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Old 10-26-2021, 01:17 PM   #1
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Does shore power bypass the batteries?

Hi there,

I'm trying to understand how the electrical system on my bus works when hooked up to shore power, wondering if anybody here might have insight.

I have a solar hook up, which charges 4 deep cycle batteries, which then goes through the charge controller, and up to the inverter (I believe). However during the Seattle winters we don't get nearly enough sun to power the bus so we rely on shore power. I just recently had to move the bus to a friends property which I am using for shore power.

He just found out though that his electrical system is pretty significantly taxed and if the bus used a ton of power during the winter (which it concievably could because of heating etc.) It could damage his electrical system.

So here's the just of my question.

With shore power, does the current go:

power source -> electrical output (fridge etc.) ---(leftover current)---> battery bank

Or

power source --> battery bank ---> electrical output?

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Old 10-26-2021, 02:03 PM   #2
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Depends on your system. I can tell my solar system to either charge or run the bus or both OR bypass depending on if I'm connected to shore power or not.

You'll probably need to find your equipment manuals, on line if you haven't, to determine how yours is configured. Good Luck.
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Old 10-26-2021, 02:18 PM   #3
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Look at your inverter and find the model number. If itís an ďinverter/chargerĒ then itís usually gonna charge your batteries when itís plugged in and you may or may not have a choice about that.

If you have a transfer switch to switch between shore and battery power then you likely donít have an inverter charger and likely have a separate charger that you may or may not be able to turn off.

It all depends but the good news is that if you remain plugged in for a significant amount of time the usage will likely taper when the batteries are full and itíll remain lower.
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Old 10-26-2021, 04:47 PM   #4
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It depends how you have it setup. Did you build your bus electrical system or buy it prebuilt (or pay someone to do the electrical work)?

1.
I am no expert when it comes to shore power, but my understanding is that in the shorepower centric usual/traditional RV sense (which seems to be the way many on this forum design/build their systems), a shorepower connection bypasses the battery bank/DC system, connecting your Bus 120 VAC system to the shore 120 VAC directly, and the only connection with the DC system/batteries would be through a battery charger/'converter'

Shorepower --> Bus 120/240 VAC System

2.
However if you designed your system in a different way, you might have an inverter/charger which might either 'pass through' power to your 120 VAC system and charge the batteries, and/or some hybrid solution utilizing both shore and battery power as a supplement.


Shorepower --> Inverter/Charger --> Bus 120/240 VAC & Battery Bank



3.
A third (less common) possibility is a shorepower system that *only* charges your batteries and everything else draws from the batteries. This is more common in the marine or overland vehicel world then among skoolie folks, so unless you specifically designed the system this way, its probably not what you have.

Shorepower --> Charger --> Battery Bank --> Inverter --> Bus 120/240 VAC


If your system is some version of option 2, and your inverter/charger is programmable, you may be able to limit what is passed through or at the very least limit charging to some amount your friend was comfortable with.
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Old 10-26-2021, 04:56 PM   #5
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But to the spirit of your question, its likely not the battery bank that would be the big issue for your friend, its the high draw devices you might use, you mentioned heat, do you use electric heat? What other high power devices might you use? And what is your shorepower connection 15/20A (<=2400W), 30A (3600W), or 50A (12,000W)?


And in what sense does your friend think his system is overtaxed?
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Old 10-26-2021, 05:04 PM   #6
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Yes, as with many "straightforward" questions on complex topics

it depends.

IMO you should not even be operating your systems without knowing how it works, but...

_______
My personal preference is a design where everything runs off the battery bank discharge buss

with an emphasis on "extreme" energy efficiency, as if living off grid with very limited energy inputs.

Thus very few AC appliances requiring inverter output.

Then the only input from shore power is into the battery charger.

______
The only exception would be high load appliances that cannot (should not) run off stored energy

IOW only run off shore power or generator, aircon being a prime example.

These I would wire for simplicity to get a separate direct shore power plug, not dealing with AC fuse/distribution/grounding issues internal to my rig.
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Old 10-26-2021, 05:10 PM   #7
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Originally Posted by retrouvailles View Post
He just found out though that his electrical system is pretty significantly taxed and if the bus used a ton of power during the winter (which it concievably could because of heating etc.) It could damage his electrical system.
Not a thing.

What specific components are being "significantly taxed" and in danger of being damaged?
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Old 10-26-2021, 05:11 PM   #8
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Significant heating (air, water, engine) is another function that should not usually be included in the stored DC power side of the design.

Supplementary systems can be designed to only take advantage of shore power when it happens to be available, same as waste heat from the engine while traveling

but primary heat sources should be direct burning of fuels like diesel or propane.
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Old 10-26-2021, 05:27 PM   #9
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Not a thing.

What specific components are being "significantly taxed" and in danger of being damaged?
He might be referring to the house panel.

