The B2B question (4 Viewers)

[andy63]

As Andy63 and others recommende

Not me lol.. it was pausims post that put me on to it and I did indeed install one and play about with it before realising that my relays that provided my split charge are external to my cbe power supply unit and are easily disabled without causing any other issues..so I've actually removed the disabling relay on my system now..
Andy

 

[Tombola]

WARNING!

I think i have stumbled upon this "loop" you are talking about. I see the alternator charging indicator for the leasurebattery is going on and off and flickering like crazy. I asume It is because the original split relay switch on when its high enough voltage on startbattery, but when it does, the voltage drops so it turns off again. This happens so fast that i cant measure it. But now i got a whining sound from either the alternator or the turbo. I will find out later, but if it is the alternator its probably because of this.
If thats the case i will name it "The loop of death"

As Andy63 and others recommended, a NC relay is probably the solution on this, but if anybody know how, i would love to just disable the original charging system.

Its this "loop" thats confusing me too. Mine seems to be ok but Id just like to be sure.
as the b2b throws in 30 amps and the alternator with engine running a constant 7-8.5

I measure over a good 10-15 mins and it stays constant 37-38 but after reading all the various posts you have this nagging doubt.

 

[Bore1]

Its this "loop" thats confusing me too. Mine seems to be ok but Id just like to be sure.
as the b2b throws in 30 amps and the alternator with engine running a constant 7-8.5

I measure over a good 10-15 mins and it stays constant 37-38 but after reading all the various posts you have this nagging doubt.

After talking with some b2b and lithium battery dealers i have learned that the original split units are behaving very differently, and wired differently. So if your system looks stable, it probably is ok. When my leisure battery is low the alternator kicks in and deliver 40 amps additional to the 30 amps from b2b.

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[Tombola]

After talking with some b2b and lithium battery dealers i have learned that the original split units are behaving very differently, and wired differently. So if your system looks stable, it probably is ok. When my leisure battery is low the alternator kicks in and deliver 40 amps additional to the 30 amps from b2b.

Yeah you are probably right. My van is a 2019 ducatto and I expected as Euro 6 to be a "smart" alternator, but it isnt. Then reading around I find some MH builders requested non smart from the van manufacturers even after the event so to speak.

 

[Bore1]

Sorry for not giving Pausim the credit.
I cant find any external relay on my unit. I think its internal :/

 

[Pausim]

Sorry for not giving Pausim the credit.
I cant find any external relay on my unit. I think its internal :/

Not a problem. Sorry to hear you are having complications with you installation.

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[andy63]

I cant find any external relay on my unit. I think its internal :/

My system employs two external relays..referred to by chausson as
"Boiler Relays Security " they are the ones responsible for ensuring the alternator charges the leisure battery..
But regardless of where or how your split charge relay or relays are located the charge will be delivered to the leisure batteries via a wire connected to them ..likewise a wire from the start battery will be employed..
So if you connect your battery to battery charger directly between the batteries and not through the power supply board then I think a good place to look at locating a disabling relay would be either in the start battery wire that feeds the split charge circut...or the wire that delivers the charge to the leisure batteries..one of those two wires ..they should be easy to locate as they will be located on either battery..
Just my thinking.. hope you can follow that..
Andy.

 

[andy63]

Me fag packet diag to try and help my explanation..
Regardless of where the split charge relay is located you might still be able to disable it at either of the locations marked in green..

 

[Tombola]

good point andy63 and a clamp metre around the cables will tell you when its carrying current or not

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[Bore1]

Me fag packet diag to try and help my explanation..
Regardless of where the split charge relay is located you might still be able to disable it at either of the locations marked in green..
View attachment 469987

By disabling it,you mean disconnect the wire right? in that case i should disconnect the one from the alternator. If i disconnect the one from leisurebattery i will loose power to the whole system. I remember i saw a relay straped with cable tie to the foot of the truma boiler. i asumed that belong to the truma, but maybe i should have a look again

 

[andy63]

By disabling it,you mean disconnect the wire right?

No.. I ment to put a normally closed relay in to that circut../wire ..that will open on a d+ /engine run signal..so that the circut is just opened when the engine is running..the battery to battery circut will then be the link between the alternator and the leisure battery..
When you shut down the engine the relay closes allowing the original wiring to do its job..like supplying leisure battery power to the board if say you had used the leisure battery side ..( as in me fag packet diag.. )
I should add I'm referring to a system where the split charge circut is part of the power supply unit and not easily accessed..
You are right that if you could access the wiring easily and separately from the power supply board then you could simply disconnect the alternator feed wire..because you have replaced it with the battery to battery charger
Andy

 

[viridiandan]

Hi guys,

On the topic of B2B and/or VSR|SCR -

I've just been dealing with a installing a Renogy 40amp B2B but there's already a Duritc 140amp Voltage Sensitive Relay installed in the van (from the previous owner).

