Inverters, bike charging and other power questions.

[goneoff]

I have two 130ah AGM batteries and 350w of solar on the roof. I understand inverters are not the best for 12v wet batteries however we have just purchased a couple of e-bikes that will need charging when we are away both their ratings are attached.

Questions are:-

1. What’s the smallest inverter I would have to buy to charge both bikes up simultaneously?
2. Would a PSW inverter be more efficient than a MSW inverter?
3. If I decided to purchase an inverter to power our small 800w microwave say a 1500w PSW would that be a heavier draw on my batteries than the small inverter when purely charging the bikes?

I know a lot of questions but the main issue is changing the bikes although if I can buy an inverter that can run the microwave on rare occasions without compromising the batteries I will buy a larger inverter. Hope that makes some sense. Thank you

 

[pappajohn]

The bikes (combined) will draw 46amps per hour from the batteries
The microwave is more difficult as the stated 800watt is the microwave output but a 1500watt inverter will draw 125amps at full power. Once the oven has started the amps will drop, they have a high startup current.
On top of that inverters are around 90% efficient so there will be some conversion losses.

 

[jonasw19]

For the bikes pure sine wave
42x3=126watts
42x2=84 watts
Total =210watts
Allow 250 to 300watts to allow for inefficiency.

If you run a 1500watt inverter then it will have a greater offload draw than a 300watt .
All the above assume the properly sized 12v cables

 

[Richard n Ann]

Input is 2 amps at 230v so 500w each

Inverter 1000w minimum

 

[pappajohn]

For the bikes pure sine wave
42x3=126watts
42x2=84 watts
Total =210watts
Allow 250 to 300watts to allow for inefficiency.

If you run a 1500watt inverter then it will have a greater offload draw than a 300watt .
All the above assume the properly sized 12v cables

That's the output watts from the charger at 230vac.
The OP is looking for the inverter input battery draw

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[jonasw19]

The relevant figures are the output ones, if you use the input ones and compare to the output then than would imply a very poor efficiency.
Output from data plates are 126watts and 84 watts, total 210 watts approx 20amps at 12volts

 

[ToBoldlyGo]

I find the dialogue about input vs output watts difficult, ending my electrical knowledge at O level. I see it says 'max' against the input current, does that have a bearing?

 

[royw]

It is the input values you need to use ( I am an electronic engineer formally qualified - people talking output loads are talking rubbish - sorry) If you are plugging a device in to a source of power i.e inverter you need to deal with the devices supply needs not what device supplies. If you under spec the inverter you will most probable get nothing out as it will overload or worst cause damage. Additionally the ambient draw of a large or small inverter wont be different and the current it will draw will be on demand so fitting a larger one is only really a cost decision, if you never choose to load it it wont ever draw excessive current. So in short you are better over than under spec'ing this. Now if you find devices dont work properly due to modified then again you will regret the decision to go cheap so just go pure in the first place. Now on the point of microwaves you have quite a draw with these and yes your batteries will cope but not for long, then of course you need to replenish and after that consider how many cycles of deepdraw your batteries are happy to take. Your other option if you are just thinking of bikes is to use dedicated chargers that take the 12 volt supply they will ultimately provide less load to your batteries i cannot remember url but they do chargers for wheelchairs etc

 

[jonasw19]

I am surprised that the input MAX load of the thick end of 450watts per charger, is the determining factor as the energy required as per the output of the charger 42v at 3amps would seem to be the more relevant or the charger is hopelessly inefficient, converting 450watts input to 126 watts output 50% efficiency.
As a data point I run 1x2a and 1x4a 42v output chargers for my ebikes, simultaneously, from a 300w psw inverter with no problems and the battery monitor shows a max 20amp draw.
The reason for the apparent discrepancy may lie in the data plate saying input MAX current at a lower voltage of 110v as evidenced by the second data plate. This shows a multi voltage input feeding to a single voltage output.

