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Kevin, Licensed Electrical Contractor
Category: Electrical
Satisfied Customers: 3588
Experience:  30 years Licensed Electrical Contractor in Illinois, Adjunct College Electrical Instructor, Former Electrical Inspector, Diploma: Digital Electronics, FCC Technician License
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Selecting the Charge source. I can charge the batteries off

Customer Question

Selecting the Charge source.
I can charge the batteries off the genny by simply using a branch circuit. I'll just have to be careful about my max load on the genny.The other source would be shore power, so now I have the question of shore -> Fridges or Shore -> Charger if I only have a 120/15 line.I'm thinking I can put the Shore line to the charger AND let the fridge run off the batteries while charging. Any issues with that?as long as the batteries are not dead to start with it also resolves the issue of simultaneous start up loads tripping the shore line breaker because the batteries will supply it.It would be simpler to wire it so I always go through the batteries when hooked to shore so I never have the load/tripping issue or dead battery issue.It will shorten the life of the batteries. I think mine are rated at 700 cycles, so it would make them about 2 year batteries (they are rated at 7 years.) But losing one fridge full of meat would cost as much as the batteries.Do you see any issues with this?if not, then
- the DPDT switch always connects to inverter in position 2.
- The shore line always connects to charger
- Don't need the SPDT switchThoughts?
Submitted: 1 year ago.
Category: Electrical
Expert:  Kevin replied 1 year ago.

Hello and welcome to Just Answer. My name is ***** ***** I will be happy to assist you with your electrical question.

1) I assume that the 2 fridges are only powered by 120 VAC or are they a combo 12 VDC and 120 VAC version?

2) If the fridges are only 120 VAC powered, the inverter still needs to be activated (ON position) in order to provide 120 volts from the battery bank to the 120 VAC fridges. If eliminating the SPDT manual transfer switch, then the 120 volts from the inverter would allow a back-feed via the DPDT disco switch due to the shore power connection back to the public utility grid during a commercial power outage. The purpose of the SPDT switch is to act as a manual transfer switch and isolate either inverter power or shore power.

Customer: replied 1 year ago.
I'm not following this one. maybe we're on different pagesAre you thinking Shore power through Sub panel to Charger? I was thinking shore power just to charger, then charger to battery to inverter to sub panel to fridges. All grounds would then follow the same path in reverse.Fridges are only 120v. They are standard UL commercial restaurant equipment. No RV stuff. Health code would not go for that.
Expert:  Kevin replied 1 year ago.

Yes, I was thinking Shore thru sub and then to the charger.

Your application will work, but keep in mind that if constantly re-charging the battery bank, this will slightly reduce the number of re-charge cycles.

Good the fridges are 120V models and not the combo DC/AC types.

Customer: replied 1 year ago.
Yea, I realize my battery life will be shorter, but it simplifies the design and removes a couple of risks that could cause a whole fridge/freezer of pork, beef, and chicken to spoil (that could be several hundred dollars) and risks serving bad food if I'm not aware of it.If I leave it over a couple of days in warm weather, I won't have to worry if the breaker tripped.
Expert:  Kevin replied 1 year ago.

Yes, I hear you on that. Considering the battery life will only shorten slightly, it does simplify the design and protects the food from spoiling.

