FITTING A VSR (instead of a split-charging diode)

[Bubble32]

I noticed yesterday whilst cruising under engine that the Model 702 ‘Multi-Battery Isolator’ on my 2003 Bavaria 32 with a MD2020D engine gets quite hot when the engine is running. This demonstrates clearly what is well-known – these split-charging diodes waste a lot of power. I’m on a round-Britain cruise at the moment so maintaining the batteries is a major issue for me. The owner of the boat I am cruising in company with, a Westerly, has replaced his diode with a VSR and I have seen his installation. It must be possible to replicate on my B32.

However, I have looked up the installation instructions for the VSR (https://allbatterysalesandservice.com/information/Instructions/SurePower/Marine_Isolators.pdf) and they say: “Be sure that the alternator has remote sense capability. Most single-wire Delco alternators do not have this provision”. I don’t understand this and I don’t know whether or not the original alternator on the MD2020D does in fact have that capability.

Any advice?

Many thanks, Jonathan (www.yachtbubble.com)

[Yngmar]

The normal way to install a VSR is to leave the alternator directly connected to the engine battery, always charging that one as is intended. Therefore there are no problems with alternator sensing, no matter whether it senses at the battery or at the alternator.

The VSR then, upon detecting a suitable charging voltage, will switch on, connecting the house bank to the alternator (and starter battery) and charging both. This can optionally be combined with a smart regulator (e.g. Maxcharge).

At least that's how it works on our boat and has been working well for many years now, apart from the VSR having died once in that time. I have replaced it with a Victron Cyrix-CT one and can recommend that.

[Keweetoo]

I have a Blue Sea ACR fitted same way as Yngmar - alternator connected to engine start battery and the ACR linking start and house batteries. This works well and providing there is a charging current the two banks are linked, and separated if no charging current detected. No need for alternator remote sensor and does not loose about 1V in charge current a traditional isolating diode will.

[tiger79]

However, I have looked up the installation instructions for the VSR (https://allbatterysalesandservice.com/information/Instructions/SurePower/Marine_Isolators.pdf) and they say: “Be sure that the alternator has remote sense capability. Most single-wire Delco alternators do not have this provision”. I don’t understand this and I don’t know whether or not the original alternator on the MD2020D does in fact have that capability.

The instructions you've linked to are for diode splitters - not VSRs.

The modern alternative to "old style" diode splitters is the low-loss splitter.  My Bavaria was fitted from new with a Quick ECS low-loss splitter.  This has virtually no voltage drop, and consequently doesn't waste power generating heat.  One advantage over a VSR is that you can get 3-output low-loss splitters, enabling you to charge the start, house and thruster batteries independently.

https://www.quickitaly.com/en/products/energy-range/charge-separator/ecs/

If you'd prefer to fit a VSR, the Victon Cyrix-ct which Yngmar suggested is a good quality, lower cost choice.

[Clivert]

You can, of course, revert to the manual system that we had on our Moody. A three way manual switch that allowed us to switch to starter on engine start, then switch to all when the engine  was running, and the to house or service batteries when sailing.
it was pretty fool proof.
 

[symphony2]

Not as fool proof as 2 completely separate banks and a split charging system which needs no intervention to ensure that both banks are properly charged. You can then (as Bavaria and all other builders do) have a small battery dedicated to the engine and use the space to have a large house bank. No danger of running the notional engine start flat by forgetting to switch away from it when using it for house loads. The Moody system dates back to the 1970s when boats first started to need electricity and it was a short cut to add another battery and use both for all purposes. Now the demands of the house bank are wat above the engine so require a different kind of setup.

[tiger79]

You can, of course, revert to the manual system that we had on our Moody. A three way manual switch that allowed us to switch to starter on engine start, then switch to all when the engine  was running, and the to house or service batteries when sailing.
it was pretty fool proof.

But not totally foolproof, which is why the RNLI is kept busy towing in boats which can't start their engines!