Electric ala Rube Goldberg

Phil, details you requested:

Solar panels are 12V each, one per battery, connected through a toggle switch so I can cut 'em out for winter layup.

The ship still has her original-equipment separate 12V house system, including two Group 31 house batteries. No starting battery of course. Standard Perko A/B/Both/Neither switch. For logistics' sake these batteries are the same model as the propulsion batteries, so that if one of the important ones craps out, I can swap one of the house batteries in. I even have a loose one for the electric outboard on the dinghy.

Generator energizes the shore power cord. (I mean, I simply plug the 30-foot long yellow cable into the Honda.)

The shore power can energize any of:
1: 72VDC charger (switched via a timer)
2: original equipment 12 VDC charger (switchable on both sides)
3: original equipment below-decks 120 VAC bus (outlets in head, galley, and dinette. Two original-equipment circuit breakers.)

Alternatively, I can energize the below-decks 120 VAC outlets via a little 300 W inverter energized from the 12VDC bus.

The 12VDC bus draws from the house batteries, but there is a switchable interconnect via a 72:12 DCC converter, that has the effect of giving me a 10 kWh house bank.

In practice, the switches are set so that the 12V bank is tied to the 72V bank, and the below-decks AC is supplied by the little inverter. The shore power is only used to charge the 72V batteries. But I'll admit that if we hit a marina w/ power for a night after a few weeks on the hook, we'll plug in and charge the laptops, phones, house bank, and even the electric toothbrush!

72V side is fused at 200 Amps (fuse, not a circuit breaker.) Normal steaming current is ~40 Amps. WOT is ~150 Amps.

Tranny is flanged to the shaft - no belt. (In rev 0 if the systems I had the motor belted to the tranny, but the motor bearings aren't really intended to carry that much side load.

Best regards,

Chris

 

Phil: The following description of control switches may be informative:

6x Solar panel in/out

Inverter On / Off
72:12 On / Off
12V Charger On / Off
72V Charger On / Off (Timer)

120 VAC source: Shore Power / OFF / Inverter
12 VDC Source: Charger / OFF / 72:12

WARNING: Panel is energized from multiple sources.

 

Tie down strap: Yes, certainly a good idea. We just did a project for a disabled sailing association that has the battery for the assistive systems simply sliding around in a compartment under the helm seat. They were sure free to move "more than one inch" in several directions, including vertically!

 

Perfect, thanks.

There was a point to all this, really there was. Remember this from earlier -

Notice that in cmcK's system, there isn't any free sharing of capacity between a 72Vdc distribution and the 12Vdc house system. It is actually cheaper to have two independent systems than to piggyback the house, or integrate the house. So what seemed like a real good idea doesn't really come to fruition. It would cost about $1000 to have an automatic, never have to think about it, 72 to 12 Vdc piggyback system. It would cost about $500 to use a good grade class A 72 to 12 Vdc converter and manual monitoring and switching with some dedicated 12V house batteries. You can buy an el cheapo downconverter for $35. If I had a pair of el cheapos, I'd use jumper cables and sit there watching them while connected. Then put them back in a waterproof box. Some people would be perfectly happy doing this as needed for 20 years, but it can only be considered an owner-operator kludge. Don't expect your gf to do it.

 

Good discussion. Even if it meanders (philSweet's observation), it's all still useful to me.

As a beginner, I'll ask cmckesson what will likely seem a silly question:

What is the purpose of a mixed voltage system (12VDC and 72VDC)?

Any particular reason that you chose that specific battery?

Thanks.

 

Happy to respond: The 12V side exists because the normal ship's electrics are 12V powered: VHF radio, lighting, etc.

One would not choose to run propulsion at that low a voltage because the amperage would be very high: 5 kW at 12V is about 400 Amps, which means things get hot.

In effect what I have is one large battery bank, from which I can take 72VDC, 12VDC, or even 120VAC, according to need.

Oh, why the Group 31 Trojans: First aspect of this question might be "why Lead-Acid?" That answer is easy: Money. I built the system in 2000, and there was no economic alternative to Pb/A at that time.

Second aspect is "Why Group 31 size?" They are the largest storage capacity that I can easily carry by myself. When I do need to change batteries (they last 5-10 years) I can lift them out and put them on deck without mechanical assistance.

Chris

 

And now?

So, knowing what you know, having lived with that system for a long time, if you had to set it all up again today from scratch, what might you do differently? For example, would you choose lithium ion now or avoid them for the same (or another) reason? Any other changes?

 

Hmmm...interesting question.

Phil pointed out that I don't need the house batteries, I could get rid of them and save a few pounds.

I would love to have a different battery chemistry but I can't afford it.

I would love to have a below-decks installed diesel generator instead of gasoline.

I would opt for better cooling. I have seen some lovely water-cooled motors on the market since my day. (My motor has occasionally gone into thermal protection shut down after a long day of steaming.)

I would like to have a bigger charger capacity. I am limited to 30A charging, and this doesn't load the Honda to 100%, but it _does_ limit me to 30A throttle when I am running in "gasoline fueled w/ electric transmission" mode.

I would like to have a wind-powered charger. My PV work great, but on some days there is wind and no sun.

 

Enlightening

Thanks for the very informative reply, Chris. I'll probably bug you again on this topic at some point. And Happy New Year.

 

Happy to be of service! As I've said all along: It's not for everybody, but it has worked for us for 15 years+.

 

"I would love to have a different battery chemistry but I can't afford it.

Oh, why the Group 31 Trojans: "

Most gp 31 I have seen were truck starting batteries , not deep cycle batteries at all.

Perhaps a real deep cycle configuration would give the batt longevity boost , and power supply as well as different chemistry?

 

Fred: Mine are truly deep cycle: http://www.trojanbattery.com/product/t-1275/

Trojan has an excellent summary of their product line, divided into several groups. Here is the section that includes the T-1275: http://www.trojanbattery.com/products/deep-cycle-flooded/signature-line-flooded-2/

 

Justaguy - thanks for starting new thread - and not hijacking.
Thanks CmcK for great info,
And to all for regs discussion and battery discussion - very useful.
HNY to all

 

Trojan t-1275/ is not a Series 31, dimensions are close , but taller.

The 31's are usually start batts only.

The 1275 are fine for those with the extra height to fit them , and really are Deep Cycle.

 

Not sure what the point of the argument is here. You can buy gp31 deep cycle batts at Walmart/Sams Club. The majority are dual purpose. These work just fine for me. I use them on my sailboat so that all are the same. They often have a bit better recharge ability, also. There seems to be a longstanding bias against dual purpose batts as being not "true" deep cycle batteries, and I feel this is undeserved in the larger sizes and better technologies. No reason a gp 31 deepcyle AGM shouldn't deliver 800 CCA. It sacrifices nothing.

http://www.samsclub.com/sams/durace...rv-battery-group-size-31dtmagm/prod3590232.ip