Powering multiple equipment with an inverter

[nob4uask]

Morning everyone,

Let me start by saying “nice little forum you have”, I look forward to browsing it more and learning from it.  I have a little issue which required me to think outside the box and found you while searching so I hope you can help.  My knowledge on this whole matter is below amateur but then again so was my understanding of overloading circuits and stuff 6 months ago, which is the time we started running a food stall.  Below is an explanation of what I am trying to do and all the information that is needed.  It is quite long and winded so please be patient.

We run a Mexican food stall at local markets and would like to use ALL of the following equipment which is 240v with 10a plugs.  There are a couple of smaller things such as a cash register & lights but nothing worth listing.

Hot Bain Marie –      1500w      7a
Cold Bain Marie –      150w      1a
Sandwich Press –    1800w      8a
Hot Dog Grill –            1400w      6a
Pie Warmer –       1400w      6a

Total                 6250w             28a


I rounded the amps up and it might drop it down about 1 but as you can see there is quite a bit of power consumption.  Also, keep in mind that this is maximum load during start up and they are commercial which are very efficient.  Once at operating temperature these devices only turn on a couple of times an hour for a couple of minutes to get back to desired temperature.  This of course would depend on outside temp & usage.

At a regular market we can have 2 and sometimes 3 10a power leads going to 3 different outlets but at our major market we just started we are only allowed 1 10a outlet.  I have removed some of the equipment and only use half of the heating on some to accommodate the allowed power.  But then came up with the crazy idea of maybe using an inverter with a battery to supply power to some of the devices.  I did some research and this is what I came up with.

I would run the cold bain marie, sandwich press & the misc equipment off of the supplied 10a power outlet.  That would leave me the rest of the equipment that totals about 4300w and 19a.  I would get each device to operating temperature with the outlet supplied then switch it to the inverter.  If my research and math is correct that would require me to have a 12v battery with 360ah or a 24v battery with 180ah.  These devices would need to run for about 2 hours over a 10 hour period which would put me at a whopping 720ah or 360ah batteries. 

I'm sure that there is a lot that I am missing and don't understand so I hope that everyone will be able to assist me in this little project.  Now to the questions,

Is this out of the realm of possibility?

Since the sandwich press won't be drawing power off the main outlet all the time can I have a battery charger plugged in and recharging the batteries over the 10 hour period?

Is there a device that I can plug the 2 power strips in for the 2 separate banks of devices which, depending on the load, will use either the provided power outlet or the inverter & batteries?  (I can clarify this if needed)

Back to the battery charger and per the above question.  Is there a device that I can plug the sandwich press and battery charger into where if the sandwich press isn't drawing power the battery charger is charger but once the press needs to reheat it switches the power to that so as not to overload the circuit?  (I can clarify this if needed)

How do I connect batteries together and what ways are there?  (I have read a little about it and am aware that these need to be deep cycle batteries)

The only 24v batteries I could find are some maH batteries, does 24v refer to a battery pack?

That about covers it and I appreciate everyone's time in advance.  I know that this will probably be a bit pricey but can probably make it up after a week or two.

[birdhouse]

interesting problem. 

it sounds like you could make things work without the battery and inverter.  sure you could go this route, but batteries are heavy, don't last forever, make a mess if acid gets out of them, and would have to be wired and de-wired each time they were set up.  another thing about batteries, is if you draw them close to dead on a regular basis, they won't last long.  a general rule to make batts last a reasonable amount of time, is to never draw more than 50% from them.  drawing even less per use will make them last even longer. 

i'm thinking of some sort of a timer, relay or programmed system where your loads are prioritized.  IE: a system where only one large load is turned on at a time.  imagine a clone of yourself constantly plugging in and unplugging loads at a fairly fast rate to keep the temps at the sweet spot per appliance while keeping the overall draw at less than 10A. 

