Split Chargers - B2B & Relays: Which one - or Both?

[wildebus]

oh, I was going to add in a bit of info which I have mentioned before somewhere? CTEK do their D250SE charger and SmartPass optional add-on?
The D250SE is a B2B. the SmartPass is basically a simple relay which is controlled by some logic in the B2B. My Combo setup is essentially like the CTEK combo (but with more control). The reason no other manufacturer has released a pre-packed alternative to the CTEK setup is CTEK have managed to patent it and despite the patent being of dubious validity, the cost of challenging it is beyond the interest of many companies.

 

[wildebus]

I have a BMV700 and would have to insert a relay between it and the rest of the circuit as the BMV700 has only a single contact.

I’m not a massively heavy leisure battery user, albeit we have an inverter powered fridge.

I’m thinking my simplest solution may be to just go with the tr-smart on its own and then see how things work out.

I can always come back to the combined setup if I find I need to.

The only downside I see to this is the loss of the maintenance charge for the vehicle battery. Why I liked this was because the van is our only vehicle and between jaunts away it tends to only get used once a week or so to go to the shop and then that is only a round trip of about 2 miles.

it may be that the alternator voltage is so low because both the leisure and vehicle batteries were already fully charged through the solar.

From what you have said, the B2B is the best solution. You will need to remove the VSR from the setup - but then the easiest way to install the B2B is to just use the same cables from the VSR. You would just chop the connectors off, strip some insualtion and insert into the appropriate connection into the Victron unit. You will have to add a decent cable from the B2B to Ground (the VSR just needs a thin earth cable; a B2B needs a thick cable)

A battery maintainer I think would be worth while. You could also/instead get a little mains battery charger to connect to the starter and give it a periodic full charge. That wouldn't hurt at all I think.

 

[xsilvergs]

Forgot about this little devil, it could be the answer to holding up the starter batteries when the multiplus is turned off.

It seems to work quite well, only charging the SB when the LB is above a certain voltage (programmable).

 

[Nabsim]

My setup was dead easy with the Votronic gear, solar trickle charges 1amp to the starter battery so it’s always getting a top up. B2B just charges hab battery when engine runs, no relays needed. You would think Victron would have realised by now folks are fitting their gear to motorhomes/campers etc and done something about it

 

[wildebus]

My setup was dead easy with the Votronic gear, solar trickle charges 1amp to the starter battery so it’s always getting a top up. B2B just charges hab battery when engine runs, no relays needed. You would think Victron would have realised by now folks are fitting their gear to motorhomes/campers etc and done something about it

The smaller Victron MPPTs (with the load connections) can be configured to provide a charge to the starter battery if you want.
The advantage of a seperate trickle charger is that it will work with any source, so if plugged into EHU you can give the Starter Battery a charge, which is not true of the Dual Solar controllers.
Oh, on that note, if you did use the Victron MPPT controller in the way above, that will charge the Starter when on EHU as well as from Solar.

 

[Nabsim]

Can’t remember what does mine, may be the EBL but when I run the genny I still get a trickle to starter battery. Relay would definitely be cheaper and easier than an EBL if that’s it lol

 

[Phantom]

Just had a good read of this entire great topic and the various ìnteresting ideas to improve charging if the need arises. We're about to fit an Ebocea 1000w PSW inverter in the moho garage where the batteries are and have now decided to use a contactor to connect to mh 240v sockets for convenience, but will pull the oboard battery charger fuse unless on ELH. Going into winter I'm thinking more about alternater charging efficiency really than going overkill on solar, but monitoring it now. We all have different requirements and I'll just adapt the system as needs arise for better efficiency.
I have a device that sends 1.1Ah to the starter battery if it's voltage is 0.5v lower than the leisure batteries, so the starter is always tops first, but have no great worries about drawing some from it.
As said a most interesting and educational topic.

