other split charge system

I can't help but hopefully someone will be along soon. (y)
 
You could do but it's terribly inefficient to use two transformers 12v - 240v - 12v

Can you not wire up the batteries in series with an isolating switch when not driving so the habitation battery dosen't drain the engine battery

I'm new to this game so take it with a pinch of salt!

Cheers James
 
inva said:
so if i got a 12v - 230v inverter that plugs into the cigarette socket in the dash, then plugged into the inverter a 230v-12v battery charger, is this an
alternate split charge system


https://rover.ebay.com/rover/1/710-...0001&campid=5338547443&icep_item=383582059125

https://rover.ebay.com/rover/1/710-...0001&campid=5338547443&icep_item=283541259591
Click to expand...
what are you trying to achieve presumably to charge a leisure battery but what do you want to run off it, you dont need a 230v charger to charge it

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chatteris said:
what are you trying to achieve presumably to charge a leisure battery but what do you want to run off it, you dont need a 230v charger to charge it
Click to expand...
i want a split charge system i dont have to wire up
 
This unit will charge the leisure battery at 7A using a standard auxiliary 120w cigarette lighter sockett. Good luck
2020_07_01_05.01.13.jpg
 
inva said:
i want a split charge system i dont have to wire up
Click to expand...
You can’t have one lol

The inverter is only 200w so the battery charger wouldn’t work any way

Even If it did, taking 12 VDC up to 230v AC then converting it back down to 12 VDC is extremely inefficient so your battery wouldn’t charge

As pappajohn suggested a 30 amp automotive relay will do the job

If you want to try that ask and I’ll post a simple diagram for you if your not sure how to do it

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Heavy cable and a battery idolator switch would do the job as well as giving you a built in jump start system
with certain caveats .
 
tacr2man said:
Heavy cable and a battery idolator switch would do the job as well as giving you a built in jump start system
with certain caveats .
Click to expand...
did that to my mates sprinter race van only needed short bits of cable and isolater mounted through side of passenger seat box he just turns it on when he travels anywhere and off when he gets there,
 
inva said:
but which wires do i need and where do they go
Click to expand...
Please see below....

3E2487AD-ACFC-4522-BBB2-5A600DB4EB5A.jpeg

basically the voltage sensing split change relay bridges the positive between the two batteries and has a small ground of its own.
 
Not only will it work in principle (I didn't follow the links to see if the devices themselves are suitable), but it will provide a significantly more effective solution than a split charge relay. This is because the smart charger will be able to apply a much more effective charging regimen than a split charge relay, which will lose volts over the connecting cable and charge very slowly. It is basically what a B2B charger does internally, possibly not to 230V, but it can definitely boost voltage over the supply voltage. Your solution will be less efficient electrically than a custom designed B2B device, but who cares, because that 12V with the engine running is pretty cheap. The key would be to ensure that the smart charger was matched to the inverter and both had sufficient duty cycle for the task. I'd go for a 10A smart charger over a 30A relay any day of the week, as the 30A relay is just a maximum current before it burns out. It doesn't mean that 30A will actually flow, just that it won't blow up until it does. It'll do little more than a highish trickle charge unless the batteries are mounted close to each other with large cables to reduce resistance and it will have no protection against overcharge (vehicle alternators usually push out constant high voltage to ensure good initial charge, but this is bad once the battery is full), especially for more fragile batteries like gels etc.

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cmcardle75 said:
Not only will it work in principle (I didn't follow the links to see if the devices themselves are suitable), but it will provide a significantly more effective solution than a split charge relay. This is because the smart charger will be able to apply a much more effective charging regimen than a split charge relay, which will lose volts over the connecting cable and charge very slowly. It is basically what a B2B charger does internally, possibly not to 230V, but it can definitely boost voltage over the supply voltage. Your solution will be less efficient electrically than a custom designed B2B device, but who cares, because that 12V with the engine running is pretty cheap. The key would be to ensure that the smart charger was matched to the inverter and both had sufficient duty cycle for the task. I'd go for a 10A smart charger over a 30A relay any day of the week, as the 30A relay is just a maximum current before it burns out. It doesn't mean that 30A will actually flow, just that it won't blow up until it does. It'll do little more than a highish trickle charge unless the batteries are mounted close to each other with large cables to reduce resistance and it will have no protection against overcharge (vehicle alternators usually push out constant high voltage to ensure good initial charge, but this is bad once the battery is full), especially for more fragile batteries like gels etc.
Click to expand...
You should follow the links

You cannot run a decent mains charger through a cigarette socket inverter

Its daft and silly and will not work

Which is why no manufacturer has ever done it
 
I concede it's daft and no manufacturer would do it because no-one wants wires hanging out of their dashboard (and certainly not from a commercial motorhome supplier) and some lighter sockets are limited to 10A (although he mentioned a 200W inverter that would hopefully imply a 20A outlet). However, despite this, it definitely would work and be more effective than a split charge relay.