 

[royw]

I am surprised that the input MAX load of the thick end of 450watts per charger, is the determining factor as the energy required as per the output of the charger 42v at 3amps would seem to be the more relevant or the charger is hopelessly inefficient, converting 450watts input to 126 watts output 50% efficiency.
As a data point I run 1x2a and 1x4a 42v output chargers for my ebikes, simultaneously, from a 300w psw inverter with no problems and the battery monitor shows a max 20amp draw.
The reason for the apparent discrepancy may lie in the data plate saying input MAX current at a lower voltage of 110v as evidenced by the second data plate. This shows a multi voltage input feeding to a single voltage output.

Their data plate may be wrong or being on the cautious side but regardless the value you take is the input requirements on the chargers.

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[Lucky]

If I've followed this correctly, the answer to "Charging Electric Bikes, the Ultimate Question of Life, and Everything" is 42, calculated by an enormous supercomputer named Deep Thought over a period of 7.5 million years. Unfortunately, no one understands what the question is.

 

[royw]

If I've followed this correctly, the answer to "Charging Electric Bikes, the Ultimate Question of Life, and Everything" is 42, calculated by an enormous supercomputer named Deep Thought over a period of 7.5 million years. Unfortunately, no one understands what the question is.

I answered your question, its not for debate, you calculate the supply voltage * current you need to add some latitude for tolerance. As I said PSW is a preferred optionto MSW as some devices can operate incorrectly with MSW so for the price difference i Would go MSW I am qualified to repair anything fom a white goods or TV videons to avionics systems on modern fighter jets nowadays selling IT systems to the largest organisations accross the globe, choose to take the advice or not.

 

[Lucky]

 

[Tombola]

So tell me again, how good you are sparks

 

[royw]

So tell me again, how good you are sparks

I can put a battery in a remote control the right way 50% of the time.

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[royw]

http://powatechnic.com/?SID=bb0e6cde2ac1bf47806948758a6b4e41 charger for 12 v supply no invertor needed

 

[royw]

 

[cmcardle75]

It is the input values you need to use ( I am an electronic engineer formally qualified - people talking output loads are talking rubbish - sorry) If you are plugging a device in to a source of power i.e inverter you need to deal with the devices supply needs not what device supplies. If you under spec the inverter you will most probable get nothing out as it will overload or worst cause damage. Additionally the ambient draw of a large or small inverter wont be different and the current it will draw will be on demand so fitting a larger one is only really a cost decision, if you never choose to load it it wont ever draw excessive current. So in short you are better over than under spec'ing this. Now if you find devices dont work properly due to modified then again you will regret the decision to go cheap so just go pure in the first place. Now on the point of microwaves you have quite a draw with these and yes your batteries will cope but not for long, then of course you need to replenish and after that consider how many cycles of deepdraw your batteries are happy to take. Your other option if you are just thinking of bikes is to use dedicated chargers that take the 12 volt supply they will ultimately provide less load to your batteries i cannot remember url but they do chargers for wheelchairs etc

I am also a qualified electronic engineer. However, I must disagree with your opening statement. Input ratings for power supplies are normally a load of balls. Typically they give input currents far in excess of what is actually drawn. Output ratings suitably adjusted for likely efficiency are normally far more reliable for actual loadings.

For example, the first power supply I looked at sitting in front of me is rated input: 100-240V 1.8A (max) and the output is 12V, 5A. This PSU is capable of providing up to 60W. Using the minimum input voltage, that input rating is 180W. I can assure you, that if this small plastic cased power supply was supplying the full 60W and, hence, dissipating 120W, my house would be on fire and I wouldn't be writing this message. The house, however, is not on fire, and the power supply box is only very slightly warmer than its surroundings.

I also disagree that the quiescent power of a large inverter and a small inverter are the same. A 150W inverter not actually supplying a load will typically draw far less current than a 3kW inverter also not supply anything. They may have similar efficiencies at their rating load, but at low loads, the smaller inverter will win every time.

 

[Richard n Ann]

Input ratings for power supplies are normally a load of balls. Typically they give input currents far in excess of what is actually drawn. Output ratings suitably adjusted for likely efficiency are normally far more reliable for actual loadings.

