Help working out inverter requirements please

[RubyOptics]

Hi all,

I'm trying to work out the inverter requirements to charge a (possible) electric bike/scooter and just want to check my numbers!

On the charger it states the following :

Input - 100-240v, 50/60Hz 2.0A MAX
Output - 41v 1.7A

I think that this means I would need, at minimum a 500W PSW inverter? Can anyone with a bit more experience confirm please?

 

[tonyidle]

You could use a smaller inverter. Max 2.0A will be drawn when on 110V mains. However 500W makes it useful for other things too. If you wish to go smaller 300W will be OK.

 

[RubyOptics]

Maybe if I explain what I want to do in a bit more detail it would help somewhat! We don't really run any mains equipment in the van at all, with everything being either USB or gas right now.
We are considering buying a couple of folding E-bikes to give us a bit more "range" when we are parked up somewhere and fancy a bit of an explore. We currently have 350W solar running from an MPPT controller.
We would like to be able to charge a couple of ebikes in the garage either using power from our solar or from the alternator when driving. I'm looking for the best way to do this. I'm aware that ANY inverter is going to be wasteful and inefficient so would prefer to avoid it if I can. Is there a better way?

 

[Kannon Fodda]

It is the input rather than output that you need to be worrying about.

100V 2.0A Max is 200W
240V 2.0A Max is 480W

However that is a peak, probably as the charger kicks in and actual charge use will be less.

The output of 41V 1.7A is only 70W. So normal load once it's going is quite small.

I'm using a Victron 375VA inverter (300W output continuous 700W peak - a few seconds) for my Bosch e-bike, a slightly different charger at 36V output. That works fine.

What you really do need to watch is how much 12V battery capacity you have. My Bosch 500 battery, fully emptied, takes some 7 hours to recharge using the "compact" 2A charger. With the overhead from the inverter's inefficiency, that becomes a fair amount of 12V Ah consumption.

Use the inverter when driving along is great, alternator should recharge your leisure battery and keep up. If you have 350W solar that also gives a good recharge and on a moderate day you should be able to recover the drained capacity from leisure well within a day.

 

[RubyOptics]

It is the input rather than output that you need to be worrying about.

100V 2.0A Max is 200W
240V 2.0A Max is 480W

However that is a peak, probably as the charger kicks in and actual charge use will be less.

The output of 41V 1.7A is only 70W. So normal load once it's going is quite small.

I'm using a Victron 375VA inverter (300W output continuous 700W peak - a few seconds) for my Bosch e-bike, a slightly different charger at 36V output. That works fine.

What you really do need to watch is how much 12V battery capacity you have. My Bosch 500 battery, fully emptied, takes some 7 hours to recharge using the "compact" 2A charger. With the overhead from the inverter's inefficiency, that becomes a fair amount of 12V Ah consumption.

Use the inverter when driving along is great, alternator should recharge your leisure battery and keep up. If you have 350W solar that also gives a good recharge and on a moderate day you should be able to recover the drained capacity from leisure well within a day.

Thanks for the info. I had calculated using the input side of things as that seemed the logical way of working it out, but good to have it confirmed! You are right about the capacity issues, but we are fairly careful with our power usage anyway and I think that as long as we stick to a routine of 1 - lots of sun we can charge during the daylight hours, 2 - No sun we only charge when we are driving, 3 -If on hookup then rejoice, for we are in the promised lands!! then we should be ok!

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[autorouter]

I think that as long as we stick to a routine of 1 - lots of sun we can charge during the daylight hours, 2 - No sun we only charge when we are driving,

If you have good leisure battery capacity you have another option. Charge whenever you want, evening or overnight, from the leisure batteries. Refill the leisure batteries during the day from solar. This avoids the problem of charging during daylight when you want to be out biking.

Example: A 500 watt-hour battery is equivalent to 500/12 = 42 amp-hours at 12V. So two of these will have a total capacity of 84Ah. If you have 200Ah of leisure battery, then that's about 100Ah to avoid going below 50%. You'd have just about enough leisure battery capacity to cover that, with very little to spare. However if the ebike batteries were smaller (375Wh is common) or you had more leisure battery capacity, then this option would work.

Your 350W of solar should produce well over 100Ah, even on an average day, so the batteries would refill while you are out.

 

[RubyOptics]

Thanks autorouter, I'm still trying to figure out the best way of making this idea feasible. We currently have only 85AH fitted (although we are going to be doubling this fairly soon if we don't transition to lithium). The bike I am considering is the Himo Z20 folding E-bike which comes with a 36v, 10Ah battery. If I can at all avoid fitting an inverter I would prefer it to be honest with you. I have seen some chargers for E-bikes running from a cigarette lighter socket, which I assume are a 12-36v boost converter set-up. I know that this would take longer to charge but I still think this type of set-up would suit us better. Any thoughts?

 

[Raul]

If you can get boost charger from 12-36v you will save 5-7% of energy going in the battery. A victron inverter 250w will do the job at a efficiency of 90-97%. The boost chargers are not far off, in fact some are worse at 85-87%. So it does matter if is a cheap boost charger or we’ll built converter. Personally I would stick to a small victron inverter, no mater how you swing it, the energy going in the batteries needs to come from somewhere. At 370wh with the inverters 10% 37wh that’s 3ah of your battery, added if charged via inverter. This inverter inefficiency ppl talk about was long time ago with qassy and square wave. The new technology with high frequency switching fets producing a perfect sine wave, can be as efficient as 95%, we moved on from the myth a bit.

 

[autorouter]

The bike I am considering is the Himo Z20 folding E-bike which comes with a 36v, 10Ah battery.

Just to clarify the figures, 36V 10Ah is 360 watt-hours, equivalent to 360/12 = 30 amp-hours from your 12V battery. Two of those is 60Ah, and your 350W of solar should be capable of taking that in its stride, especially if you add a bit more battery storage.

The charger seems to run at over 70W, so if we say 100W, that's about 8A at 12V. Two of them, at 16A, is not a great strain on the battery, so charging anytime is OK. assuming you can refill the battery promptly. However with the present 85Ah leisure battery that's not enough to charge both batteries without solar or alternator contributing some charge too.

 

[Jamesh]

This is also presuming the OP is going to drain the battery fully on every ride. If they are just going into town occasionally they might only use 25%of power used and there for power used to recharge will be 25% too.

Cheers James

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