# Split Charge Relay



## bigclick (Oct 9, 2011)

Hi all,

We have a Hymer b544 1997

Is there a built in split charge relay in this vehicle?

Is it any good, can it be replaced with a stand-alone unit?

How would the SCR impact if I was to wire in a B2B charger?


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## boringfrog (Sep 22, 2006)

I would think there would be a built in relay.


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## WildThingsKev (Dec 29, 2009)

The best way to integrate a b2b charger is to put a (normally closed) relay between the SCR (which may well be part of a 12v distribution panel) and the leisure batteries. This relay is opened by a signal from your "engine running" or "D+" signal wire (the one used to switch the fridge to 12v), this will isolate the leisure batteries from the domestic 12v system when the engine is running. Your b2b charger is now connected directly between the vehicle and leisure batteries and will efficiently charge the LBs as intended without any conflicting voltages.

About to do this next week myself.

Kev

ps. on my installation this relay will also knock out charge from the solar panel whilst the engine is running.


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## Pudsey_Bear (Sep 25, 2008)

WildThingsKev said:


> The best way to integrate a b2b charger is to put a (normally closed) relay between the SCR (which may well be part of a 12v distribution panel) and the leisure batteries. This relay is opened by a signal from your "engine running" or "D+" signal wire (the one used to switch the fridge to 12v), this will isolate the leisure batteries from the domestic 12v system when the engine is running. Your b2b charger is now connected directly between the vehicle and leisure batteries and will efficiently charge the LBs as intended without any conflicting voltages.
> 
> About to do this next week myself.
> 
> ...


My system uses the Smartcom to trigger a 200a HD relay, for the LBs and a 30a relay for the fridge, the LBs stay attached to the solar panel.

Why do you need to isolate the Solar input, as the Smartcom will sense when the LBs are fully charged anyway won't it, shut down that circuit and continue to power the fridge.

Not 100% sure, so a question not an argument.

Sorry to take it off topic, but it is related to the OPs query.


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## WildThingsKev (Dec 29, 2009)

I thought I'd edited the last line to say I need to look at that again; I roughly planned this 3 months ago but am just getting around to doing it.

My solar currently goes through the Rapido 12v system so as it stands will also be disconnected when the relay opens. Therefore I either need to reroute it (I have the preinstalled Rapido wires available) or add a relay (operated by "ignition on") to isolate the panel from the regulator.


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## Pudsey_Bear (Sep 25, 2008)

WildThingsKev said:


> EDITED add a relay (operated by "ignition on") to isolate the panel from the regulator.


I understand what you're doing, but why isolate the solar panel at all?


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## bigclick (Oct 9, 2011)

The B2B device i was looking at actually has a separate terminal just for the solar panel

I am still not sure where to connect things in, I will have another read but thanks again for the advice


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## WildThingsKev (Dec 29, 2009)

Kev_n_Liz said:


> WildThingsKev said:
> 
> 
> > EDITED add a relay (operated by "ignition on") to isolate the panel from the regulator.
> ...


A B2B charger will give the optimum 3 stage charging cycle when there are no external voltages/charging on the leisure batteries, whether from a SCR or solar reg. It has a separate sensing wire to accurately measure the battery voltage. I realise that most chargers (240v, solar, b2b) are probably installed on top of one another and work adequately but if I'm spending £300 on a sophisticated bit of kit I want to give it the best chance to work 100%.

The last bit about isolating the panel from the solar reg is because the reg is going to be disconnected from the batteries and therefore needs to reconnect to them before it reconnects with the panel (for initiating itself).

Hope that makes sense, my solar reg is not a 3 stage one so would put a constant 14.1v on the LBs.

Kev


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## WildThingsKev (Dec 29, 2009)

bigclick said:


> The B2B device i was looking at actually has a separate terminal just for the solar panel
> 
> I am still not sure where to connect things in, I will have another read but thanks again for the advice


Is that the ctek d250s? There are a few threads about which way to best connect it; here and here.

I considered that one but decided I wanted a bit more oomph because we will be spending January and February in the Alps skiing. In the end I bought a German made 45A Votronic b2b charger which is designed for motorhomes rather than a Sterling one which is designed for marine use. They are however very similar in performance and specification.

Votronic b2b charger


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## Pudsey_Bear (Sep 25, 2008)

Thanks KEv, I don't understand it but that more to do with my grey cells than your explanation.

To me it seems so far over the top, but each to their own methods, my wallet doesn't allow such things.

Surely the panels charge while it's sunny including when driving, the VSR/Smartcom charges when I drive, don't both shut down once the battery is fully charged, the only benefit seems to be the VB is charged too when on solar only, but Clive Motts single wire solution takes care of that too.

If that's wrong OK, as I'm a dummy when it comes to the way all this lot works together


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## WildThingsKev (Dec 29, 2009)

The standard Rapido SCR system together with an 80W panel has been fine for normal touring but the last two winters skiing have just about killed off our Banner Energy Bulls. Investing in the b2b charger is to make the most of and look after our expensive new Victron gel batteries.

Isolating solar for a couple of hours whilst driving around mountains in January, even on a sunny day, is only going to lose a few Amp hours. Meanwhile the b2b will be putting in 45Ah.


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## Pudsey_Bear (Sep 25, 2008)

WildThingsKev said:


> The standard Rapido SCR system together with an 80W panel has been fine for normal touring but the last two winters skiing have just about killed off our Banner Energy Bulls. Investing in the b2b charger is to make the most of and look after our expensive new Victron gel batteries.
> 
> Isolating solar for a couple of hours whilst driving around mountains in January, even on a sunny day, is only going to lose a few Amp hours. Meanwhile the b2b will be putting in 45Ah.


I wish I was clever like you Brian


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## WildThingsKev (Dec 29, 2009)

Getting your head around someone else's electrical system is probably the most difficult thing on this forum, especially once modifications (or selfbuilds) are introduced.


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## Pudsey_Bear (Sep 25, 2008)

WildThingsKev said:


> Getting your head around someone else's electrical system is probably the most difficult thing on this forum, especially once modifications (or selfbuilds) are introduced.


Even if you did your own it's hard to remember exactly what's where.


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## bigclick (Oct 9, 2011)

WildThingsKev said:


> bigclick said:
> 
> 
> > The B2B device i was looking at actually has a separate terminal just for the solar panel
> ...


Yes it was the ctek from an outfit called RoadPro?

Thanks for the links


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