That's very probably true but it's down to the op how much he wants to risk it.

I also disagree that the quiescent power of a large inverter and a small inverter are the same. A 150W inverter not actually supplying a load will typically draw far less current than a 3kW inverter also not supply anything. They may have similar efficiencies at their rating load, but at low loads, the smaller inverter will win every time.

Definitely true, our little PSW 200w inverter takes 0.2amps
I'm also qualified, City & Guilds level 3, mind you I've forgotten most of it

Lenny HB autorouter what are your thoughts on this?

 

[royw]

That's very probably true but it's down to the op how much he wants to risk it.



Definitely true, our little PSW 200w inverter takes 0.2amps
I'm also qualified, City & Guilds level 3, mind you I've forgotten most of it

Lenny HB autorouter what are your thoughts on this?

The validity of the manufacturers label i cannot vouch for but it is still that load you should use for calculation and not the devices output. My point on sizing stands in that higher spec is better than lower, the quiescent draw on a quality inverter is not that greater, Agree you can choose to have multiple inverters for different tasks. I believe the OP was talking 1.5kw versus say .6 kw (for bike chargers) appreciate your C&G level obtained - congratulations. woop woop. Power calcs are within the grasp of anyone common sense appears a scarce commodity .. Under spec at your own risk.

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[Jo662]

I have two 130ah AGM batteries and 350w of solar on the roof. I understand inverters are not the best for 12v wet batteries however we have just purchased a couple of e-bikes that will need charging when we are away both their ratings are attached.

Questions are:-View attachment 478172View attachment 478174

1. What’s the smallest inverter I would have to buy to charge both bikes up simultaneously?
2. Would a PSW inverter be more efficient than a MSW inverter?
3. If I decided to purchase an inverter to power our small 800w microwave say a 1500w PSW would that be a heavier draw on my batteries than the small inverter when purely charging the bikes?

I know a lot of questions but the main issue is changing the bikes although if I can buy an inverter that can run the microwave on rare occasions without compromising the batteries I will buy a larger inverter. Hope that makes some sense. Thank you

What about this option!

Thread 'Been thinking about fitting an inverter,but.....'
https://www.motorhomefun.co.uk/forum/threads/been-thinking-about-fitting-an-inverter-but.234149/

 

[royw]

What about this option

Thread 'Been thinking about fitting an inverter,but.....'
https://www.motorhomefun.co.uk/forum/threads/been-thinking-about-fitting-an-inverter-but.234149/

https://poweroak.nl/fr/powerbanks/1...00wh-solar-ac-dc-generator-8719324080583.html is another one, they do seem quite nice and self contained.

 

[Neilfg]

When I wanted to size up an inverter for use in the van I ran the devices at home on mains using a small power monitor, very cheap. This shows the amps and wattage used by the device. This gave me piece of mind and showed that calculated draw never matched the actual draw. The debate about power draw calculated from labels make me laugh as it is all academic the only way to be precise is to measure it especially bike chargers and coffee machines.

In your case to be safe I would get at least an 1000w PSW and maybe 1200w.

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[goneoff]

When I wanted to size up an inverter for use in the van I ran the devices at home on mains using a small power monitor, very cheap. This shows the amps and wattage used by the device. This gave me piece of mind and showed that calculated draw never matched the actual draw. The debate about power draw calculated from labels make me laugh as it is all academic the only way to be precise is to measure it especially bike chargers and coffee machines.

In your case to be safe I would get at least an 1000w PSW and maybe 1200w.

Energenie ENER007 Energy Saving Power Meter Socket

Order online at Screwfix.com. Monitor and measure the energy use and costs of running your household appliances. Simply plug into a powered mains socket and then plug any 13 amp-rated appliance in. Discover which appliances use most energy, helping you lower power bills and reduce emissions...

www.screwfix.com

http://

When I wanted to size up an inverter for use in the van I ran the devices at home on mains using a small power monitor, very cheap. This shows the amps and wattage used by the device. This gave me piece of mind and showed that calculated draw never matched the actual draw. The debate about power draw calculated from labels make me laugh as it is all academic the only way to be precise is to measure it especially bike chargers and coffee machines.

