Induction hob power draw question

[Epic-Rob]

OK so I have been doing some experimenting with induction cooking v gas, as in my next build I am thinking I want to be just induction. But I am getting some weird readings that I am not really sure how to interpret and possibly my Lithium batteries aren’t as good a quality as others.

The system

2x 100Ah LiFePO4
1 x 2500w pure sine wave inverter
1x 2000w single Westinghouse induction cooktop
1 x voltronic shunt meter.

160W solar on roof though PWM controller, this is what is built into the NDS DC-DC charger, but this doesn’t really factor in to the testing. If I have fridge on I get a negative over 24 hr so deff need a bit more solar and MPPT controller on next build. DC-DC charger saves the day the

The Test
OK so I start off at full 200Ah as indicated on shunt, fill kettle and put on induction at full 2000w, leave on for 3mins
Draw is indicated (on shunt) at 162-165 amps and at end shunt indicates 189Ah remaining (11Ah used).

Repeat test, same as above

Draw same as before and after 3 mins we now have 176Ah (13Ah used) in battery as indicated by shunt.


So if I do some maths (feel free to correct this if wrong)


Over the 6 mins it has drawn 24Ah (11 on tst 1 and 13 on tst2) from total of 200ah that is 12% of total capacity

On actual draw – 162amp /60secs = 2.7Ah/min x 6min = 16.2Ah that to me is now 8.1% of total capacity

So there is a diff of 8Ah somewhere!

When I have been away it seems to draw more as the battery gets lower. Other than looking at the shunt I don’t know how to do a secondary capacity test.

Watching a few youtube vids on this it seems that the draw of 162amp is about right but the amount it taking from battery seems excessive, hence my wondering if my batteries are a bit to ‘cheap’….. (have attached spec sheet of them) or maybe I just don’t have enough battery capacity

On my next build I have already built a battery from separate cells (230ah) with Dally BMS etc


So possible reasons.

• I just don’t have enough battery capacity
• Batteries are cheap!
• Note battery has max cont discharge of 100A so that could be an issue ?
• Could get smaller induction hob but then would just take longer to boil

So opinions please.


Seems Bryn23 has done something similar but he knows what he is doing

 

[drinfinity]

If you are drawing 62% more current than the battery is rated for, you could probably just put the kettle on top of the battery to make a brew.

 

[Loz]

…Jetboil… for the kettle as you are never going to get close to the transfer of energy from gas to water.

Induction will be fine for cooking where you need less energy over a longer period.

 

[Epic-Rob]

If you are drawing 62% more current than the battery is rated for, you could probably just put the kettle on top of the battery to make a brew.

OK so thats one of the problems max discharge of 100A and i am drawing 160A so those batteries arnt up to supplying that load.

 

[Epic-Rob]

…Jetboil… for the kettle as you are never going to get close to the transfer of energy from gas to water.

Induction will be fine for cooking where you need less energy over a longer period.

Sort of want to do away with having gas though. gas is a backup option but not 1st go to.

 

[Salty Spuds]

OK so thats one of the problems max discharge of 100A and i am drawing 160A so those batteries arnt up to supplying that load.

If you have 2 batteries in parallel both with 100A max draw, then you have a combined 200A max draw. The issue may be the difference in internal resistance of the batteries. If they aren’t matched then one battery will supply more than the other.

 

[DXX]

Sort of want to do away with having gas though. gas is a backup option but not 1st go to.

Wallas XC Duo, a fantastic bit of kit. Double hob and combined heater, costs next to nothing to run and maintenance free.

 

[paddy26]

If you have 2 batteries in parallel both with 100A max draw, then you have a combined 200A max draw. The issue may be the difference in internal resistance of the batteries. If they aren’t matched then one battery will supply more than the other.

Also, are the leads coming the batteries to your bus bar the same length, as otherwise the resistance in the wire could be a factor?

 

[PB-T6]

Hi
related question
would less power be used boiling say 1L water in a home kettle using the 240v van circuit.
or if 1L of water boiled in a induction friendly kettle on the hob. .?
an easy test and one I have been meaning to do.

we have 230amp ( max draw 200amps) arrangement and hob/microwave. And all is good.

 

[CJW]

Exactly where is your shunt in the wiring of this? Do you have a photo or a sketch?

Wiring shunts incorrectly is common and gives misleading results.

 

[Loz]

Hi
related question
would less power be used boiling say 1L water in a home kettle using the 240v van circuit.
or if 1L of water boiled in a induction friendly kettle on the hob. .?
an easy test and one I have been meaning to do.

we have 230amp ( max draw 200amps) arrangement and hob/microwave. And all is good.

It's the same power required, but the total used would be more on the battery>inverter>induction, due to the additional losses in the process of transforming the power.

 

[Linoleum Bonypart]

Would like to know how long an induction would take to boil compared to two minutes of jet boil

 

[Loz]

Would like to know how long an induction would take to boil compared to two minutes of jet boil

I can probably do that experiment.

 

[Linoleum Bonypart]

Cheers would prove something to people

 

[Epic-Rob]

If you have 2 batteries in parallel both with 100A max draw, then you have a combined 200A max draw. The issue may be the difference in internal resistance of the batteries. If they aren’t matched then one battery will supply more than the other.

both batteries identical - but could be something i need to check with next battery as its made of individual cells totaling 230Ah so maybe only 100Ah draw

 

[Epic-Rob]

Wallas XC Duo, a fantastic bit of kit. Double hob and combined heater, costs next to nothing to run and maintenance free.

considered that option but its the time it takes to heat up - want a brew in 2 mins not 10.

 

[Epic-Rob]

Also, are the leads coming the batteries to your bus bar the same length, as otherwise the resistance in the wire could be a factor?

Not sure i fully understand, but battery under each seat, its set up so power runs through batteries rather than been drawn off one, and connected together with thick cable

 

[Epic-Rob]

Hi
related question
would less power be used boiling say 1L water in a home kettle using the 240v van circuit.
or if 1L of water boiled in a induction friendly kettle on the hob. .?
an easy test and one I have been meaning to do.

we have 230amp ( max draw 200amps) arrangement and hob/microwave. And all is good.

seen you tube vid on this, kettle used as much amp but took longer to boil hence more total Ah used.

 

[Epic-Rob]

Exactly where is your shunt in the wiring of this? Do you have a photo or a sketch?

Wiring shunts incorrectly is common and gives misleading results.

shunt is directly next to the battery and was originally set up with help of loz amd Dell, so pretty confident the shunt readings are all good

 

[Epic-Rob]

Would like to know how long an induction would take to boil compared to two minutes of jet boil

yes but i am trying to get away from all the gas thing - i am sure it is nearly as quick to boil but by the time you have got it out of cupboard set it up etc i may as well just use a built in gas hob!