Customer: replied 1 year ago.
There is another side issue here as well. How familiar are you with Deep cycle/inverter setups?It saves my almost $800/mo if I use the batteries every night instead of shore power.
[Reason: A commissary is required by code. If use a Commercial Commisay in the (bay area) it costs $900/mo and all you get is a fenced parking lot with a power hookup (might be 240V idk). but I can use a remote commissary for $400-$500/year and I have access to secure parking with out power for $65/mo. and i could use batteries at night]If I can do this,it's well worth replacing the batteries even if it's every 12-15 months.So, then my issue is getting enough charge into the batteries while operating to run the fridges over night without hitting a low voltage condition.Maybe you can check my thought/math on the issue. I'll just use rated/listed numbers for now (ignoring efficiencies and batteries not really delivery their rated amp hours)+ If the fridges take 14 amps and run half the time in warm weather over 16 hours, that would be 14 x 8 = 114 AH.
I'd need to spec out my batteries for more be safe. The last time I used a deep cycle I used a Trojan 12v 150Ah unit. Two of those would spec out at 300AH.+ The charger is a 110amp (12v) courtesy of Lynch. So theoretically it can recharge them in slightly over an hour.(See note below on this)+ The genny can put out 25 amps continous on each leg. 110amps 12v is only 11 amps at 120v, so it can supply the charger.But I'd have to push that back in from the genny during operating hours which raises a question of load. I can't really control the load the charger draws (Can I?) so if it's charging when all my other comes come up, I'll overload or trip the breaker on the genny.So unless i can moderate the charger some how, I'll need to run the genny just for the charger for say an hour a day. (at less than half load the 7000 should burn about 1/2 gallon per hour, so 20 days/month = 10 gallons/mo. Even if gas hits $4/gallon again it's $40/month. Right now it's about $25/mo.So can i moderate the charger?
maybe a smaller unit would be better?I assume the batteries /charger will draw less as the batteries get charged. Is that a gradual reduction proportional to the charge, or will they draw a lot until almost full and then drop off? if gradual, i could run the genny 1st thing in the morning as I'm setting up and while driving and by the time I start operating the draw will be lower. And the fridge draw will increase later as the day wrms up and they are opened and closed. So the loads distribute over time well.Note:
The charger can deliver 110 amps, but I'm not sure the batteries can draw or accept that much, or whether it's a good idea.
Both will get hot. I never like to run anything at max capacity. But i suspect the batteries couldn't draw or use that. More likely they will need a few hours (3? 4? 5?) and it's better for them any way.So that would reduce my load during operating hours. I'd need to measure amps to figure out how much, but if i run it first thing and while driving, maybe the load drops by half while operating? 5 amps would be 600 watts off the genny. I'll have to look over my loads again and see how that fits. Maybe i do some thing crazy and put the charger on a timer so it stops after a 2 hours when other loads are coming upYou thoughts? Ideas? Does this make sense?
Customer: replied 1 year ago.
At one point i looked at some fancy automatic transfer switches that could direct loads on demand. So if the fridges start up, it could turn the charger off. When they turn off, it supplies the charger again.
Nice device, except it cost as much as a car.
Customer: replied 1 year ago.
One other detail: Are you familiar with inverter brands? That's one item that's worth paying for reliability, I know cheaper units can be problematic and fail early.When i was a sys admin the server rooms environment controls would send me a text msg if the room temp got warm (bad news for big servers). maybe I need some thing like that on my fridges
Customer: replied 1 year ago.
ooops ... I calculated amp hours wrong. 14amp@ 120 ir [email protected], so draw over 8 hours is 1100AH. That's 10 hours on the charger. Just shoot me now :(
Expert:  Kevin replied 1 year ago.

Your calculations look good.

Whenever deep cycle batteries are installed, it is a general industry recommendation to double the quantity of amp hours that are required to support the loads. The industry always recommends a 50% amp hour reserve for those occasions when you may not be able to re-charge as fast. So basically, whatever the calculated amp hours are, then double that amount as a general rule of thumb if the budget allows for this.

Depending upon the battery, a full charge on a 12VDC battery will be in the range of low 13 to mid to high 13 volts. Once a 12 VDC battery gets below the 12 volt range, it is in a discharge state. Once a 12 VDC battery gets to nearing 11 volts, you're on borrowed time as it is pretty much discharged.

Trojan Deep Cycle batteries are a high quality brand, one of the best you can purchase in fact. unfortunately, they don't come cheap though:)

Re-charging the batteries on a higher current will result in a faster re-charge time, but higher current amounts will also result in a reduced battery life. Lower re-charging amps will prolong the battery life, but this may not be an option as you have food that needs to stay cold until you reach shore power or will need to fire up the genny.

I've only installed a few inverters such as AIMS and Energizer for my small PV system at my home. I am aware that Xantrex, Morning Star and Outback are the big inverter players in the solar world. Yes, you are correct on the cheap inverters. I've had a few of them crap out on me over the years.

I will ask my next door neighbor tomorrow when I see him. He has a fridge and freezer in his garage. When the inside temperature of the fridge and freezer is reduced, he has a T-Stat alarm unit that he purchased and it emits an audible alarm. It is just battery operated by a 9 volt battery I think. Although it does not send out any text message.

Customer: replied 1 year ago.
Trojans are pricey. I get them at a place in Northern CA that has the best price. Beats every place i've tried. My 150Ah 12v were $225I'm getting a crazy idea to have 2 sets of batteries. Hook up the big charger at home to charge over night, and swap out each day. I could make a tray to move them as a unit, use heavy cable plugs to make hook up easy, but still a pain.
It would allow putting a small charger in the truck (just to top them off) so load is not an issue.I'm looking for other atlernatives to park n plug in. I just really hate the $900 for a space n plug. Regulation created the problem and these places are taking advantage of it. The code has changed recently an the language around commissaries and storage has been loosened up to allow inspectors to yea or nay a location. I think they heard plenty about the problem it created (that code requirement was new in 2009). Some of them don't even had fenced yards, so the truck is vulnerable to vandalism. $900 for a plug.I appreciate asking your friend. The truck will have it's own phone account (used for visa charges) so if i can find an app for a phone I might be able to monitor fridge and batteries in real time, set alarms, etc (this brings out the techie in me ha ha ).Thanks for the inverter references. I'll check them out.
Customer: replied 1 year ago.
I think the Honda is a true sign wave generator, but I believe fridges will be fine on a modified sine inverter. Yes?
Customer: replied 1 year ago.
if i'm going to use batteries, I'm going to set up monitoring.
Do you have any resources for suppliers? I can stick to just electrical and monitor the battery voltage and the 120v line to the fridges. That'll tell me if the batteries are low or the inverter fails and give me earlier warning than temp.Do you know where I could find the hardware and software for line monitoring?
Expert:  Kevin replied 1 year ago.