Regarding the issue raised earlier in the thread - of having both devices in place (effectively shorting both positive terminals together and preventing the B2B from putting a load on the cab battery - i.e. the batteries would be charged as before, as if the B2B wasn't even present in the system aka rendering it redundant), my mechanic that was helping me said the following in support of keeping the VSR in place alongside the B2B:

''That (i.e. shorting both positives) would be only if they where wired in parallel. That would essentially negate the resistance that the B2B charger could impart to the circuit. How it's wired in this van is that the voltage sensing relay is acting as a fail safe....

...Consider a potential scenario - your alternator goes into failure mode (ie stops producing more current than the van is using) but the B2B charger will then still be drawing the extra current required to try to charge the auxiliary batteries.
In this case the cab battery would be deplete even faster than it would normally from normal driving....

...The voltage sensing relay would cut off if for any reason the alternator supply voltage drops below 13.1v which is probably not even enough to charge the main vehicle battery, vet alone charge the extra loads. I'd leave it in place. At the moment it's acting as a passive failsafe only.

...Also it's not really the voltage that charges a battery. The voltage only has to be high enough to overcome the internal resistance of the cells. It's all bout pushing in extra electrons, hence current. We measure charging rate in volts only because it's easier. Measuring current would require the ammeter to be in series with the battery, so to connect it you'd have to disconnect the battery, then reconnect it, then test it, then disconnect it to remove the meter, then re-connect it again. So we measure charge rate in volts as if the alternator is unable to produce enough current the voltage would drop proportionally.

...Also just having the voltage sensing relay can act as a straight split charge. As it will only charge the aux batteries when the alternator is charging and/or the supply voltage is above 13.1v. With that system if you where to jump start it from another van it will start to charge the auxiliary system. With the way it is in this van, it'll charge when it has an ignition signal regardless of the charge state in the main battery. Hence a voltage drop relay is an advantage in this scenario.''

Does anyone have any thoughts on this?

Many thanks!

Dan

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[viridiandan]

Hi guys,

On the topic of B2B and/or VSR|SCR -

I've just been dealing with installing a Renogy 40amp B2B but there's already a Duritc 140amp Voltage Sensitive Relay installed in the van (from the previous owner).

Regarding the issue raised earlier in the thread - of having both devices in place (effectively shorting both positive terminals together and preventing the B2B from putting a load on the cab battery - i.e. the batteries would be charged as before, as if the B2B wasn't even present in the system aka rendering it redundant), my mechanic that was helping me said the following in support of keeping the VSR in place alongside the B2B:

''That (i.e. shorting both positives) would be only if they where wired in parallel. That would essentially negate the resistance that the B2B charger could impart to the circuit. How it's wired in this van is that the voltage sensing relay is acting as a fail safe....

...Consider a potential scenario - your alternator goes into failure mode (ie stops producing more current than the van is using) but the B2B charger will then still be drawing the extra current required to try to charge the auxiliary batteries.
In this case the cab battery would be deplete even faster than it would normally from normal driving....

...The voltage sensing relay would cut off if for any reason the alternator supply voltage drops below 13.1v which is probably not even enough to charge the main vehicle battery, vet alone charge the extra loads. I'd leave it in place. At the moment it's acting as a passive failsafe only.

...Also it's not really the voltage that charges a battery. The voltage only has to be high enough to overcome the internal resistance of the cells. It's all bout pushing in extra electrons, hence current. We measure charging rate in volts only because it's easier. Measuring current would require the ammeter to be in series with the battery, so to connect it you'd have to disconnect the battery, then reconnect it, then test it, then disconnect it to remove the meter, then re-connect it again. So we measure charge rate in volts as if the alternator is unable to produce enough current the voltage would drop proportionally.

...Also just having the voltage sensing relay can act as a straight split charge. As it will only charge the aux batteries when the alternator is charging and/or the supply voltage is above 13.1v. With that system if you where to jump start it from another van it will start to charge the auxiliary system. With the way it is in this van, it'll charge when it has an ignition signal regardless of the charge state in the main battery. Hence a voltage drop relay is an advantage in this scenario.''

Does anyone have any thoughts on this?

Many thanks!

Dan

 

[Pausim]

Also it's not really the voltage that charges a battery. The voltage only has to be high enough to overcome the internal resistance of the cells.

I agree that the current does the charging but the direction of flow is dictated by the voltage. If the B2B is raising the voltage supplied to the leisure battery above the level of the engine battery (which is what the B2B is there for) then the current will flow back through the VSR to the engine battery. This in effect means that the 2 batteries are wired in parallel, together with the B2B and alternator. The B2B needs to monitor the state of charge of the leisure battery and the ECU needs to monitor the state of charge of the engine battery. Neither of them can do that properly if everything is parallel connected.

