Mastervolt Magic DC-DC Converter - what is it and why do I need it?

[picardy]

An electrical system designer is suggesting a Mastervolt Magic 12/12-20 DC-DC converter for my new install.

Despite asking him to explain it I am still unsure what it does or why it is needed! I will have a 20hp Yanmar with 2 batteries running fridge, bilge, shower pump etc. I was expecting to see a VSR but this hasn't been specified.

1. What is DC-DC converter and why is it needed for a fairly small boat
2. Does it replace a VSR or should I have one of those too?
3. Would you recommend one?

Many thanks

 

[KompetentKrew]

Magic 12/12-20 | Mastervolt

It does indeed seem like it could replace a VSR, but it's not clear to me why you'd prefer it to a DC-DC charger.

 

[William_H]

I would agree with OP that a VSR would seem to be a simple reliable solution to isolation/charging of a services battery. The mastervolt device might work well as a battery to battery charger. Set up to only charge when engine is running. The advantage is that you could get a higher charge voltage from the engine alternator system to accelerate charge into services battery. So more charge for less engine running time. An alternator charge controller could also do this. ie get the alternator to produce 15 volts instead of 14v.
So unless you want max charge into service battery. ie if you find you are running the engine just to charge batteries , then a VSR with less charge current might suit you.
ol'will

 

[PaulRainbow]

An electrical system designer is suggesting a Mastervolt Magic 12/12-20 DC-DC converter for my new install.

Despite asking him to explain it I am still unsure what it does or why it is needed! I will have a 20hp Yanmar with 2 batteries running fridge, bilge, shower pump etc. I was expecting to see a VSR but this hasn't been specified.

1. What is DC-DC converter and why is it needed for a fairly small boat
2. Does it replace a VSR or should I have one of those too?
3. Would you recommend one?

Many thanks

Do you have the system design ?

Is the converter just being used to charge one battery from another ?

For the very brief system description you give, it seems an expensive option, but more information is really needed.

 

[Stemar]

For the very brief system description you give, it seems an expensive option,

My nasty suspicious mind is wondering if your designer hasn't got one he wants to shift.

It could be useful if you've got a 20v DC laptop you want to use on board, but otherwise, I really can't see what it would do that a £30 VSR wouldn't do.

 

[VicS]

An electrical system designer is suggesting a Mastervolt Magic 12/12-20 DC-DC converter for my new install.
Despite asking him to explain it I am still unsure what it does or why it is needed! I will have a 20hp Yanmar with 2 batteries running fridge, bilge, shower pump etc. I was expecting to see a VSR but this hasn't been specified.
1. What is DC-DC converter and why is it needed for a fairly small boat
2. Does it replace a VSR or should I have one of those too?
3. Would you recommend one?
Many thanks

1. It is a device that can take a DC input and covert it to a DC output at another voltage. The Mastervolt Magic will function as a multistage battery charger powered from the DC system .

Its impossible to say why it has been suggested for your boat without full details of your electrical system including physical layout, cable run lengths etc.​

​

2. It will replace a VSR,

You will not need one as well, at least not for charging the same battery that the DC-DC converter is charging.​

3. If the second battery is located close to the primary battery probably not.

A VSR should be adequate , but as already said one needs to know full details of your electrical system​

​

Post the reasons the electrical engineer has given for suggesting the DC-DC converter.

 

[picardy]

Very helpful advice as ever. I will challenge on the use of the Magic system instead of a BEP or similar VSR.

Many thanks everyone

 

[picardy]

Thanks again all. As requested I am uploading the schematic. Thoughts on whether a VSR would be sufficient instead of the Mastervolt Magic would be appreciated. The batteries will be in the bow of the boat and the Engine and Safety Hub 150 will be midships (3m from the batteries approx).

I am only running the 1st fix cabling as the boat is built - an electrician will make final connections but I always like to get advice from this forum as I go.

The engine cables have not been shown on here but I am told that I will need to run 3 pairs of 35mm battery cables as follows

1 pair for the engine starter motor
1 pair for the alternator charging (as shown on here)
1 pair for the domestic supply (as shown on here)

Is that right or does the alternator and the engine starter share the same cable?

Thanks in advnace

 

[PaulRainbow]

Mains and alternator charging both go to the domestic battery and the DC-DC charger charges the engine battery, so slightly different to a VSR.

There will be a 35mm negative cable going to the engine block or starter, depending on whether it's isolated return or not. If it goes to the block, the alternator does not need an additional negative cable, if it's isolated return, a short 25mm cable from the starter connection to the alternator negative terminal should be fine.

A short 25mm cable from the B+ terminal on the alternator to the starter positive would be fine to charge the engine battery, which would be fine with a VSR, but the DC-DC charger won't charge the domestic batteries. If all charging was connected to the engine battery and the DC-DC converter was wired the other way around it would work and save running the extra cables, but it seems pointless fitting the DC-DC charger like this, the point of the design is to give the engine battery a different charging regime to the domestic battery. From the information given, i'd question the need for doing this though.

IMO, two options:

Stick with the design.

Fit a VSR rather than the DC-DC charger. Use the starter cables for charging the engine battery. Leave the mains charger as it is.

I'm afraid i'd have to question the wisdom of paying a professional to design the system and then seek opinions from an internet forum.

 

[masterofnone]

I happen to have a brand new sterling ProAlt C 80a alternator to battery charger. I intended to install but changed alternator instead. Retail £382 .80, sensible offers please.

 

[pvb]

I happen to have a brand new sterling ProAlt C 80a alternator to battery charger. I intended to install but changed alternator instead. Retail £382 .80, sensible offers please.

I don't think you have a sensible idea of the real retail price. Cactus sell it for £275, for example.

 

[PaulRainbow]

I happen to have a brand new sterling ProAlt C 80a alternator to battery charger. I intended to install but changed alternator instead. Retail £382 .80, sensible offers please.

Of no relevance to this thread, the OP has a 120a alternator, for one thing. Perhaps you'd be better off posting in the for sale forum, but you'll need to put a price.