That is a great price for a Trojan 150AH. I've seen them on some web sites selling for double that price.

Yes, having a set of back-up batteries is a good idea if the budget allows it. At the start of each work day, you will have a set of fully charged batteries.

I hear you on the $900 charge, that's a lot of coin every month.

A modified sine wave inverter will be about 20% less efficient as compared to a true sine wave inverter. Modified sine wave inverters may also generate a slight humming noise due to harmonics. Other than these 2 issues, the modified version will work OK on the fridge. Not the cleanest power, but will get the job done.

Yes, I will ask my neighbor tomorrow regarding his fridge/freezer T-Stat alarm. If the truck will have a data network interface device, there is a company that manufactures a Network Enabled Relay that can send out e-mails or text messages. Requires an RJ45 plug-in connection to a modem or a router. I believe it also works on iPhones. The relay contacts could be connected to an internal fridge T-Stat and provide you with alarm alerts based on the internal fridge temperature.

See link shown below for the Network Relay:

I designed and prototyped a low battery voltage monitor alarm circuit a few years ago. I was not able to locate a control panel that I could purchase for this application, so I built my own. The circuit is called a voltage comparator. Kinda of a pain to tweak the potentiometer (POT) and get the cutout voltage setting correct for the low voltage. I used my 12VDC power supply to tweak the POT and to adjust the cutout voltage. I set mine to alarm me at a 11.5 VDC cutout voltage. I built this comparator circuit panel for my solar panel application on my home where I use PV panels to provide emergency power for my 12 VDC battery back-up sump pump. I also use this control panel for emergency lighting in my home. When I loose commercial AC power due to a storm, I have selected ceiling fan lights in the home that turn ON within a few seconds on the loss of commercial power.

The cutout voltage on the VMA model could easily be wired to the above Network Relay to provide battery low voltage alarming status. The schematic shows a DC voltmeter. The picture does not have the voltmeter as it was my 1st prototype. Thus the only difference between the picture and the schematic.

Not sure where to obtain software for monitoring........ I'd have to research that.

See attached schematic, picture and parts list shown below:

Customer: replied 1 year ago. said they have inverters with remote monitoring capability. I'm waiting for a call back from them.What i need to do, unless you or a friend already know this, is just put a fridge on a deep cycle and see how much it drains and how long a given battery can last. Fridges vary, but if we account for the amps required on the fridge used compared to mine, we should get a general idea.My estimate of running 50% of the time might be way off. (and of course weather will affect it). But maybe it only runs 10 minutes/hour. That reduces the amp hours by 2/3 from my estimate. I might also move food into one fridge and turn the other off, reducing it by another third.The 1100 AH is way too high. But running one fridge 10min/hr gets it down to almost 200AH for a 16hr night.
I don't have a way to run a test at the moment. Do any of your Solar buddies have an idea how much battery it takes to keep their fridge cold?
Expert:  Kevin replied 1 year ago.

Thanks for the replies.

1) Yes, many of the higher end inverters have remote monitoring capabilties.

2) I've been asked this question before regarding the battery drain when a fridge is plugged into an inverter. Unfortunately, there is no immediate method to come up with a quick estimate due to some unknown variables. Every environment is different and not all fridges are the same in terms of size, Full Load Amps, temperature retention based on a quality built fridge, etc.

3) Yes, you are on the right track with your questions and thoughts in trying to get an estimate. I agree that a few tests would be required in order to get a fairly accurate of estimating and calculating the amp hour draw.

Once the variables shown below are known, then a amp hour draw calculation can be performed based upon the results.

A) The quantity of cycle times the compressor motor will turn ON/OFF in an average hour. Thus obtain an average run time.

B) Compressor cycle quantities per hour will also have an impact based on the external temperature as well as the internal fridge temperature. In other words, is there a large difference with the internal fridge temperature as compared to the outside temperature or nearby temperature surroundings?

C) Initial start-up on a warm fridge will have much more of a battery drain as compared to an already cold fridge. The compressor run time will be more frequent on a warm fridge as compared to an already cold fridge.