 

[linkshouse]

From what you have said, the B2B is the best solution. You will need to remove the VSR from the setup - but then the easiest way to install the B2B is to just use the same cables from the VSR. You would just chop the connectors off, strip some insualtion and insert into the appropriate connection into the Victron unit. You will have to add a decent cable from the B2B to Ground (the VSR just needs a thin earth cable; a B2B needs a thick cable)

A battery maintainer I think would be worth while. You could also/instead get a little mains battery charger to connect to the starter and give it a periodic full charge. That wouldn't hurt at all I think.

In the end I have kept the VSR (as I have it) and gone with a manual version of your setup. That is, I have fitted a two way switch to select either the VSR or the B2B. Effectively Home/Away. When parked up at home and not getting used much (the van) I can set it to VSR so that the solar such as it is can keep both the LB and VB topped up. When we’re away I can switch it to B2B so the the solar, if there is any, can charge the LB only, and the Alternator can charge both the VB and the LB.

I know it’s not a technical solution but hopefully it will work out for us.

 

[wildebus]

In the end I have kept the VSR (as I have it) and gone with a manual version of your setup. That is, I have fitted a two way switch to select either the VSR or the B2B. Effectively Home/Away. When parked up at home and not getting used much (the van) I can set it to VSR so that the solar such as it is can keep both the LB and VB topped up. When we’re away I can switch it to B2B so the the solar, if there is any, can charge the LB only, and the Alternator can charge both the VB and the LB.

I know it’s not a technical solution but hopefully it will work out for us.

That is a perfectly good option

Whilst I was working out and evaluating options and seeing it there was actually any benefit to doing this (there is little point in doing something just because it can be done if it doesn't also add value) I had the same setup in my Camper ...

Switch between VSR or B2B (Redarc 40A at this time)

Ran this way for quite a while.

 

[Grantls]

Just a comment about the concept of B2B AND VSR in the one install. It works well and and be worth doing IF you have the setup that would benefit. i.e. a big bank that you take down to a fairly low SOC on a regular basis.
As an example, in my camper, sometimes when I plug in, I could be feeding the 645Ah of batteries in excess of 100A for 2 or more hours. In THAT case, a mains charger that only delivers 30A would obviously be over 3 times slower. Transfer that to when driving and if you had an alternator that could deliver 100A+ to the battery it would be much faster than if it went through a 30A B2B instead.
But few alternators can deliver close to 100A in reality (in my camper, it seems to be around 50A max). Plus few batteries (talking Lead Acid now) will take a big charge.

Phil, you talk about the 80% SOC switchover from VSR to B2B. This is something I did using a relay and control from a battery monitor. It is not something that is built into any charger. I just want to make that point as you post some fairly detailed info but didn't mention a battery monitor.
The way you would typically determine the switch over point from a VSR to a B2B is at what SOC the charge current lowers to the max output of the B2B. So you have a 30A B2B installed and a VSR. You find that when using the VSR, the current gradually drops as the batteries fill, and the current hits 30A when the SOC is say 75% (the value will vary from install to install due to different battery setups), then that 75% is around your changeover sweet spot to the B2B. If you had a 60A B2B, the changeover SOC would be lower. The sooner you switch to B2B the better the quality (voltage) of the charge. Before that point you are getting quantity (higher current). You need the charge to be at the right voltage level to complete the charging. This is why VSRs are not the best option to charge a battery as the alternator does not put out a high enough voltage to properly charge a battery (a VSR is not a battery charger, it is just an automated passthrough for the alternator).
The switchover point does also depend on the voltage output of the alternator. If it is pretty low you may need to switch to B2B earlier to get the boost. If the Voltage is around what the batteries like, then switching later is fine.

13.6V sounds remarkably low output? If it is that, then your starter battery will not be getting a decent charge to start with anyway (which could be a different issue you need to manage?) A B2B will work fine setup with the right thresholds but as you say, the VSR will not click on. A battery maintainer such as the AMT would probably be the best match for the B2B.

