sens relay due to the amount of ancillaries go live and it will disconnect.

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