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

[SquirrellCook]

I’m guessing this really about getting the most out of your van on a dull winters day. From what you mentioned before you have more than enough solar power to forget using the engine start battery.

 

[wildebus]

I’m guessing this really about getting the most out of your van on a dull winters day. From what you mentioned before you have more than enough solar power to forget using the engine start battery.

It is really about maximizing the quality of charge from the Alternator when driving, with the last bit about how to automatically get a boost from the Alternator when there is a sudden demand load on the battery.

As an aside I could invoke the Start battery when stationary by closing Relay 1 - which will enable the Cyrix ct-230 AND also close Relay 2, a manual controlled Relay on the Venus GX and which is connected to the Start Assist on the Cyrix. The two together will force the Cyrix on regardless of the voltages.

 

[xsilvergs]

@wildebus

David, that looks very good to me, thanks for taking the time to test this and publish your results.

So, say you have a low SOC on your leisure battery and you start your days travel. The Cyrix carries all the charging current from the alternator, this could be for a reasonable period of time.
Q: What limits the charge current?
Is it the batteries resistance or the alternators output?
If it's the alternator, are you happy with this?

I ask this as I wonder how different battery types (lead, lead-carbon, LiFeP04) would works with this setup.

This saves me counting sheep tonight as I try to get to sleep.

 

[wildebus]

@wildebus

David, that looks very good to me, thanks for taking the time to test this and publish your results.

So, say you have a low SOC on your leisure battery and you start your days travel. The Cyrix carries all the charging current from the alternator, this could be for a reasonable period of time.
Q: What limits the charge current?
Is it the batteries resistance or the alternators output?
If it's the alternator, are you happy with this?

I ask this as I wonder how different battery types (lead, lead-carbon, LiFeP04) would works with this setup.

This saves me counting sheep tonight as I try to get to sleep.

Yup, low SOC and the Cyrix is the Split-Charge device selected.
Generally the limiting factor in most cases would be the Battery Bank.
Usually the alternator will put out more than the battery bank could accept for the majority of motorhomes. In my own case, my battery bank is able to take well over 100A of charge at under 50% SOC (I have tested it at over 140A going in), which is why a 30A B2B would be such a limiting factor. My Alternator I am sure is actually faulty as it maxes out at 45A or so and is something I need to get sorted at some time.

Not used LiFePO4 batteries in this setup, but once I get the Alternator sorted, I might try this as just got a 100Ah LiFePO4 battery.
If you had LiFePO4, you would get the Li version of the Cyrix I would guess. My Batteries are Lead-Carbon AGM and like a lower charge level which is actually fairly ok with a normal Alternator output voltage, but normal AGMs and your own batteries would never charge properly with just a Cyrix ct.

 

[Nabsim]

A question if you don’t mind. I have 2x100ah lifepo4 fitted and I have always had a bigger at the back of my mind that if I started the van with low SOC I could damage the alternator.
Is this unfounded or a real possibility?

mid I get 2 days use without solar I always get genny out to charge before starting engine. Otherwise that would equate to about 130amps to leisure battery’s and whatever needed replacing in starter. I always thought the alternator would charge starter battery before letting anything go to anywhere else in quantity but I guess running cables from starter battery rather than alternator gets round that? Okay that’s two questions lol

 

[wildebus]

2nd one first ... This is a very common misconception that with split-charge systems, the Starter Battery gets charged up and only then the Leisure Battery will get any charge.
There is no reall intelligence like that applied in any commerically installed setup that I am aware off.
On a system that is activated by either the ignition or the D+ (alternator running) signal, as soon as ignition on or engine running, the Leisure Battery is getting a charge from the Alternator (via the Starter Battery +VE terminal) regardless of the charged level of the Starter Battery.
On a system that is activated when the input Voltage reaches a certain level (much more common nowadays), it is possible that the split-charge device (VSR or B2B) will not turn on for a period while the Starter Battery is getting a charge, but it is nowhere near having a full charge first before that happens.

1st one second .... Don't have an answer from my own experience.
I have seen similar concerns about alternators posted on the internet.
Lead Acid batteries cannot take much current anyway so unlikely to be an issue for the great majority of installations of Lead Acid Battery Banks.
Lithium can take a much higher current of course.