In your case to be safe I would get at least an 1000w PSW and maybe 1200w.

Energenie ENER007 Energy Saving Power Meter Socket - Screwfix

Order online at Screwfix.com. Monitor and measure the energy use and costs of running household appliances. Simply plug into a powered mains socket and then plug any 13A rated appliance in. Discover which appliances use most energy, helping you lower power bills and reduce emissions. FREE next...

www.screwfix.com

Many thanks for the clarity. I clearly understand the requirement for measurement in order to size an inverter correctly, however having said that in your opinion are you saying that a 1200w inverter would charge up both my bike batteries simultaneously or my 800w microwave occasionally?

 

[Neilfg]

Many thanks for the clarity. I clearly understand the requirement for measurement in order to size an inverter correctly, however having said that in your opinion are you saying that a 1200w inverter would charge up both my bike batteries simultaneously or my 800w microwave occasionally?

I have 2 ebikes and was surprised at how low the draw was in reality compared to the calculated input figures. My 1000w PSW Inverter works well and is perfect for topping up both ebikes when needed (also a bread maker monitor really helped here) , I have about 160ah batteries total.

I have no experience of a microwave in a van but if it says 800w a 1000w inverter should be fine ( monitor will confirm). I only suggested 1200w as although bigger than required it is sometimes more efficient. I found previously that an inverter working close to it limits was noisy and not as efficient. When I was looking it was an option as a good range available and not that much bigger. As it was I found a 1000w that fitted in neatly and at the right price.

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[cmcardle75]

I have 2 ebikes and was surprised at how low the draw was in reality compared to the calculated input figures. My 1000w PSW Inverter works well and is perfect for topping up both ebikes when needed (also a bread maker monitor really helped here) , I have about 160ah batteries total.

I have no experience of a microwave in a van but if it says 800w a 1000w inverter should be fine ( monitor will confirm). I only suggested 1200w as although bigger than required it is sometimes more efficient. I found previously that an inverter working close to it limits was noisy and not as efficient. When I was looking it was an option as a good range available and not that much bigger. As it was I found a 1000w that fitted in neatly and at the right price.

Remember that microwaves are sold by output power and aren't anywhere near 100% efficient, so input power is significantly more, often with large inrush currents.

 

[Neilfg]

Remember that microwaves are sold by output power and aren't anywhere near 100% efficient, so input power is significantly more, often with large inrush currents.

Hence why it might be wise to use a monitor

 

[Jo662]

https://poweroak.nl/fr/powerbanks/1...00wh-solar-ac-dc-generator-8719324080583.html is another one, they do seem quite nice and self contained.

The reason I went for the EcoFlow was the time it takes to charge, which is about hour and a half from flat. We're as the poweroak can take anything up to 8 hours from flat.

 

[royw]

The reason I went for the EcoFlow was the time it takes to charge, which is about hour and a half from flat. We're as the poweroak can take anything up to 8 hours from flat.

That is really good, how do the capacities compare ?

 

[Lenny HB]

I am also a qualified electronic engineer. However, I must disagree with your opening statement. Input ratings for power supplies are normally a load of balls. Typically they give input currents far in excess of what is actually drawn. Output ratings suitably adjusted for likely efficiency are normally far more reliable for actual loadings.

Generally yes but our Bosch e-bike chargers are rated at 1.5 amps at 230 volts and thats what they take, when running from the inverter the 12v current draw is over 30 amps.

I also disagree that the quiescent power of a large inverter and a small inverter are the same. A 150W inverter not actually supplying a load will typically draw far less current than a 3kW inverter also not supply anything. They may have similar efficiencies at their rating load, but at low loads, the smaller inverter will win every time.

Yep, our 1000w inverter draws 2 amps with no load.

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