i'm far from the right person to design or build the unit that could accomplish the above idea, but i know one could be made.  it sounds like you have enough power if you could send it to exactly the right place at exactly the right time for exactly the correct amount of time.

another option would be to use all 10A to charge a smallish batt bank with an inverter attached.  the problem here is there are significant losses both in making DC from AC, as well as turning the newly produced DC back into AC.  i'm guessing these losses wouldn't outweigh the gains of having a battery "buffer" for the times where all the large loads need juice at the same time.   

adam

[tanner0441]

Hi

If you are pulling 10 A on 240 V you are going to be pulling over 240 A  from your battery at 24 V. A battery setup that would handle that sort of load would need a truck to move it around, plus have you considered how thick the cable is going to be.  What are the objections to running a generator.

Brian.

[nob4uask]

Morning Adam & Brian,

Thanx for the response,

Adam - That's not a bad idea in regards to a controller that would prioritize the equipment, have any idea where I might go to have someone do something like this?  I think that I will do a test today of a two peaces of equipment to see if they have to turn on to reheat if it is at max load or dependent upon how much under the target temperature they have dropped under.  If I have it set at say 75c once it drops under that temp it will turn on to heat it back up, I am curious if it is a small load or max load to accomplish this.

Brian - I wasn't sure about my math but did indicate that they would not be running constantly only for a short period of time during reheating.  I came up with a 12v battery that would need to have about 720 aH for the 10 hours at the market.  I ran into a battery pack that runs 816aH called "APC Replacement Battery Cartridge #11", I wasn't sure if I could add the link but a quick search takes you to the page.  Is my math off or something?

Thanx both for your response, this is a nice site and I will be around probably asking more questions than answering them due to my knowledge of the subject.  I think the knowledge of being able to create and use power if needed is a great thing.

[Mary B]

10 minutes on off the rest of the hour an 800amp hour battery may work. I have a 24 volt 926 amp hour battery setup, 1,200 pounds and about a 4 foot by 6 foot space needed for them.

[birdhouse]

have any idea where I might go to have someone do something like this?

i'm sure there are folks on this site capable of building such a unit.  there's a very keen aussie on here that may show interest.  keep this thread alive, and someone may take a stab at it.  i'm guessing it would involve a picaxe or similar type of chip with custom programming to control four different relays.  or some solid state switches of sorts. 

from your original question, it sounds like you were already planning on putting more than a couple thousand dollars into the battery based solution, so i think your potential budget for a custom one off power controller could be feasible. 

an inverter capable of 6000+ watts alone would be in the thousands of dollars range. 


i just thought of another idea...  i'm guessing the equipment will draw close to full load even on the re-heat use, just for shorter bursts of time.  if you could have the heater "thermostats" reconfigured so they used PWM (pulse width modulation) they could draw far less, for for longer durations to maintain the desired temperatures. 

adam

[nob4uask]

10 minutes on off the rest of the hour an 800amp hour battery may work. I have a 24 volt 926 amp hour battery setup, 1,200 pounds and about a 4 foot by 6 foot space needed for them.

Arvo MaryAlana,

Thanx for that, I am starting to get a clearer picture in my head of how this could work with everyone's help and some tweaks.  I am kind of confused about whether I am looking at the right batteries or not.  Just for quick reference I went to ebay to check see approximate prices and I am concerned about the "you get what you pay for" quote.  I found a 220AH 12v AGM battery for $345.  If I connect 4 together I would have about 880AH with the dimensions of 1.88ft by 3.14ft with a weight of about 530lbs. 

Am I looking at the right batteries ? 

I know that the space and weight might change a little because of other equipment and all but didn't think that much.

