Solar Panel connection question

[Loafer]

Dear Lectrickery Geezers (or ladies)

 

Is there any reason why I can't connect the output from an MPPT controller (which should be connected to the battery bank) to a B+ on one of my alternators?

 

The advantages would be great. Each alternator has 'f-off' cable to the batteries and would save me about 2m of awkward cabling. Plus I'd see the solar panel delivery current on one of my alternator ammeters, without having to peer at a tiny LCD screen.

 

I'm guessing the minuscule volt drop across the ammeter shunt would be negligible.

 

Anyone? A virtual beer for the best reason why. Or why not. Any BSS snags that you can see?

 

PS the panel controller will be programmed to give 14.8V max, so should keep going even when the alternator B+ has it's own 14.4V or so. All cabling is well capable of carrying the alternator's 90A max, plus the 200W panel max current of about 14A.

 

Apologies in advance if this is posted in the wrong place. I'm fitting them tomorrow and am hoping for this to be seen early.

 

Ta.

[Paul C]

In theory all connection points for current into and out of the battery bank should meet at one place, but in practice what you want to do, sounds okay. You need to have an inline fuse in between the MPPT controller's output and wherever its connected. For some strange reason, the alternator B+ to battery +ve is exempt from being fused (according to BSS regs), and so is a battery +ve connection to starter motor, but they're the only two which are exempt.

[Loafer]

In theory all connection points for current into and out of the battery bank should meet at one place, but in practice what you want to do, sounds okay. You need to have an inline fuse in between the MPPT controller's output and wherever its connected. For some strange reason, the alternator B+ to battery +ve is exempt from being fused (according to BSS regs), and so is a battery +ve connection to starter motor, but they're the only two which are exempt.

Good point, the fuse. Will add that, thanks.

 

Contender for the virtual beer!

[Ark Right]

For some strange reason, the alternator B+ to battery +ve is exempt from being fused (according to BSS regs), and so is a battery +ve connection to starter motor, but they're the only two which are exempt.

Correct me if I'm wrong, isn't it the case that the exemption applies only because they each go through a main isolator switch.

Which is often overlooked, particularly the isolator to the secondary (house or domestic bank) alternator.

Direct connection I believe requires a fuse. No isolator is bad practice to say the least.

A

[by'eck]

Removed

Edited January 31, 2014 by by'eck

[Detling]

Battery to starter is exempt because the cranking current for a cold diesel will destroy most available isolators, When I designed a test rig for starter motors the stall current we had to cope with could exceed 1000 amps not may isolators will take that and not melt.

[ditchcrawler]

Battery to starter is exempt because the cranking current for a cold diesel will destroy most available isolators, When I designed a test rig for starter motors the stall current we had to cope with could exceed 1000 amps not may isolators will take that and not melt.

Mine has lasted 12 years so maybe 1500-2000 starts

[mango]

Battery to starter is exempt because the cranking current for a cold diesel will destroy most available isolators, When I designed a test rig for starter motors the stall current we had to cope with could exceed 1000 amps not may isolators will take that and not melt.

I don't recall seeing any boats without an isolator in the starter circuit. With a decently maintained engine the cranking time is short and I have never encountered a damaged isolator.

[by'eck]

I don't recall seeing any boats without an isolator in the starter circuit. With a decently maintained engine the cranking time is short and I have never encountered a damaged isolator.

 

Agreed, I have this BEP one for the starter battery:

 

Continuous Duty Rating: 275 amperes.

 

Intermittent Rating: 455 amperes.

 

Maximum Intermittent Duty Rating: 1250 amperes for 15 seconds.

 

This isn't even the heavy duty version which has the following spec:

 

Rating: 600 amps (continuous) / 2500 amps (intermittent cranking).