I did see this video a while back which I think is worth watching to get some info, but I recall Geeky Phil commenting that (IIRC) the heat issue they are concerned about should not be a factor for most decent alternators? (I think that was the case? Maybe PM Phil for his opinion?)

How far do you let your Lithium Battery Bank discharge to generally

 

[xsilvergs]

Just my thoughts as I follow this post closely.

The alternator fitted to Fiats may (may not) have thermal control which protects itself against failure due to overheating as per the video.
Now imagine the day when your Leisure battery is discharged to its lowest SOC. It's cold and your Starter battery manages to start the engine but only just. Phew.

Case 1: So the alternator is now powering headlights, engine electrics, etc, etc, and trying to charge those batteries, will the alternator have charged the starter battery enough for the next start in 5 minutes time? Can it do all this? After a period of time its output could be reduced through thermal management, now how much current can it pump out?

Case 2: A 60 Amp B2B working flat out to charge the Leisure batteries will only take a max ~ 60 Amps, leaving up to 90 Amps of alternator output to charge the Starter battery and run the engine electrics. If the van can't use the 90 Amps available the alternator should run cooler prolonging its life. A LiFePo4 Leisure battery could receive 180 Ah in a 3 hour drive, that should be enough.

Just a thought, the alternator is rated 150 Amps, but did the manufacturer in an attempt to save weight use a large enough wire gauge to carry 150 Amps for the next 3 hours? That wire could be bundled in a loom where it may have little cooling, so we now have a heater and a volt drop.

Personally I'm for a B2B until somebody convinces me otherwise.
As I say, just my thoughts.

 

[wildebus]

The cable to the battery in a Ducato that has the battery under the passenger footwell looks realtively small?
Where the battery is in the Engine Bay, the cable from Alternator to Battery I would think would be shorter so maybe typically more capable?


If the battery is so low it only just started the engine AND the lights and other vehicle electrical equipment is on, there is a fair chance the VSR OR the B2B will not be energised as the voltage will be too low with all the vehicle demand to be high enough to enable the B2B - and if it raises enough to turn on a split-charge device and the Leisure Battery starts to pull a high current, the voltage will likely drop and cause the device to turn off again.

This might help illustrate that above situation ....

RED_LB-V&C-Ext by David, on Flickr
The Redarc B2B in this example is rated higher than the "Alternator" (actually a mains charger connected to the Starter Battery, but the principle is the same)., so tries to get more current than the Vehicle 12V system can provide.
And after a while the Vehicle side cannot keep up and the voltage drops, turning the B2B off. The Starter Batter recovers, voltage increases and the B2B turns on, and the cycle repeats over and over. The voltage trend does increase as there is more power going into the system then is being used, but that trend depends how much excess power there is.

Note the voltage shown above is the LEISURE Battery. The Starter Battery voltage (which is the voltage that is turning on the B2B) is a lot lower and you can see it jumping up and down to above and then below the B2B on/off thresholds

RED_SB-Voltage by David, on Flickr


It is not that unusual for a van alternator to fail shortly after the installation of a split-charge unit (happened a couple of times to me) as the extra load put on it was like the last straw for a failing unit. Not really an issue with the extra load but a bad alternator and when the owner got it repaired/replaced, the problem was fixed.
As I mentioned, my own vans alternator won't put out more than around 45A, so the 60A B2B I fitted to try out kept switching down to half-power 30A - as whenever it tried to pull the full 60A, the alternators voltage dropped and so half the B2B shut off. Nothing to blame other than the 17 year old alternator which is meant to be a 90A unit I think.
So even a B2B could just mask a failing unit.

 

[xsilvergs]

Small cable! equals reduction in warranty claims for failed alternators, good ploy.

Nice to see graphs, one day David we'll find something you don't have a graph for ;-) .

Good point regards low voltage dropout of VSR/B2B.

 

[Nabsim]

I have only let my lithium go below 80% once and that was when I only had the one battery. With the two if we aren’t getting enough sun and not moving I aim to keep them above 40% generally simply for the amount of time to recharge, sooner run genny an hour or two each day than all day as I don’t like to leave it running when not there.

I can’t help wondering why manufacturers don’t fit second alternators to take care of charging banks of battery’s. Is this easy to do, I assume not in general as not seen posts where it’s done but not investigated.

