house batteries charge time

[squazo]

Hey everyone, I have a question that is related to owning an RV but that is not about RV's. It is about batteries.

I am helping a friend convert a box truck into a portable dog grooming business. She is already very successful with the one she has and is looking to hire a groomer to operate a second vehicle. I am quite capable of the welding and carpentry work however the electrical system on a vehicle is totally foreign to me. She would like to be able to run the equipment on

a generator

shore power

and what I believe are called house or coach batteries.

I have a question about charging the house batteries. Are they charged by the vehicles alternator? If so how long does that typically take? The thing is, unlike driving cross country like one would in a RV she typically drives for 20 minutes or less, shuts off the engine and then grooms a dog on generator or shore power. So I personally think the amount of time she is driving would be completely insufficient for charging a set of house batteries.

Generally the house batteries are only used to operate lights for limited times, before or after the generator/shore power is available.

So how would you guys go about charging these house batteries?

 

[Isaac-1]

Generally speaking you will also have a "converter" which is a battery charger powered by the generator, so that any time the generator is running some of that power is going towards recharging the batteries, as well as running those DC power loads like the lighting.

There may be ways to set this up so that the generator does not have to run all the time that the dog grooming equipment needs to run by means of adding an inverter which turns DC battery power into 120V AC wall current, which is typically needed to run higher power items.

I see that you are in Louisiana (I live in the western part of the state), knowing the climate here she will likely need to run a generator anytime she needs to run the main air conditioner, which means about 8-9 months out of the year here, so any attempted to save generator run time may result in minimal success.

 

[DonTom]

have a question about charging the house batteries. Are they charged by the vehicles alternator? If so how long does that typically take?

Yes. Perhaps a day's trip down the freeway if totally discharged. But it depends on the KWH /AH capacity of the battery. The more battery in KWH the longer it will take for the vehicle's alternator to fully charge it from near empty. Keeping the house battery charged is usually no issue if on shore power, driving or even using the generator for a few hours per day. But then it depends on the size of the converter as well as the KWH capacity of the battery.

To see where you're at with the house battery, install a SmartShunt. That will show the SOC (State of Charge) of the house battery. A 50% SOC means it is half discharged. 100% SOC means it is fully charged. That is usually when you want to turn off your generator, if it is being used to charge it. If driving, or on shore power, you don't have to do anything when it is fully charged.

The Smartshunt also shows MUCH other handy info. WRT your house battery.

-Don- Auburn, CA

 

[squazo]

How does one go about figuring how much charging capacity their vehicle has? How are alternators rated? Is it by amps, I guess I'm just trying to figure out how many batteries we can charge and how long it would take to charge them from fully dead. I know I need specific amount of power consumption to get an actual number but right now I'm just trying to figure out in general terms so I can plug in all the wattages and run times later.

 

[Isaac-1]

Alternators are rated by amps, but most are not intended to output their full rated power level for more than a few minutes at a time, ie to recover power into a starting battery after cranking the engine, etc. At typical automotive alternator is designed for a 30% duty cycle, ie about 5 minutes on then 12 minutes off. There are however special high output alternators that are designed to handle higher running loads.

 

[RedT]

Since she has a mobile dog grooming vehicle now, why not check that layout and copy it. I would think she would want an air-conditioner, water pump, 115 volt AC for a blower, etc. That configuration would require an on-board AC generator and/or shore power. With a converter (that is also a charger) any time she has AC power, the batteries would be charging.

 

[squazo]

I am leaning heavily to generator and shore power with battery back ups that can only be charged from the generator or shore power. Does anyone see any issues with this?

I dont really think I know enough about alternators to attach that to a battery system, also I dont think the short drive distances will charge the batteries. Plus the truck probably does not have a heavy duty alternator.

 

[Mark_K5LXP]

Since very few of the proposed loads can be run from batteries, why the concern for recharge time? About the most they'd be used for is some lights or maybe vent fans until the genset is started, or shore power is connected.

Mark B.
Albuquerque, NM

 

[squazo]

She would like to be able to finish an appointment on batteries just in case the generator fails and there is no shore power available. I think we are going to have to just have it set up so the batteries are charged only from the generators or shore power.

This is a possibility with her current van so we would like it possible in the new one we are making. Yes, it is a lot of batteries, and they are very expensive.

 

[squazo]

What kind of selector switch do you guys use to switch from generator to shore to battery power?

 

[Jayflight]

Choose the proper generator, like the inverter generator. And of course you should figure out the fuel setup and how you plan on feeding it. Your generator may not have a fuel pump, if it has a built in tank now. So all that is a consideration.

 

[Gary RV_Wizard]

What kind of selector switch do you guys use to switch from generator to shore to battery power?

The most convenient is something called an Auto Transfer Switch, which senses which source has power and uses it. If both generator and shore are available, it chooses generator (called generator priority). They are readily available for 50A/240v aad 30A/120v sources. Here are some examples:

https://www.etrailer.com/dept-pg-RV_Transfer_Switch.aspx

 

[Isaac-1]

If she needs to finish an appointment on battery power and has relatively high amp draw appliances like hair dryers, etc she will need an inverter, and a relatively large battery bank, something along the lines of this which will both charge the batteries when connected to shore power, and convert the DC power back into AC power to run up to 2000 watts worth of AC load (a hair dryer draws about 1,500 watts): https://www.amazon.com/Renogy-PCL1-20111S-Inverter-Charger-Compatibility/dp/B07PQR8HVQ/

Renogy is a mid tier brand, there are certainly better / more expensive options, and there is also a lot of cheap junk inverters out there.

 

[squazo]

I like those transfer switches. I wonder if two can be run in line to be able to switch between all three power sources.

 

[DonTom]

ie about 5 minutes on then 12 minutes off.

Are you referring to "Smart Alternators" or did you mean they switch to a lower current? AFAIK "off" only refers to the "Smart Alternators" which AFAIK I have not had in any of my vehicles, unless there is one in my Ford 2022 7.3L RV. I never checked for it in it.

-Don- Auburn, CA

 

[squazo]

I almost found a solution. I found this very cool transfer swich that has a plug on it for your convertor and that plug is only hot when the transfer switch is on shore power. Which means the inverter wont power its own charger. Pretty slick!!! but the transfer switch is only rated for 30 amps. I need a 50 amper. It is the domitec pre wired transfer switch. Any one got any idea where to find a transfer switch with this feature at 50 amps?