Expert:  Kevin replied 1 year ago.

Check out the links shown below for a fridge/freezer thermometer alarm:

The Thermoworks website manufactures a variety. Some can even remotely alarm to an iPhone or iPAD.

Here is a wireless model, but it doe not provide Cell or Tablet alarming:

Customer: replied 1 year ago.
I realize fridges and compressors vary, outside temp varies, how often it's opened, etc. Seems like the solar folks would have worked out some rough numbers. at the high end would be an older fridge in a warm climate in summer, at the low end would be a newer more efficient and well insulated fridge in a cooler climate. it would only take about 3 people listing their actual use, along with the climate, amp rating, etc. to get a general idea of a high and low figure.If i knew a good solar forum I would post the question.
On a side note: I'd love to set up an off the grid house or cabin. There are some places in CA where land is really affordable because it's remote. I've done some research on Cob and hale bale houses as well as Rocket stove heaters that would fit in nicely.
An earthen house with solar power and a rocket stove heater - maybe a little propane just to make cooking easy and run a backup genny in a pinch - could be totally independent of the grid (and very comfortable :)
Customer: replied 1 year ago.
A strange thing on this truck is i didn't find an inverter, or any disconnected cable that would have gone to one. Unless the charger is a dual charger inverter I'm not sure what he used. he had a bank of 4 deep cycles so it had to have one.The charger was custom made for Lynch, so getting docs is difficult. Here's a pic of it.
It has 2 12v terminals and one 120v plug and very little info on it.
Customer: replied 1 year ago.
Here's a radical idea.The Honda has electric start.
If i could monitor the fridge's compressor line, the genny could turn on at night when the fridge goes on.
I could leave the fridge on an inverter off a single battery, When fridge starts, genny starts and charges battery.
The fridge would never see a problem because the battery will provide start up power.A relay might work as a trigger. Then I'd need to set a timer to shut the genny off after a fixed amount of time (maybe 15 minutes)+ The battery should never get below 80% never needs a long charge time. Excess power through tout the day would keep it trickle charged.
+ Only need one battery
+ It will actually help the startup draw on the fridges 24/7 to have them hooked to the battery and the battery
+ I burn a little extra gas, but a far cry from $900Could you figure out how to wire a trigger?
Are you aware of some timer devices?I'd have to check, but the Honda start up is probably a 5 or 12volt line. I might be able to bypass the control panel altogether and just tap into the start and kill circuits.
Expert:  Kevin replied 1 year ago.

1) I've installed a few whole house solar applications in recent years and I just took the average kW usage and then sized the panels, inverter and battery bank accordingly. Unfortunately, I've never had the opportunity to measure and/or calculate the only load as a fridge.

2) Your cabin in the woods sounds like a nice idea.

3) My background on generators is very limited. I've installed a few whole house standby Generac's but I've never explored the inner workings of a genny. Since the Honda has an electric starter, a combination of a timer and relay can most likely be connected to accomplish your goal. But you would need to find a gen technician who is intimate with the inner workings of the Honda.

Customer: replied 1 year ago.
Actually all i would need is a honda repair manual. The start up is probably simple. (Lots of assumptions here ha ha )
They probably have an internal battery and a relay to the starter. If i can identify the relay control circuit I can just tap into it.
The shut down would be a little more work. It probably shuts of the ignition and might do it in an integrated circuit. has several add on products for Honda's. He takes them apart and installs starter motors on the 2000 watt non electric start models. Demonstrates the whole thing on video. has remote control stat and stop also.
Expert:  Kevin replied 1 year ago.

Yes, but keep in mind that if the generator is altered in any manner, this will void the warranty.

Customer: replied 1 year ago.
I can live with that.
Check out his site. he makes nice products. Has them professionally manufactured.Here's another guy makes a nice evap coolers for mobile use. He has changed his equipment recently. He used to have a separate timer unit to set how long the pump ran. a thought. If you figured out how to remote trigger start a Honda and trigger the shut off based on demand you would have product to sell. When I first started planning this truck, I looked into doing more with deep cycles. I later decided not to because of all this hassle. But the commissary fee has brought me back to it.When I was searching previously, I came across a number of people looking for ways to remote or trigger start a genny.
Some just want the simplicity of not having to open the genny box (like in a motorhome) but others want it to trigger off a load.Panellas addresses the first case, but not the second, and you might even be able to buy components from him and make a product to handle the trigger start. He already has the hookup to control the genny and he connects to a wireless control. . You would just have to connect to a different device.He's getting $300-$400 for his product. You could probably get the same
Expert:  Kevin replied 1 year ago.

Honda manufactures a remote starter for the EM7000is model. See link shown below:

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.


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