Also just having the voltage sensing relay can act as a straight split charge.

A VSR acting as a split charge relay may work fine if you do not have a smart alternator and if the batteries are of the same type, providing that the wiring is of a sufficient size for a heavy load (often not the case with UK manufactured motorhomes). The Renogy wiring diagram clearly shows separately fused positive connections to the engine battery and the leisure battery, with no VSR linking them.

 

[viridiandan]

Hi Pausim, thanks for that. I'm totally clueless about it all - the copied info was from a mechanic.
What would your advice be in my case? Cheers

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[viridiandan]

PS. Would be super helpful to also hear DBK 's input on this?

 

[Lenny HB]

Also if you have solar and are charging the Starter battery with it you don't want to use a VSR. As when the starter battery rises with the charge the relay will turn on putting the leisure & starter batteries in parallel.

 

[viridiandan]

I do have solar but I'm pretty sure it isn't charging the starter battery.

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[Pausim]

Hi Pausim, thanks for that. I'm totally clueless about it all - the copied info was from a mechanic.
What would your advice be in my case? Cheers

I would disable or remove the VSR and wire the B2B as shown in the instructions, there should also be guidance on what size wires to use.

 

[viridiandan]

Hi Pausim,

Thanks for your replies.

Just to be clear it's a voltage sensitive relay which is situated before the B2B and I don't have a smart alternator.
It's a 2014 Ducato (x250).

The VSR accepts anything from the starter above 13.3v and cuts out at 12.65v.

So if the B2B raises the voltage after this to the leisure batteries, I'm not quite sure how it would flow back to the cab battery in a detrimental way? Also I was under the impression that the B2B itself monitored both batteries (at least that's what I heard about the Renogy).

The leisure batteries are all the same lead acid Hankooks wired in parallel (it's a van conversion).

 

[autorouter]

'That (i.e. shorting both positives) would be only if they where wired in parallel. That would essentially negate the resistance that the B2B charger could impart to the circuit. How it's wired in this van is that the voltage sensing relay is acting as a fail safe....

I think some of the comments were regarding the VSR being in parallel with the B2B. This would in fact have the effect of shorting the B2B positive terminals. The text you quoted is not unambiguous on this point, although on careful reading it seems he is saying that in this setup they are in series, not parallel.

B2Bs and most standard split charge relays are triggered from the D+ signal, which is not the ignition signal. It doesn't go high until the engine has started and the alternator is running.

Many B2Bs, including Sterling, have a voltage-sensitive threshold stage built-in, and the voltage can be adusted or disabled if you want. They also take a D+ input, and the user can decide to use the D+, voltage sensitive, or both.

Measuring current would require the ammeter to be in series with the battery, so to connect it you'd have to disconnect the battery, then reconnect it, then test it, then disconnect it to remove the meter, then re-connect it again.

I don't have much confidence in a mechanic who doesn't seem to have heard of clamp meters or shunts for measuring current, without any of the quoted disconnection problems. It's true that an alternator doesn't measure its output current, but a B2B continuously measures both current and voltage, and uses the measurements to determine the state of charge of the battery. It adjusts its output according to the battery state.

...The voltage sensing relay would cut off if for any reason the alternator supply voltage drops below 13.1v which is probably not even enough to charge the main vehicle battery, vet alone charge the extra loads.

This is exactly what a smart alternator is designed to do - to drop the voltage and stop charging the starter battery in normal running, to leave space in the battery to dump excess energy during braking. MHs with smart alternators need a B2B for this reason.

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[viridiandan]

Thanks a lot for your reply autorouter

I'm pretty sure in my particular setup that they aren't in parallel.

The B2B I have is from the D+

The Renogy has an under-voltage threshold of 8v and over of 16v, as far as I'm aware.

The VSR activates at 13.3v and cuts out at 12.65v.

The same mechanic installed a smart shunt for me so he's well aware of shunts etc.

The vehicle doesn't have a smart alternator.

I'm still unclear if removing the VSR is 100% necessary?

 

[autorouter]

Ensuring that the VSR is not in parallel with the B2B is 100% necessary.

A VSR is not 100% necessary, but there is a case for wiring one in series. It will ensure that charging only happens if the starter battery voltage is higher than the threshold. The D+ signal will ensure that it only charges if the engine is running.

This is relevant in complex systems with solar and mains chargers, plus a battery maintainer trickle-charging the starter battery from the leisure battery. The trickle-charger can raise the starter battery voltage above the VSR threshold, but the D+ will ensure the B2B won't switch on.

The alternator failure scenario is I think a bit unlikely, and not something I would worry too much about. I'd say if you already have a VSR fitted you could incorporate it into the wiring, but if you haven't got one, don't shell out for one.