Really interesting conversation, but I have a couple of numpty questions. Wildebus, you say:

“This is why VSRs are not the best option to charge a battery as the alternator does not put out a high enough voltage to properly charge a battery (a VSR is not a battery charger, it is just an automated passthrough for the alternator).”

My first question is why wouldn’t the alternator fully charge the LB when the VSR is closed (operating as a passthrough) and the alternator is pumping out 14.4v? I would have thought when the VSR is closed both the LB and SB would be in parallel and both batteries should be charging fully?

Second numpty question, why is a DC-DC charger more efficient than a VSR? Are there any real benefits from upgrading the DURITC VSR on my 2007 Citroen Relay (with an old type alternator) to a Victron 30A B2B charger? A bit reluctant to spend £259 on something that makes a minimal difference. Thanks.

 

[wildebus]

Really interesting conversation, but I have a couple of numpty questions. Wildebus, you say:

“This is why VSRs are not the best option to charge a battery as the alternator does not put out a high enough voltage to properly charge a battery (a VSR is not a battery charger, it is just an automated passthrough for the alternator).”

My first question is why wouldn’t the alternator fully charge the LB when the VSR is closed (operating as a passthrough) and the alternator is pumping out 14.4v? I would have thought when the VSR is closed both the LB and SB would be in parallel and both batteries should be charging fully?

Second numpty question, why is a DC-DC charger more efficient than a VSR? Are there any real benefits from upgrading the DURITC VSR on my 2007 Citroen Relay (with an old type alternator) to a Victron 30A B2B charger? A bit reluctant to spend £259 on something that makes a minimal difference. Thanks.

Firstly, have you checked the Voltage output of the Alternator and that it is 14.4V?

Secondly, to properly charge a Lead Acid battery, the charger goes through a certain cycle of constant current with raising voltage (Bulk), constant voltage with decreasing current (Absorption), followed by a float to prevent the battery sitting at too high a voltage for too long.
Your Alternator does none of that.
IF it is putting out 14.4V, and the battery is fully charged already, it will likely be presenting 14.4V all the time a fully charged battery for example.
your Duritc VSR is nothing more than a switch, it is not a charger any more than a piece of cable connecting two cables together is a charger. the only charger in that circuit is the Alternator. And an Alternator is no more a Battery Charger than an old-fashioned Power Supply is a Battery Charger as far as Lead Acid Batteries are concerned. Yes, they put a charge into a battery, but they don't do it in an optimal way to get the most out the battery.
Is it worth spending £259 on a B2B? depends on how much you drive and how well you want to look after your batteries.

 

[Grantls]

Firstly, have you checked the Voltage output of the Alternator and that it is 14.4V?

Secondly, to properly charge a Lead Acid battery, the charger goes through a certain cycle of constant current with raising voltage (Bulk), constant voltage with decreasing current (Absorption), followed by a float to prevent the battery sitting at too high a voltage for too long.
Your Alternator does none of that.
IF it is putting out 14.4V, and the battery is fully charged already, it will likely be presenting 14.4V all the time a fully charged battery for example.
your Duritc VSR is nothing more than a switch, it is not a charger any more than a piece of cable connecting two cables together is a charger. the only charger in that circuit is the Alternator. And an Alternator is no more a Battery Charger than an old-fashioned Power Supply is a Battery Charger as far as Lead Acid Batteries are concerned. Yes, they put a charge into a battery, but they don't do it in an optimal way to get the most out the battery.
Is it worth spending £259 on a B2B? depends on how much you drive and how well you want to look after your batteries.

Yep, the alternator is putting out 14.4V

I've also been doing some further reading on the subject, which supports what you're saying Dave, that by design alternators don't bother to fully charge the starter battery, because it is very seldom a fully charged battery is ever needed to start a vehicle. So a alternator only charges a starter battery to about 80%. So if a lead acid leisure battery is only good for about half it's charge, and the battery is only being charged to 80% by the alternator, you are effectively only able to use about 30% of a leisure battery's charge!

