DC to DC install

Has anyone done a DC to DC install that share their experience (AS Nuevo 2022), unbelievably didn't come with one: 

- Which one 
- Diagram digram 
- Pictures? 
- Do you have to switch of the switch relay on the Sargent unit? 
- Is it relatively easy to do or have you got installer to do it? 

I am think either a Victron or Sargent install. 

Regards,

BOOMEL

I installed the Sargeant DC to DC in our Kingham, after getting the Sargent software up date to switch off the split charge. Mine is a 2021, yours might have the updates, look in the settings on the control panel and see if you have the lithium and the split charge settings. Wiring is fairly straight forward, 2 cables from vehicle battery to the DC to Dc with a fuse at battery end and 2 from the DC to DcC to the leisure battery again with a fuse. If its the sergeant unit it needs a D+ (alternator feed) from the EM40 I have now replaced it with a more powerful Victron unit as I now have a 120 AH lithium battery. I also have the Sargeant DX320-12 for sale.

Tim

I was told that if you fit a BtB to a sargent 328 it causes a loop and flattens starter battery ,is this correct or duff Information .

The problem with the EC328 (and every other EC-series controller, as far as I know) is that it has the split charge function built-in, so you can't just disconnect it without disabling other functions.

I know for sure that it can be done, because Bilbos (the maker of one of our van conversions) still uses the EC328 and has B2B and Lithium battery as an option on all of their vans. Whether that's done via a firmware update to the EC328 I don't know - it's something I keep meaning to find out, but never quite get round to it!

I think the EC700 is the only one to give the split charge off option but only with the latest software. I do remember reading in the MMM magazine that the electrical guru Clive Mott posted a way round it on the earlier EC's

Molly3 wrote:I was told  that if you fit a BtB to a sargent 328 it causes  a loop and flattens starter battery ,is this correct or duff Information .

Not quite correct. The split charge relay in the EC328 connects the starter battery, alternator and leisure batteries together so the B2B that is connected between the starter and leisure batteries reads its output voltage at that of the alternator, thinks its done its job and doesn't charge the leisure battery.

I'm not convinced that that is the full extent of the problem, Peter.

One of the main issues that B2B resolves is the situation where the van is fitted with a smart alternator. In that case, the alternator controller calculates that the starter battery is almost full and reduces its output voltage, long before the leisure battery is fully charged. The leisure battery is typically at the end of a long length of wire on A/S conversions, so it always charges at a lower rate than the starter battery.

When the alternator cuts back its output, you have a situation where the leisure battery is below the voltage at which the B2B charger would say "job done", so the B2B continues to try to raise the voltage on its output (connected to the leisure battery) higher than the voltage on its input (connected to the starter battery). But the output and input are connected together via the split charge relay and a long length of wire...

Quite what happens then is not so easy to predict. It seems obvious that the B2B will go up to its current limiter to start with, but that will place a significant load on the starter battery, so the battery's terminal voltage will start to drop. The alternator will then see that drop and increase its output, bringing the voltage of both the starter and leisure batteries up. The result is that the current flowing thought the B2B should drop, but it's not clear by how much. That would depend on the difference between the threshold voltages in the alternator controller and the B2B. I suspect that the cutoff threshold for a smart alternator in "the starter battery is nearly full" mode will be significantly lower than the B2B's voltage threshold, and so current will continue to flow round the loop - but I don't know, as I've never tested it.

The one good thing though is that this should never be able to flatten the starter battery. The alternator will typically be rated at somewhere between 80A and 120A, which is likely to be higher than most B2B's are rated at, so the B2B won't be able to waste energy (as heat) quicker than the alternator can supply it. But I would think that both will warm up a bit...

Roopert wrote:I'm not convinced that that is the full extent of the problem, Peter.

One of the main issues that B2B resolves is the situation where the van is fitted with a smart alternator. In that case, the alternator controller calculates that the starter battery is almost full and reduces its output voltage, long before the leisure battery is fully charged. The leisure battery is typically at the end of a long length of wire on A/S conversions, so it always charges at a lower rate than the starter battery.

When the alternator cuts back its output, you have a situation where the leisure battery is below the voltage at which the B2B charger would say "job done", so the B2B continues to try to raise the voltage on its output (connected to the leisure battery) higher than the voltage on its input (connected to the starter battery). But the output and input are connected together via the split charge relay and a long length of wire...

Quite what happens then is not so easy to predict. It seems obvious that the B2B will go up to its current limiter to start with, but that will place a significant load on the starter battery, so the battery's terminal voltage will start to drop. The alternator will then see that drop and increase its output, bringing the voltage of both the starter and leisure batteries up. The result is that the current flowing thought the B2B should drop, but it's not clear by how much. That would depend on the difference between the threshold voltages in the alternator controller and the B2B. I suspect that the cutoff threshold for a smart alternator in "the starter battery is nearly full" mode will be significantly lower than the B2B's voltage threshold, and so current will continue to flow round the loop - but I don't know, as I've never tested it.

The one good thing though is that this should never be able to flatten the starter battery. The alternator will typically be rated at somewhere between 80A and 120A, which is likely to be higher than most B2B's are rated at, so the B2B won't be able to waste energy (as heat) quicker than the alternator can supply it. But I would think that both will warm up a bit...

Now I am even more confused!

It was an attempt to explain why you cannot have a split charge circuit operational at the same time as a B2B charger.

To put it more simply, a B2B charger works by raising the voltage of the leisure battery higher than the voltage of the starter battery and alternator. That is (obviously) incompatible with a system that connects those two batteries together.

Roopert wrote:It was an attempt to explain why you cannot have a split charge circuit operational at the same time as a B2B charger.

To put it more simply, a B2B charger works by raising the voltage of the leisure battery higher than the voltage of the starter battery and alternator. That is (obviously) incompatible with a system that connects those two batteries together.

Yes, the B2B takes let us say 12.6 volts from the VB and enhances it to a charging voltage > let us say 13.8 volts, which then charges the leisure battery. But the integral Sargent split charge system simply links the VB & LB battery positive terminals back together, short circuiting the B2B.

If you can switch off the split charge in the software then that is the way to go.

The alternative non-Sargent-invasive solution might be to isolate the LB from the Sargent system when the engine is running. On my van (2019, luckily no smart alternator so not my problem) there is just one little positive cable from the LB + terminal to the EC700. This cable supplies power from the battery (via fuse) to all hab systems, and also conveys the charge from the Sargent split charge system to the LB. I am thinking you could possibly fit a normally closed relay into this cable, switched from the D+, so that when the engine starts that charge/supply cable is cut, thus no short circuit.

The downside is that this will switch off ALL hab electrics since you are powering down the PSU completely. The Sargent normally shuts down most hab electrics anyway when the engine starts, but there may be implications for some things such as the auto step retract and en-route heating. I haven’t thought that part through because as said it is not my problem. My Sargent system is almost completely bypassed at all times in all essential respects (for different reasons) but I do have to leave the EC700 (but not the panel) switched on for the step to retract automatically. I would have thought however that it would make more sense for the step to be wired totally from the VB system but would need to follow some wires and haven’t had the time to address that bit yet.