@xsilvergs your scenario is why I went with a B2B rather than fitting a proper split charge system, my factory split charge wasn’t effective enough to cause a problem.

 

[Deleted member 4404]

I have only let my lithium go below 80% once and that was when I only had the one battery. With the two if we aren’t getting enough sun and not moving I aim to keep them above 40% generally simply for the amount of time to recharge, sooner run genny an hour or two each day than all day as I don’t like to leave it running when not there.

I can’t help wondering why manufacturers don’t fit second alternators to take care of charging banks of battery’s. Is this easy to do, I assume not in general as not seen posts where it’s done but not investigated.

@xsilvergs your scenario is why I went with a B2B rather than fitting a proper split charge system, my factory split charge wasn’t effective enough to cause a problem.

Common practice on boats, but there is usually more space around the engine

 

[xsilvergs]

I have only let my lithium go below 80% once and that was when I only had the one battery. With the two if we aren’t getting enough sun and not moving I aim to keep them above 40% generally simply for the amount of time to recharge, sooner run genny an hour or two each day than all day as I don’t like to leave it running when not there.

I can’t help wondering why manufacturers don’t fit second alternators to take care of charging banks of battery’s. Is this easy to do, I assume not in general as not seen posts where it’s done but not investigated.

@xsilvergs your scenario is why I went with a B2B rather than fitting a proper split charge system, my factory split charge wasn’t effective enough to cause a problem.

We have a Nordelettronica controller, although it works OK I have noticed that the Solar can charger the Leisure battery to 100% and that on starting the engine the Leisure battery discharges a few percent into to the slightly depleted Starter battery. Obviously the SCR in the Nordelettronica controller isn't intelligent.

 

[SquirrellCook]

Have any of you considered the energy used (fuel burnt) in using your engine to charge batteries? I've been thinking along the lines of, if you could drive your alternator you could use surplus solar to help the engine? Or at the very least keep your engine start batter fully charged so the alternator just free wheels?

 

[wildebus]

Have any of you considered the energy used (fuel burnt) in using your engine to charge batteries? I've been thinking along the lines of, if you could drive your alternator you could use surplus solar to help the engine? Or at the very least keep your engine start batter fully charged so the alternator just free wheels?

Indeed so. The greater the output demanded from the Alternator, the greater the load on the engine and the higher the fuel burnt.
I think TBH that goes without saying? And why things like electric fans where introduced decades ago?

I would be amazed if there are any base vehicles used commercially for motorhomes that would let you reverse-feed with any effect the power from the "leisure systems" to help save fuel when driving.
The nearest setup I have seen in off-the-shelf methods to notionally save fuel that is with the Redarc BCDC Dual B2B/MPPT Unit, where the B2B and MPPT will operate at the same time. Most Combo units are one or other and will revert to Alternator Charging when the engine is running - the Redarc Dual unit though will have both active and have the MPPT input as priority and only use the alternator side to top up the difference between what the Solar is providing and what the Leisure Battery is wanting.
I wonder how much fuel is actually saved though by cutting 10 or 20A off the Alternator output? I bet very little in comparision to the fuel used to run/drive the engine.
You can do something along similar lines also by having your B2B charger set at a lower voltage than your MPPT controller. Then the B2B will see a fully-charged battery earlier and start to reduce its demand and even go into float mode while the MPPT is still working away normally.
Of course having some kind of battery maintainer/connection where surplus solar will keep the starter battery fully charged when idle could have knock-on future benefit so once the vehicle is started, the alternator won't need to do as much starter battery charging.


But I don't think we will see any bi-directional type power sharing unless you have a fully-electric driven vehicle - and even then I would doubt it would happen. But it would be good to have some kind of "holistic" (think that would be the term?) overall system setup to make the most of all sources in the whole vehicle
You could maybe have the Alternator connected with a Magnetic Clutch, like Air Con Compressors use to engage when needed? but would the cost of that much more expensive alternator be prohibitive for the limited benefit as what percentage of vehicles have excess Leisure Side power to send to the Engine side anyway?

 

[wildebus]

Thought I would do a little update on this ....