So if you can top up the extra 20% in a battery through a B2B, you actually gain an extra 40% over and above what the alternator will provide you with.

Is any of that making sense?

 

[trevskoda]

An alt puts about 95% at best before decreasing its charging to almost zero even though it shows 14.2 to 14.4, there is a add on unit which tricks them to do the full monty, may have seen the units on ebay some time back, proper smart chargers and solar with a MPPT reg is the way to go, wildbus is the man for all this stuff.

 

[sjak]

Interesting ideas!
I am building my campervan and have been thinking of a way of charging my leisure battery as good as possible with a minimum of cost (don't we all).
So here is my plan:
Combine a dc-dc boost converter ( Granado € 55,-) with a mppt.
Much like you are saying, but without solar panels. In stead of buying a victron orion-tr smart or a votronic.
What are your thoughts?

 

[wildebus]

Interesting ideas!
I am building my campervan and have been thinking of a way of charging my leisure battery as good as possible with a minimum of cost (don't we all).
So here is my plan:
Combine a dc-dc boost converter ( Granado € 55,-) with a mppt.
Much like you are saying, but without solar panels. In stead of buying a victron orion-tr smart or a votronic.
What are your thoughts?

I have not tried this myself, but I see no reason why it should not work, and I believe some folk do operate this kind of setup.

What you are taking about is in many ways similar to some of the Combo B2B/MPPT chargers. It could be worth checking the costs however...

Example:
Victron 100/30 MPPT - to give you 30A Charging ability - Costs around £220
Your DC-DC Converter at £50
Total Cost of hardware = £270

Alternative Option could be the Ablemail AMS 12-12-30 - 30A B2B and a 30A MPPT combined (operates as B2B or MPPT depending on active input) - Costs around £280.

Obviously you can get cheaper than the Victron MPPT, but you can also get cheaper than the Ablemail .... the Ring 30A B2B/MPPT combo is under £200.

Where you plan would be good is if you already have an MPPT knocking around, or if maybe you add a switching relay to an existing MPPTs PV Input and switch between PV Panel and Alternator (using an ignition signal say as an auto-switchover). There is something to be said for not needing to have more than one Smart Charger in an installation and saving that expense.

 

[sjak]

Thanks Wildebus, I might have a mppt that I can use in this setup.
If it still works I only need to get the dc-dc converter.
I'll keep you informed when I have tried it.

 

[xsilvergs]

Interesting ideas!
I am building my campervan and have been thinking of a way of charging my leisure battery as good as possible with a minimum of cost (don't we all).
So here is my plan:
Combine a dc-dc boost converter ( Granado € 55,-) with a mppt.
Much like you are saying, but without solar panels. In stead of buying a victron orion-tr smart or a votronic.
What are your thoughts?

Post in thread 'New Build' https://motorhomebuilder.com/threads/new-build.66905/post-876218

 

[sjak]

Thanks Wildebus, I might have a mppt that I can use in this setup.
If it still works I only need to get the dc-dc converter.
I'll keep you informed when I have tried it.

I have found and tried a pwm, but it doesn't seem to be working.
However I saw a reasonable priced dc-dc charger, a Schaudt wa121525, 25amp., for about £ 100,_ Do you know this brand and is it any good?
,

 

[wildebus]

I have found and tried a pwm, but it doesn't seem to be working.
However I saw a reasonable priced dc-dc charger, a Schaudt wa121525, 25amp., for about £ 100,_ Do you know this brand and is it any good?
,

The Schaudt WA1121525 is what appears to be a very useful booster. I happened to be looking at the setup of one of these for a customer who has one fitted in his brand new Hymer.
There is a good manual here for it which shows how to wire it up for various scenarios - https://www.ivt-hirschau.de/media/920000-Instructions-Booster-WA121545-EN.pdf .
I would think £100 is a pretty decent price for one of these units

 

[sjak]

Thanks Wildebus, I have ordered one in Germany. Total cost including shipping € 140,-.