Much better would be a dedicated B2B charger, which would be very similar internally in design to the combined electronics described. As in there would be a switch mode power supply capable of providing the target battery with a higher voltage than the source battery, both to provide optimum power transfer, provide battery conditioning and to overcome losses in the cables. By putting these units in one box, you get the opportunity to do the power transfer only once (not via an intermediary voltage) and be a bit more efficient, but these supplies are typically pretty efficient anyway. If they're not, they tend to melt!
 
cmcardle75 said:
I concede it's daft and no manufacturer would do it because no-one wants wires hanging out of their dashboard (and certainly not from a commercial motorhome supplier) and some lighter sockets are limited to 10A (although he mentioned a 200W inverter that would hopefully imply a 20A outlet). However, despite this, it definitely would work and be more effective than a split charge relay.
Click to expand...
No it wouldn’t

You simply cannot run a inverter through a cigar lighter socket, to power a battery charger that would actually efficiently charge a leisure battery.

The reason that Cigar lighters are rated at 120w (10amp) is more than that they get hot and melt

The inverter will be crap, but that aside lets say it’s 80% efficient. The battery charger “claims” 85% efficiency, so there is a huge loss straight away.

Simple physics tells us you can’t get more out than you put in.
 
No-one's claiming that you get out more than you put in. Or that if there is only a 10A outlet, then you're going to struggle. However, even with a 15A outlet (which is pretty common) and only 50% overall efficiency whilst flat out (I suspect it would be better than this), you could still run a 7.5A output smart charger. With a remote battery location (i.e. not sitting next to the engine battery) and the typical 4/6mm cable run, this may provide a higher charge current than a split charge relay, especially once the habitation battery is no longer deeply discharged and no longer providing a substantial potential difference across the long cable run. This is even more so with a smart alternator which may sense the vehicle battery filling up and reduce the output voltage and will stop charging the habitation battery altogether.

I suspect the biggest issue with making it actually work is the quality and duty cycle of the inverter, which would probably burn out with this sort of continuous use, rather than the occasional use it was designed for.

BTW, I do have a degree in electronic engineering and as part of this we were required to design and construct our own DC to DC voltage multiplying switched mode power supplies.

So I'm not saying it is a good idea. However, there is nothing in simple physics that would prevent it working. Of course, you're better off with a dedicated battery to battery charger (such as this linked one). Split charge relays are pretty lame and don't even work on modern (i.e. Euro 6) vehicles with smart alternators.

<Broken link removed>
 
cmcardle75 said:
No-one's claiming that you get out more than you put in. Or that if there is only a 10A outlet, then you're going to struggle. However, even with a 15A outlet (which is pretty common) and only 50% overall efficiency whilst flat out (I suspect it would be better than this), you could still run a 7.5A output smart charger. With a remote battery location (i.e. not sitting next to the engine battery) and the typical 4/6mm cable run, this may provide a higher charge current than a split charge relay, especially once the habitation battery is no longer deeply discharged and no longer providing a substantial potential difference across the long cable run. This is even more so with a smart alternator which may sense the vehicle battery filling up and reduce the output voltage and will stop charging the habitation battery altogether.

I suspect the biggest issue with making it actually work is the quality and duty cycle of the inverter, which would probably burn out with this sort of continuous use, rather than the occasional use it was designed for.

BTW, I do have a degree in electronic engineering and as part of this we were required to design and construct our own DC to DC voltage multiplying switched mode power supplies.

So I'm not saying it is a good idea. However, there is nothing in simple physics that would prevent it working. Of course, you're better off with a dedicated battery to battery charger (such as this linked one). Split charge relays are pretty lame and don't even work on modern (i.e. Euro 6) vehicles with smart alternators.

<Broken link removed>
Click to expand...
:doh:

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Having installed hundreds of Battery to Battery chargers and spent 30 years playing with the optimum ways to do things, I put this together to explain the differences of charging regimes

Easy for me as I just wander around the stock room and take pictures of all of the different things that we use

 
eddievanbitz said:
:doh:
Click to expand...

You can smack your head all you like, but it would work! (At least until the cheap inverter burnt out, anyway!)

If you think it won't work you'll need to come up with a reason why. Don't think I'm suggesting this as an actual solution. I'd go for a proper B2B charger any day of the week!
 
cmcardle75 said:
You can smack your head all you like, but it would work! (At least until the cheap inverter burnt out, anyway!)