 

[Raul]

I like the idea of having a vsr in line before the B2B. Can vsr be disabled by a switch?

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[Bore1]

I have given up my VSR. I just diassembled the wire to it so i only use the B2B. Only way i could get a healthy system for the components. With both in place the VSR flippet in and out like crazy, and the alternator flipped up and down from 10 to 90 amps like crazy. And then ofcourse the startbattery would get the same flipping. Can't be good i think.

 

[Pausim]

Hi Pausim,

Thanks for your replies.

Just to be clear it's a voltage sensitive relay which is situated before the B2B and I don't have a smart alternator.
It's a 2014 Ducato (x250).

The VSR accepts anything from the starter above 13.3v and cuts out at 12.65v.

So if the B2B raises the voltage after this to the leisure batteries, I'm not quite sure how it would flow back to the cab battery in a detrimental way? Also I was under the impression that the B2B itself monitored both batteries (at least that's what I heard about the Renogy).

The leisure batteries are all the same lead acid Hankooks wired in parallel (it's a van conversion).

As autorouter said having the VSR and B2B in series does alter matters. The OP’s post was about a CBE DS300 system where the VSR is part of the distribution system and does create a loop by parallel connection if the B2B is directly connected to the batteries. I seem to have misunderstood your post, sorry if this has confused matters.

 

[andy63]

plus a battery maintainer trickle-charging the starter battery from the leisure battery. The trickle-charger can raise the starter battery voltage above the VSR threshold, but the D+ will ensure the B2B won't switch on.

Just adding a little note to that..
I have one of the Stirling 60a battery to battery chargers and it will always default to voltage sensing mode even if supplied with a d+ signal..I'm not sure how common that version is and I know I've mentioned it before ..
So my sterling version of the battery master or start battery maintainer often raised the start battery voltage above the threshold of the battery to battery charger even with the engine off... not a feature i wanted..
I phoned Stirling to see if I could change the battery to battery software as some of their units appeared not to be voltage sensitive if set to a particular mode..
The lad I spoke to at Stirling said the best work around for that in my case was to go to custom settings and change the threshold voltage of the battery to battery charger to a level that prevented it switching on on voltage but it would still react to an engine run signal and switch on..that does appear to have done the trick..and solved that particular issue for me ..
.
On the ds300 boards split charge circuts I think it may be dependant on two factors... the first is the d+ signal and secondly a voltage sensing relay...
Certainly when cbe employ the two large relays which are separate from the ds300 board , that control the split charge , those relays are triggered differently..
One is pure engine run...the other is voltage sensing...
May be of use to someone..
Andy..

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[viridiandan]

Hi guys,

Thanks a lot for your replies and yes I'm conscious of the slight tangent from the original post, but there's very little discussion online on the subject of having both a VSR and B2B installed so I felt this was as good a place as any to further the discussion :

In Renogy's case (40a B2B) it accepts a range from 8v-16v, the lower end of which seems a bit redundant in practice (especially with the VSR installed) as I assume the lowest I'll ever see from the starter (without smart alternator) is around 12v ish?

The VSR situated before it (wired in series, not parallel) accepts any voltage from 13.3v upwards and has a cut-out if it drops to 12.65v so a similar working range seems to be covered (the advantage being the protective 12.65v lower threshold).

I don't see a max voltage threshold anywhere on the VSR so I'm not sure if there would be an issue with the trickle charger increasing the starter to above the max threshold of the VSR?

Waiting to hear back from Renogy re: more confirmation(s).

Cheers,

Dan

 

[autorouter]

Anything connected to an automotive '12V' supply needs to accept a wide range of voltages. 8V is not unusual while starting an engine on a cold day. You don't want it generating panicky error messages every time you start the engine. If you connect the trigger wire to the D+ rather than the ignition then that problem is avoided to some extent, but that's not always possible or convenient.

As you say, the VSR doen't have a max voltage threshold. It will probably have a max voltage limit of maybe 32V, but that's not the issue here. The issue is that the trickle-charger will increase the starter battery voltage to above the VSR turn-on threshold, when the alternator/engine is not running. A mains or solar charger charging the leisure batteries can cause this. Turning on the VSR in those circumstances may or may not be a problem. If the B2B also needs a D+ to fire up, then it's not a problem.

 

[DBK]

PS. Would be super helpful to also hear DBK 's input on this?

I don't really understand what your mechanic is saying. Any relay which connects the positive terminals of leisure and cab batteries together is going to stop the B2B working.

If the alternator fails the B2B won't flatten the cab battery because a B2B only switches on if it either senses a rise in the cab battery voltage (how mine works) or if it detects a voltage at the alternator - the D+ signal.

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