For instance, my house has a 100 amp panel and service, it's older, and that was sufficient when built 75 years ago. Previous owner installed an electric water heater, and we've since added a furnace/heat pump/ac system to it. Couple that with an electric stove/range and an electric dryer, and I'd say we're close to 100 amps if all of that would be on at once.

Add a 30 amp camper pedestal with a school bus on it, and I know we'd be over for sure.
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Old 10-26-2021, 07:06 PM   #10
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shore power should bypass your batteries.

if your solar will maintain the batteries then i'd let them be and get the inverter out of the loop. go to 100% shore power.

i plugged in and lived in my bus for a couple of years and the battery chargers overcharged my battery bank and fried a nonused bank. it was my fault, i stopped checking to see if my batteries needed water.

you can't (illegal) back feed the shore system with your inverter, it should be locked out when on shore power.

good luck
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Old 10-26-2021, 07:37 PM   #11
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if your solar will maintain the batteries then i'd let them be and get the inverter out of the loop. go to 100% shore power.

I think you might be misinterpreting the context of the post here (or maybe I am, its not 100% clear).



OP's potential host/friend is worried about the bus overtaxing the shore/home electrical system. I think probably the goal is probably to minimize (or at least flatten out) use of shorepower, not maximize it.
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Old 10-26-2021, 07:51 PM   #12
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you are corrct, i didnt read the post thru.

get a 100#propane tank and buddy heater, then hook up to the friends shore.
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Old 10-26-2021, 10:50 PM   #13
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One half solution might be to only connect to shore during the nights to recharge the batteries after the friend is asleep and no longer using large loads themself. But this assumes you dont have any large loads that must be run during the day that could not be powered via battery.
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Old 10-27-2021, 01:54 AM   #14
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get a 100#propane tank and buddy heater, then hook up to the friends shore.
Propane is great, but get a heater that vents to the outside, especially if the location has humidity.

Buddy puts out plenty of heat but also lots of water vapour

can lead to condensation issues and thus mold
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Old 10-27-2021, 03:16 AM   #15
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In the "new Crown" I am using three sources that can charge the battery bank. Different configurations are used depending on what I am doing at the given time.
1) If driving from point A to point B the second alternator supplies up to 250 Amps to the DC bus. If while I am driving I want to run air conditioning, I would turn on the Main inverter to run the air.
If the above is true and it is daylight hours the solar array on the roof will also supply power to the DC bus.


2) If I am stationary and I have outside power available I would turn off the main and small inverters. The RV battery charger will supply up to 65 amps to charge batteries. If it is in daylight hours the solar array will add to the power supplied to the batteries. Air conditioners, fridge, microwave, washing machine, clothes dryer, etc all runs of shore power.


3) If I am stationary and no outside power is available, I have the option of running the generator, which supplies power like outside power. The RV battery charger charges up to 65 amps plus what the solar array provides during daylight hours. With the generator running no inverters are used.


4) If I am stationary and I am not running the generator and switch off the main inverter, my lighting still works, my water pump still works, all 12 VDC. My fridge is 120 VAC only, so for that and my CPAP I have a 300 watt sine wave inverter that will power just those. If or when I bring main power (120 VAC) on line (outside, generator, main inverter) the power for the fridge and CPAP is switched over to that source automatically.


The operation of the solar and RV charger is automatic. The small inverter needs to be manually turned on/off. The second alternator is working whenever the bus engine is running.


The generator is started/stopped remotely from inside.

The main inverter is turned on/off remotely.


The outside power cannot be connected to generator or the inverters output. I manually switch between outside or generator or inside inverter power by switching mechanically linked pairs of circuit breakers in the electrical panel. The mechanical linkage makes it not possible to have both sources switched on together. To use the main inverter a second pair of breakers switches between generator/outside or inverter. The inverter does not supply power to all ac appliances in the bus by design (including the RV charger).


All but two lights in the bus run on 12 VDC. Two art deco lights will run on 120 VAC but will have LED bulbs in them.


The solar array will supply power to the batteries anytime there is daylight.


The main inverter is 3000 watts.
The generator is 6.5 kw
The solar array will supply 1 kw.


All AC circuits have power when sourcing from generator or outside power.


The RV batteries are not cross connected to the bus batteries.


I am planning an switchable emergency cross connect between the bus and RV batteries so if the bus batteries get too low I have a backup capability.


My outside power is a 50 amp service. The generator is a 30 amp service (240 VAC). The main inverter will supply up to 25 amps continuous(120 VAC). At maximum output I expect about 70 amps at 14 volts from the solar array.


If I only use the lighting and the furnace I expect about 20 amp at 12 VDC. Add another 15 amps for the fridge (using small inverter). I would only turn on lights where I am in the bus.