I had initially tried this B2B/VSR Combo using an Ablemail B2B and the way I tried it involved some additional hi-power relays and some extra heavy-duty cabling, so it worked but was really not ideal.
The Victron has a remote control input for both L and H (low voltage control and high voltage control - you chose how you control it) and that was ideal for this B2B - VSR Combo right out the box

But I decided to revist the Ablemail B2B as I was sure this should be possible in a much easier way - and it was!
You can reprogramme the Ablemail B2B unit (well, the supplier can, the end user cannot usually) to use the Voltage sensing input essentially as a remote control feature.
It can only be controlled by a high voltage signal (unlike the Victron), but the control signal for the VSR must be low voltage, so a slight issue. But this can be overcome by just using a simple low-current relay costing a couple of quid and simple wiring, and not involving any current-carrying cable, so now I can use the Ablemail charger (which I believe is actually better (it has a higher output for sure) than the Victron Orion-tr Smart B2B) in a dual B2B-VSR setup by a tweak to the wiring which cost under £2 and took a couple of minutes to fit

 

[xsilvergs]

Thought I would do a little update on this ....

I had initially tried this B2B/VSR Combo using an Ablemail B2B and the way I tried it involved some additional hi-power relays and some extra heavy-duty cabling, so it worked but was really not ideal.
The Victron has a remote control input for both L and H (low voltage control and high voltage control - you chose how you control it) and that was ideal for this B2B - VSR Combo right out the box

But I decided to revist the Ablemail B2B as I was sure this should be possible in a much easier way - and it was!
You can reprogramme the Ablemail B2B unit (well, the supplier can, the end user cannot usually) to use the Voltage sensing input essentially as a remote control feature.
It can only be controlled by a high voltage signal (unlike the Victron), but the control signal for the VSR must be low voltage, so a slight issue. But this can be overcome by just using a simple low-current relay costing a couple of quid and simple wiring, and not involving any current-carrying cable, so now I can use the Ablemail charger (which I believe is actually better (it has a higher output for sure) than the Victron Orion-tr Smart B2B) in a dual B2B-VSR setup by a tweak to the wiring which cost under £2 and took a couple of minutes to fit

I see a circuit diagram coming .

Great to see somebody who thinks outside the box and then has a go. As one who was always told "you can't do that" it made me more determined.
Love it.

 

[wildebus]

I see a circuit diagram coming .

Great to see somebody who thinks outside the box and then has a go. As one who was always told "you can't do that" it made me more determined.
Love it.

I will append my current Victron diagram to suit the Ablemail and post it . FWIW, the same design will, I think, also work with the Redarc BCDC Controller.

As an aside, I think I have found why the 60A model didn't run at full speed always ... the OFF-Voltage was set a bit too high to suit my aged Alternator. After making an adjustment, it is working much more as expected

 

[wildebus]

I see a circuit diagram coming .

Here you go ....

This involves an little extra relay compared to the Victron. But this does add a little extra flexibility as well. On the BMV, you have a built in relay with an NO (Normally Open) and a NC (Normally Connected) output. If your control device only has a simple on/off (open/closed) rather then this dual output, then an extra relay would be needed anyway.
In the wiring above I have shown it as it could be used by the CCGX as well as the Venus GX or BMV (the CCGX only has a NO output).
When the Relays NO is open (relay off), the output (which would otherwise would 0ve) is open, so the VSR cannot operate, and the extra relay is off. This means pin 30 and pin 87a are connected and the B2B is allowed to operate.
When the Relays NO is closed (relay on), the output is 0ve, the VSR has its ground so can operate, and the extra relay is also on. This means Pin 30 is connected to Pin 87 and Pin 87a is open - meaning the Voltage sense connection to the B2B is floating and the B2B cannot operate.
(I could use the Relays NC connection and use Pin 87 instead of 87a instead if using the BMV or a Venus GX, but there is actually an advantage to not doing so - using NO only and Pin 87a means that the relay is typically off and not drawing any power when the control switch/Relay is off. A tiny saving power, but still a saving )

For the Ablemail, you need to chose a specific setting in the Ablemail AMC 30-12-12 (highlighted below within the various selections - the Run Control Input setting).

 

[SquirrellCook]

So am I correct to say that the Orion-Tr Smart DC-DC would work as well?

 

[wildebus]

So am I correct to say that the Orion-Tr Smart DC-DC would work as well?

Well, yes. As per this post earlier.