System for a 40' bus.

retep · February 2015

I have been reading this forum and links for a few weeks now 'till my eyes crossed and my T is dotted. I hope a couple of you far more knowledgeable and understanding gurus will look over these plans and see if I have managed to invert the aforementioned condition.

This is for a friend's 40' bus with electric 'fridge (0.62 kwh/day this last month) and electric water heater (unknown kwh/day). 6 (Costco) golf cart batteries in 3 strings of 2 for 660A @ 12V. This battery bank is for both the house and starting. (I have liberated room in the battery/engine compartment for 2 more batteries.) A Trimetric 2030 is on hand, and its 1000A/100mV shunt for the negative side once we rewire her batteries (and I would love to see a fuse and cutoff switch on each string). The 1000A shunt is due to the near 1000 amp starter which spins the 2-stroke Detroit Diesel 6V92T to life. In conversation, Bogart Engineering said the Trimetric will be OK.
She (the friend and the bus) has 6 Hanwha 305 watt panels, 1830 watts total. VOC-45.7, ISC-8.8, VMP-36.7, IMP-8.32, 1x2-meter panels to be mounted at a 2 degree pitch (she cannot get on the roof and tilt). The panels were quite a deal, and allow for poorer insolation days. From there separate 10 gauge THHN from each panel in PVC conduit, the longest panel run being about 30'. I was planning on a combiner on the roof with #6 to the solar controller, but the voltage drop seems to be half using separate #10 for each panel to an indoor combiner. I have crafted a fuse block/buss bar with 6 15A (per panels' spec) ceramic fuses. It will fit into the wiring space on a GE air conditioner disconnect (rated at 60A, 120V, but we have fine-tuned its construction to give around 50% more contact area on its knife blade - I think it will be OK).

About 6 inches of #4 welding cable will run from the combiner buss into a Midnite Classic Lite 150. (With the 6, 15A panel fuses right there, do I need another fuse between them and the Classic?) (limit the output on the Classic 150 to 66amps- 10% of the batteries' amperage) Then back through the a/c disconnect, then maybe a 100A fuse on 2 foot of #4 to the inverter lugs. From there to the batteries is 16 feet. (Way too long - there is no other place except in the engine compartment, next to the batteries.) Currently there is 1/0 wire feeding the inverter, we could pair a second run of 1/0, but with no certain way to match the lengths. I can, alternatively, give a new 1/0 pair to the Classic.
The 1/0 is already in possession, as is #6 and a spool of #10. As best as I can guess, from what I have read, the only place I want to ground this is the panels' frames to the bus, and the negative at the non battery side of the shunt.

Until all is running, and I can wrap my brain around how to set-up waste not to switch the water heater, I will be advising the bus owner to switch off her water heater at the breaker near dusk, and not re-energize it until the Trimetric says batteries are full.

I plan on just connecting only one panel until I get the Classic programed via the local app. Is there a possibility that the Classic will loose it's settings and boil the batteries or let the magic smoke out of the controller? Should I limit it's output with a smaller fuse, such as an 80amp?

Thank you for any help, ideas, suggestion, and corrections. -Peter.

retep · February 2015

Thank you for your help Bill.

Even using 4/0 for my 16' run to the batteries will give me:
Voltage drop: 0.15
Voltage drop percentage: 1.03%
Voltage at the end: 14.35
(97A, 14.5V)

The calculator gives the same drop for 2 runs of 1/0, which I have on hand. The routing and length will not be be samefor the two runs though. How much this will affect the load sharing between the runs, I have no idea.

Even the 250 amp breakers you linked to would probably be blown by the 1000 amp starter. She never runs it for more than 5 seconds at a shot, and usually only twice to start, but that's over 300 amps a string instantaneous, though well under 1/100 of her batteries' capacity.

She is considering putting 2 starting batteries in the newly liberated space with a 110v battery float charger on them (which will then keep the inverter always on?), but we will lose the ability to fully monitor them with the Trimetric, and the extra day of grace for poor weather that adding to the house bank (when it's time to replace batteries) would give her. She does have a huge diesel generator with it's own starting battery if the house batteries should go flat.