[nob4uask]

have any idea where I might go to have someone do something like this?

i'm sure there are folks on this site capable of building such a unit.  there's a very keen aussie on here that may show interest.  keep this thread alive, and someone may take a stab at it.  i'm guessing it would involve a picaxe or similar type of chip with custom programming to control four different relays.  or some solid state switches of sorts. 

from your original question, it sounds like you were already planning on putting more than a couple thousand dollars into the battery based solution, so i think your potential budget for a custom one off power controller could be feasible. 

an inverter capable of 6000+ watts alone would be in the thousands of dollars range. 


i just thought of another idea...  i'm guessing the equipment will draw close to full load even on the re-heat use, just for shorter bursts of time.  if you could have the heater "thermostats" reconfigured so they used PWM (pulse width modulation) they could draw far less, for for longer durations to maintain the desired temperatures. 

adam

Arvo adam,

I like the input I have received and am starting to work on a diagram of what I would like so when the "aussie" comes on they might be able to help me.

If you subtract the 2400w that is supplied from the power outlet then I would only need to have an inverter that would pull in the range of 4300w.  I have found another pie warmer that only takes 850w so that saves me about 550 more plus I will only run half of the hotdog grill which will save me another 700w.  This puts me needed about 3100w worse case scenario such as all 3 devices came on at the same time.  I found a gen-power 3000w/6000w 12v/240v inverter on ebay for $360.  Am I looking at the right thing or as mentioned to MaryAlana, "you get what you pay for".

In regards to the PWM, which I have never heard of, I had thought several months ago if there was something that would reduce the amount of power going to a device which in turn would do what you said and that is a longer reheat time.  Didn't know where to go with it but now I know what to look for.  I don't think that I would want someone messing with the thermostats but instead look for something to plug into it that would reduce the power to it.

We have our first catering job this wed and then Chatswood Mall Markets thur & fri so I will be checking in and posting at weird times but really appreciate your help.  I can't wait to get into actually building a wind or solar system now.

As far as the money goes, not that rich but after looking at prices of inverters & batteries I kind of got a ball park figure.

Once again, thanx for your time.

[Mary B]

A smaller generator would be a heck of a lot less work... and cheaper. Those dirt cheap ebay inverters are junk

[nob4uask]

A smaller generator would be a heck of a lot less work... and cheaper. Those dirt cheap ebay inverters are junk

Unfortunately a generator isn't an option.  Could you please point me in the right direction in regards to where to get reasonably priced inverters & batteries.

[Frank S]

Is this to be a permanent stall or a mobile cart or trailer unit?
 if a mobile unit such as an enclosed trailer I would think it may be about 2.4m by 3.5m  if so and it were parked under blue sky then an array of solar mounted on the roof could help. you could get nearly 1800w s of use-able energy.
 Of course that would be moot if parked under roof.
 you might type in the word induction  in front of your appliances  Induction appliances require less energy over all to use.
 
 Also I didn't notice any mention of a fridge for chilled storage.
  The last time I visited down under I heard talk in some areas of adopting the UK 13 & 15 amp sockets this was in 2010

[nob4uask]

Is this to be a permanent stall or a mobile cart or trailer unit?
 if a mobile unit such as an enclosed trailer I would think it may be about 2.4m by 3.5m  if so and it were parked under blue sky then an array of solar mounted on the roof could help. you could get nearly 1800w s of use-able energy.
 Of course that would be moot if parked under roof.
 you might type in the word induction  in front of your appliances  Induction appliances require less energy over all to use.
 
 Also I didn't notice any mention of a fridge for chilled storage.
  The last time I visited down under I heard talk in some areas of adopting the UK 13 & 15 amp sockets this was in 2010

Morning Frank,

Thanx for the response.

It is a 3x3m Gazebo stall so a lot of loading and unloading.  The markets are on Thurs & Fri so we leave the Gazebo there overnight and take any expensive equipment with us.  A lot of lifting and getting old... 