If you think it won't work you'll need to come up with a reason why. Don't think I'm suggesting this as an actual solution. I'd go for a proper B2B charger any day of the week!
Click to expand...
OK so you agree it is stupid and is grossly inefficient! And here are some reasons as requested

cmcardle75 said:
No-one's claiming that you get out more than you put in. Or that if there is only a 10A outlet, then you're going to struggle. However, even with a 15A outlet (which is pretty common)
Click to expand...
"Pretty Common" Not on Ford, Fiat or Mercedes So hardly "pretty common"

So you now have to find a mains charger that will work off of a 120w inverter!

cmcardle75 said:
50% overall efficiency whilst flat out (I suspect it would be better than this), you could still run a 7.5A output smart charger. With a remote battery location (i.e. not sitting next to the engine battery) and the typical 4/6mm cable run, this may provide a higher charge current than a split charge relay,
Click to expand...

Absolute Tosh!

1593687334498.png

This split charge relay is rated at 140 amp, connected with the correct cable it will be infinitely better than a pony mains charger running off of a 120w inverter. I wouldn't use one, but it would be better than running a 120w inverter

cmcardle75 said:
I suspect the biggest issue with making it actually work is the quality and duty cycle of the inverter, which would probably burn out with this sort of continuous use, rather than the occasional use it was designed for.
Click to expand...
So your expecting it to burn out as it isn't intended for the use you suggest?

cmcardle75 said:
BTW, I do have a degree in electronic engineering and as part of this we were required to design and construct our own DC to DC voltage multiplying switched mode power supplies.
Click to expand...
When can we see this in production? Mine is called a Battery Master (y) available at all good motorhome specialists and online.

cmcardle75 said:
So I'm not saying it is a good idea.
Click to expand...
Which is what we have been telling the OP to avoid him buying the stuff that won't work, and as your Electronics Degree training has suggested will "burn out"


cmcardle75 said:
However, there is nothing in simple physics that would prevent it working.
Click to expand...

Except of course the 15 -20 amp rated 12 volt sockets just don't exist, the thing is very likely to burn out, a cheap VSR relay would beat the output of ANY 230 VAC charger with only 120W input

But I would concede that you could buy the charger and the inverter and plug it is and "turn it on" it would "work"

You keep missing the word "efficiently"
 
So we are now agreed that it would work, but be a fairly stupid idea? Previously, it was against the laws of physics!

However, we don't agree that a VSR relay would work efficiently with a large cable run. You could have a million amp relay and it won't make any more current flow, especially with a smart alternator (like many/most vehicles built in the last ten years) that will crank down the volts to trickle charge when the car battery is full.

However, this would be better for your business as you can sell decent battery to battery chargers that actually work at a much greater profit than VSR relays, which only work on old vehicles with constant voltage alternators with unnecessarily large cables and/or batteries mounted close together.

TBH, I had trouble getting enough charge current from two adjacent batteries with 16mm cable with a split charge relay. A CTEK 250 sorted that out!
 
Hi you need / want one similar to this MOTOR HOME SELF SWITCHING, VOLTAGE SENSING SPLIT CHARGE RELAY KIT - 12V, 30 AMP..... Copy and paste on eBay £27 kit

Subscribers  do not see these advertisements

 
cmcardle75 said:
So we are now agreed that it would work, but be a fairly stupid idea? Previously, it was against the laws of physics!

However, we don't agree that a VSR relay would work efficiently with a large cable run. You could have a million amp relay and it won't make any more current flow, especially with a smart alternator (like many/most vehicles built in the last ten years) that will crank down the volts to trickle charge when the car battery is full.

However, this would be better for your business as you can sell decent battery to battery chargers that actually work at a much greater profit than VSR relays, which only work on old vehicles with constant voltage alternators with unnecessarily large cables and/or batteries mounted close together.

TBH, I had trouble getting enough charge current from two adjacent batteries with 16mm cable with a split charge relay. A CTEK 250 sorted that out!
Click to expand...
And where did I say it was against the laws of physics?

Perhaps you misread this "Simple physics tells us you can’t get more out than you put in" which I did say, in this post
You simply cannot run a inverter through a cigar lighter socket, to power a battery charger that would actually efficiently charge a leisure battery.

The reason that Cigar lighters are rated at 120w (10amp) is more than that they get hot and melt

The inverter will be crap, but that aside lets say it’s 80% efficient. The battery charger “claims” 85% efficiency, so there is a huge loss straight away.

Simple physics tells us you can’t get more out than you put in.
Click to expand...

I didn't say it wouldn't work, I said as you can see was with 120w you cannot efficiently charge a leisure battery.

Regarding your set up 25mm2 would have been much better

Regarding B2B systems we install loads of them, have done for years.
 
Terry said:
Hi you need / want one similar to this MOTOR HOME SELF SWITCHING, VOLTAGE SENSING SPLIT CHARGE RELAY KIT - 12V, 30 AMP..... Copy and paste on eBay £27 kit
Click to expand...
thanks for replies. cant see the link terry
 
its easier to just plug something into the dash
 

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