Any further thoughts, corrections, or pointing out of blunders will be appreciated. Thanks- Peter.

BB. · February 2015

Two parallel cable runs will be -3awg heavier, or look at each now has 1/2 the current, so 1/2 the voltage drop.

Realistically, a conservative design would be C/2.5 discharge.

660/2.5 = 264 amps surge

At least that is the derating we normally use.

Fuses and breakers do have a thermal delay. But if that is enough for cranking an engine.... don't know.

-Bill

Iceni John · February 2015

Peter,

I also have a 40' bus with a full PV setup. However, your having just one combined SLI and house battery bank makes me nervous. I also have a 6V92 engine - will deep-cycle batteries alone supply enough amps to start it? I'm keeping my start and house battery systems separate, but with an intertie between them so in an emergency I can link my house batteries to the starter. For this reason I'll be using two Group 31 batteries instead of the two 8Ds I now have - their Reserve Capacity isn't as high as 8Ds', but that won't matter much if I can switch 900Ah of house batteries to the starter.

Something else that slightly concerns me: you said that some of the batteries will be in the engine room? The heat given off by a 2-stroke is enormous, so those batteries there may have a shorter life than if they were somewhere else cooler. Plus, when charging them they will need their own battery temperature sensor, because they'll be much hotter than the other batteries due to their location.

John

retep · February 2015

Thank you for your reply John.

All of the batteries (except the generator's starting battery) are in the rear engine compartment. That is the way Bluebird designed the bus, and it has been that way since it was built in '85. It has been starting with the 6 Golf cart batteries for a couple of years now, and though asking for 300 amps from each 220 amp hour string seems excessive, it is only for a few seconds at a time.

I just called the bus owner- she says she was forbidden by the Wanderlodge Owners Group, from allowing the starter to run for more than 30 seconds. Her usual is, when cold, to run the block heater for an hour, crank it for 20 seconds, give it 5 minutes, then 15 second cranks a couple of minutes apart, and it might take 4 such cranks if she has been parked a long time. Which comes to around 23 amp hours total or 8 amp hours per string If I have figured this right, not including the block heater, which I have no idea of how it is wired, how much it takes, or whether it is ac or dc.

Yes, it is a 6V92 engine.

Once the batteries are reinstalled with proper matched length and gauge cables and the Trimetric in place, we will discover just what percentage it is taking from the batteries to start this beast.

I have sung the praises of a second, separate 24 or 48 volt bank for the inverter, but that would require a new inverter also. She is contemplating, if all works well, removing the 12.5Kw generator from the front of the bus and replacing it with a much smaller, lighter one and a shiny new house bank. Meanwhile, what she has is already there, and she will have much more information in the future to base decisions upon.

I have previously read your earlier postings, John, and mused that I would sure love to be the person you (or your heirs) sell your bus to in the hopefully far future (which will count me out) I'm hoping pictures will come soon.

Thanks- Peter.

Audiomaker · February 2015

I have a battery charger (marine style) which by a switch can charge (the separate) vehicle bank from either the house bank (via inverter), or by shore power (or generator).

I'm not really too concerned about monitoring my starter bank (4 grp31's). When I'm off grid (which is always right now), I have the marine charger switched only to generator input, so it turns on *only* when the generator is running.

In the future I plan to incorporate a separate automatic generator start for the vehicle bank whereby if I leave the headlights on (or whatever), the generator will kick on and charge the bank (both banks).

While not pertaining to this topic, I also plan to install a separate 2kw inverter to the vehicle bank with an ignition lockout (Xantrex ProWatt 2000) and have this power a separate charger for the house batteries.

This will allow emergency AC power from the vehicle batteries if there's a problem with the house system, but also will charge the house bank from the vehicle batt's *only when the ignition is on*. Therefor I'll be charging the house banks with the alternator when going down the road.

The reason I don't do a switch to directly connect the house and vehicle banks is because I don't want my alternator charging the house banks...it's "dumb". By powering a charger from an additional inverter I can get "smart" charging while I'm going down the road. The other reason is that my house bank is 48v...which doesn't play well with a 12v starter bank.