Australia is a little behind on things and from what I understand that includes the power situation.  15a outlets are around but from what I have seen it is the exception not the rule.  Six months ago I wouldn't of even known what you where talking about..lol

I don't think induction appliances will help us in this situation, we use an LPG grill for heating.  Simple system, quick heating and no power needed.  We where hoping to use a small 2 burning grill kind of like a chaffing dish to keep the food warm but the temp control is an issue and I really don't have time to get into that project right now.  This would at least remove another 1500 or so watts from my needs.

[OperaHouse]

That would be a nice little project for an Arduino UNO.   Every device would have a demand request and schedule priority.  It would know what current every device used and have a load and unload schedule.  I imagine everything could run and you wouldn't even notice it was happening. 

[DamonHD]

Yes, an Arduino (eg UNO or Mega) or a PICAXE or similar could be just the job...

Rgds

Damon

[Mary B]

When I was catering BBQ I used a propane steam table system.... to many places I set up had zero power and no generator allowed(middle of parks etc). Worked well and didn't use that much gas once it was up to temp.

http://www.bigjohngrills.com/CWS.html

[tanner0441]

Hi

If your looking at a programmable controller I would also look at soft start capability so you are not going to suddenly drop a massive load on the inverter. If  you have LPG for the grill are there any of your appliances that you could use LPG for heated food storage, as Frank said chillers, freezers, could also be LPG. serve over heated counters could be radiant LPG, hot water could be on on demand LPG.

I think a serious re think and planning exercise are called for. You have to plan for the worst case scenario plus at least 50%.

Brian.

[nob4uask]

Thanx everyone for the great help, with that and some research on my own I will throw out what I came up with.

OP indicated that I needed about 6250w and am only allowed 2400w.  I can reduce it by doing the following.

Hot Bain Marie - MaryAlana's link was perfect but need to find something like that here or get it shipped.  I would have to do conversions but I am assuming that gastronorm pans are universal.

Cold Bain Marie - 150w
Sandwich Press - 1800w (I have checked but this will be tough to beat)
Hot Dog Grill - 700w (We will only use the front heating elements but found a nice commercial one that is more efficient but pricey)
Pie Warmer - 850w (We will replace the current one we have with a smaller unit)

Misc Equipment - 250w

Total needed - 3750w
Allowed -         2400w

Difference      -1350w

With the new numbers and the info this can probably be accomplished with a priority controller like those mentioned and a small inverter/ battery pack backup.  I searched and read about the Arduino (eg UNO or Mega) & PICAXE but that is way our of my realm of knowledge so if anyone knows where to go from here in regards to that please let me know.

On a few side notes;

Our worst case scenario is an LPG grill.  It can do it all just takes longer and with workers wanting lunch it can become a nightmare.
We use a Coleman "Water on demand" system that runs off battery and propane, not an issue.
I don't need chilling or freezer because of ice chests/ eskies and the bar fridge we could take is about 150w so not to relevant. 

Once again thank you for your time and have a nice day wherever you are.

[OperaHouse]

The utilites are certainly no stranger to load shedding. Most people think the smart grid is just a scam to raise their electric
bill but at some point appliances will begin to communicate to reduce peak demand.  In the 70's Vermont was installing timers on
water heaters to reduce demand.  I just installed a NYLE heat pump on my electric water heater.  Utility companies have written
up more than a dozen papers on their energy savings.  Each of these highlight a reduction in peak time demand of 2KW in the morning
and evening. If the units were less expensive, the utilities would be giving them away.  The following would be a basic concept for
load sharing that wouls not be expensive at all. A UNO can be had for $10, a four chanel relay board is $6 and current sensor is $3.


For the simplest example there are ten devices.  Those devices are placed in six groups.  Each group adds up to 10A total.
One or more of the same high use devices might be placed in eqach group.  Those devices with lower priority/useoccur in
groups less often.  Each group will operate for three minutes and there will be six groups.  A relay for each device only
interrupts the heating element.  Motors and temperature controllers are kept alive.