If connected to outside power I expect that 10 amps of current flow from outside power would be enough. Add the TV and stereo that would double at least. Those figures are peak usage, such as when the compressor in the fridge is running, and the furnace is blowing and burning. Any others wish to comment?
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Old 10-27-2021, 11:48 AM   #16
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Flattracker's setup is about as gold plated as you can get! What's cool is it shows how far one can go with electrical to accomodate all conditions.
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Old 10-30-2021, 06:03 PM   #17
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There are so many different ways to wire a bus, I wouldn't dare give a definitive answer to the O.P.'s question. I suggest doing some investigating and exploring what you have. A multimeter would be a good tool to use. With solar panels and shore power disconnected, test the voltages of your batteries. A fully charged 12v battery should read about 12.7v. Plug into shore power, and take battery readings again. A charging voltage should be at least 13.4v. Unplug and see what solar is providing in daylight. It should also be about 13.4v.

Are you going to live in the bus at your friend's property? If not, why leave the fridge and heaters on? Far better to winterize the water system and leave the fridge door open a bit for the storage period.

If not driving the bus, the engine battery could be removed and stored at home on a trickle charger. The same for the house batteries if you're not living in the bus.

I would suggest if your bus isn't equipped with one, installing a battery isolator between the house and chassis batteries. This would prevent the batteries from draining down to the weakest voltage but connect them when a charging voltage is present.
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Old 10-30-2021, 10:05 PM   #18
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Quote:
Originally Posted by retrouvailles View Post
Hi there,

I'm trying to understand how the electrical system on my bus works when hooked up to shore power, wondering if anybody here might have insight.

I have a solar hook up, which charges 4 deep cycle batteries, which then goes through the charge controller, and up to the inverter (I believe). However during the Seattle winters we don't get nearly enough sun to power the bus so we rely on shore power. I just recently had to move the bus to a friends property which I am using for shore power.

He just found out though that his electrical system is pretty significantly taxed and if the bus used a ton of power during the winter (which it concievably could because of heating etc.) It could damage his electrical system.

So here's the just of my question.

With shore power, does the current go:

power source -> electrical output (fridge etc.) ---(leftover current)---> battery bank

Or

power source --> battery bank ---> electrical output?

I can't answer your question, but I do have a suggestion. Charge your batteries during low use by your friend such as while sleeping or they are all gone- school, work, ect. Then use your batteries while they are using high wattage. Alternative - you could pay to have a larger service or second RV service installed. What are you doing for sewage and water?
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Old 10-31-2021, 04:42 AM   #19
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Even if my bus is running from outside power or generator or the engine is running, all of my 12 VDC circuits still get power from the main 12 VDC bus (through appropriate sized breakers) I expect that if all of my 12 VDC circuits are running at max current flow, (worst case scenario) the RV charger is capable by itself of supplying enough current to power them. If the engine is not running,and I am connected to outside power or the generator is running the RV charger is enough to maintain the batteries. If it is in daylight hours, the solar array also provides more than enough power (in good sunlight) to maintain the batteries at max 12 VDC load.

In my case the solar array, the RV charger, and the second alternator all supply current flow to the main bus. At night, not connected to outside power or generator, engine not running, no sources are charging the battery bank, and things can discharge the batteries.


For that reason I have a second smaller capacity inverter to supply 120 VAC (sine wave) power to just the fridge and my CPAP machine. This will be my mode of operation when maybe at a rest stop or side of the road. Those two items are the only critical AC powered devices that really need AC power.


The furnaces run on DC power and can draw down batteries. I think with the appropriate sized battery bank I should be able to last the night. Once sunlight returns, the solar array will start replenishing the batteries through the main DC bus. Starting up the generator would add to that replenishment.

How you configure your electrical system will make the difference. My design is certainly not the only way to do things. I think having a main bus handling the current flow for all of your DC circuits, and passing current to power all of your DC needs and keep the battery bank charged is a good way.

Based on experience, I suggest keeping the RV electrics separate is important. I almost got stranded in Ventura after a flat track race because I left the fridge running all day from an inverter connected to the bus batteries. I barely got the bus engine started with the batteries from being somewhat discharged. At the time the "old Crown" did not have a generator. I never did put a solar array on the old Crown. Later when I did put the generator in, running all day was not desirable either. A few hundred watts of solar would have been enough to keep the fridge happy.


An attempt at a simple answer is:


If you have in your electrical system the means to charge your battery bank when electrical usage is occurring, some or all of the electrical power comes from the battery charging source. If you are connected to outside power, than those sources to charge the batteries supplant the energy taken from batteries.



I would also state that if your friend's house, if built to electrical codes would not be harmed by your electrical consumption. In the worst case, if your draw more current than the circuit your connected to is designed to provide, either a circuit breaker will trip, or a fuse will blow. Is it possible your friend's concern is more the cost of providing power to you than any damage you could cause?


One last suggestion: Protect ALL circuits with breakers or fuses. There is nothing like having a short smoking wires with nearly infinite current available and you can't reach the wire to cut it or turn off the power.


Wires in your RV could get hot enough to glow orange. (and start a fire)
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