Bottom line is that when the engine is running, it charges the house bank, and when the engine is not running, the house system charges the vehicle bank.

Not much else to add except that I can't imagine powering a water heater from my batt's... that's what propane is for. It's an interesting concept using a diverter system, but I think I'd just get some sort of wood fired hot water heater if no propane or grid power were available.

Iceni John · February 2015

retep wrote: »

Thank you for your reply John.

I just called the bus owner- she says she was forbidden by the Wanderlodge Owners Group, from allowing the starter to run for more than 30 seconds. Her usual is, when cold, to run the block heater for an hour, crank it for 20 seconds, give it 5 minutes, then 15 second cranks a couple of minutes apart, and it might take 4 such cranks if she has been parked a long time. Which comes to around 23 amp hours total or 8 amp hours per string If I have figured this right, not including the block heater, which I have no idea of how it is wired, how much it takes, or whether it is ac or dc.

Thanks- Peter.

Oooh ouch, I don't think I would ever crank my engine for 30 seconds straight! That's A LOT of current flowing through the starter's cables. Most 6V92s in buses (yes, a PT40 Wanderlodge is still essentially a bus!) have 42MT starters that are rated at about 10HP, so theoretically they could pull thousands of amps for a few seconds. However, a healthy Detroit 2-stroke should start within one or two turns of the crankshaft, unless it's cold in which case all bets are off. Then, either a judicious whiff of ether (but no more than a one second spritz) in the intake, or a block heater, or the old Crank-For-10-Seconds-And-Rest-For-A-Minute trick that will eventually soak enough compression heat into a ton of iron that it will splutter to life on a few cylinders before all six decide to join the party. And while that's happening, you'll be able to kill all mosquitoes within a three-county radius from the biblical amounts of grey smoke it will spew out. Fun!

And that's why it's so important to have good cables and connections for the starter - even just one bad ground or corroded lug can heat up to melting point in a few seconds. An IR thermometer is good for detecting any such bad wiring, as well as for checking temperatures of tires/brakes/hubs/manifolds/radiator/etc every hour or two during a trip.

Yes, block heaters are A Good Thing. They can prolong the life of the starter, provided they don't run down the starting batteries while warming the engine - now that would be cruel irony, with the engine warm enough to start but having no more power to start it.

Where is this bus located? I'm also wondering if the non-tiltable panels on it may be producing much less than their rated power due to them not facing the sun well enough.

John

Iceni John · February 2015

retep wrote: »

Thanks John.

The bus is currently in Conroe Texas, near Houston.

The owner does have an IR thermometer, and has melted the lug on a battery. The batteries had quite a selection of gauges and lengths of wiring, and 3 different grounding points. Currently, the positive has what looks like 4 feet of #1 cable to the 1000A starter, from there, it is daisy-chained another 5 feet to the 2 in series 500A shunts at the start of the house wiring spaghetti bowl. The batteries are now out of the bus awaiting a total rewiring, a common ground point for the 1000A negative shunt the Trimetric requires, and new thicker gauges at least at the start of the system.

Thanks- Peter

The starter draws the most current, so it should have its own 4/0 positive and negative cables running directly from the batteries to the starter itself. The bus frame should never be the primary return path for the starter's current. Anything less than 4/0 for the starter will cause problems - yes, 4/0 isn't cheap, but some things just need to be done right, and that's one of them. House loads can use less-heavy cable such as 2/0 or 0, depending on what the maximum draw will be - the inverter will determine what size house cable to use. Any battery isolator switches must be able to handle the loads - for house loads the Blue Sea m-Series switches are rated at 300A continuous, and for the starter the larger e-Series at up to 2,000A for 10 seconds, or the HD-Series at up to 2,750A for 10 seconds (that should be more than enough for a 6V92!).

It sounds like the entire wiring needs to be reconfigured. Daisy-chaining anything is not a good idea. Good luck with that project!

John

System for a 40' bus.

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