This gives twenty group cycles each hour and will likely give the appearance of normal operation without ever goung over 10A.
The next step up would be to include a total current sensor.  The basic group would still add up to 10A but there would be
two or three "alternates" that could be added depending upon demand.  If current demand was 6A another 3A device could be added.
If no added current was detected, a second alternative load would be substituteed for the first.  New loads would be added at
ten second intervals.  However, if a new load were sensed from the basic group the alternative device would be turned off within
a second. The basic operation of breakers is thermal with a time delay.  Short duration loads over 10A would not cause a breaker
trip.

It would not be a complicated program.  The currents are relatively low allowing the relays to be small and low cost.  Initially
it would take a lot of monitoring to get the groups right because little is known about the demand cycles of the devices.  The UNO
laptop monitoring would make that easy and group changes could be made quickly.

[Mary B]

Replace that front opening fridge with a chest freezer with an outboard temp controller, much higher efficiency

[nob4uask]

The utilites are certainly no stranger to load shedding. Most people think the smart grid is just a scam to raise their electric
bill but at some point appliances will begin to communicate to reduce peak demand.  In the 70's Vermont was installing timers on
water heaters to reduce demand.  I just installed a NYLE heat pump on my electric water heater.  Utility companies have written
up more than a dozen papers on their energy savings.  Each of these highlight a reduction in peak time demand of 2KW in the morning
and evening. If the units were less expensive, the utilities would be giving them away.  The following would be a basic concept for
load sharing that wouls not be expensive at all. A UNO can be had for $10, a four chanel relay board is $6 and current sensor is $3.


For the simplest example there are ten devices.  Those devices are placed in six groups.  Each group adds up to 10A total.
One or more of the same high use devices might be placed in eqach group.  Those devices with lower priority/useoccur in
groups less often.  Each group will operate for three minutes and there will be six groups.  A relay for each device only
interrupts the heating element.  Motors and temperature controllers are kept alive.

This gives twenty group cycles each hour and will likely give the appearance of normal operation without ever goung over 10A.
The next step up would be to include a total current sensor.  The basic group would still add up to 10A but there would be
two or three "alternates" that could be added depending upon demand.  If current demand was 6A another 3A device could be added.
If no added current was detected, a second alternative load would be substituteed for the first.  New loads would be added at
ten second intervals.  However, if a new load were sensed from the basic group the alternative device would be turned off within
a second. The basic operation of breakers is thermal with a time delay.  Short duration loads over 10A would not cause a breaker
trip.

It would not be a complicated program.  The currents are relatively low allowing the relays to be small and low cost.  Initially
it would take a lot of monitoring to get the groups right because little is known about the demand cycles of the devices.  The UNO
laptop monitoring would make that easy and group changes could be made quickly.

Morning Opera,

I am really hoping that you are in Sydney with that user name to make things easier.

I understand what you are saying but don't even know where to start, please provide more info.

[OperaHouse]

No, named for the opera house on Nantucket. It's glorified now but it was probably no more than a brothel.

There are no simple solutions.  Each one requires at least some ability to deduce.  Most heating devices are likely run at a 50% duty cycle.  One possible solution would be to reduce the voltage to them with a transformer.  A 240V/ 48V wired as a buck might allow all the heaters to work at the same time.  This solution would only work with temperature controls that were mechanical.

I would be the last one to say you couldn't get into a pack of trouble with a UNO.  There are variations of code that are almost unreadable to me.  However, most of the things people do with these fall into the realm of conversational English.   The code would go in a straight line, simple output and delay stuff.  The compiler is FREE and you can try and write a program and compile it with error checking before you ever buy anything.  They are unforgiving as far as spelling, comas, brackets and the like.  Many non technical people in various hobbies have figured them out.  If you can get it downloaded into your laptop, you are 70% there.

[nob4uask]

Appreciate the info Opera but don't understand the link between all of this.  I don't have a problem coding because I was in the business when I was younger but don't I need some hardware somewhere along the way?