INVERTER

Aug 14, 2020
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Hi Im New to the forum. I have a VWT6 camper. SWB - Highline - 3 tonne - 150 - Auto and Im really pleased with it. I want to recharge my bike and the range extender from the 12v supply. The bike manufacturer recommends a 300w inverter. Which one ? Any advice would be welcome.
 

Lenny HB

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Oct 18, 2007
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I would get at least a 500 watt as the switch mode power supplies that bike chargers use can draw a high start up current especially if they have not been used for a while.
Also get a Pure sine wave one, and it depends on how much you want to spend, if just for the boke a cheapish eBay one will be OK but if you want a decent one go for something like a Victron.
 

Kannon Fodda

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Definitely need Pure Sine Wave to work with the electronics of the bike's lithium charger. Major brands are often better as you need the internal electronics to be heavyweight.

The charger should have power ratings on it which will tell you the current draw and / or wattage. Online calculators will let you work out what that means in power output for the inverter. Add a little bit more for inefficiency of the inversion processes, both from your 12V vehicle up to the 230V out from the inverter and then back down to the bike charge. When allowed out again I'll be experimenting with a 375W Victron inverter for my Bosch 500 batteries with the compact charger.

But also think about the power capacity of your camper's battery. Recharging an e-bike battery takes time and will put a drain on your systems. If you are recharging whilst static, will you have enough left for your habitation use? Many recharge whilst driving along, but that may limit how much is going back into your leisure battery at the same time, and you'll need to be driving around for a good couple of hours or more if your bike battery was flat.

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OP
RossRoss
Aug 14, 2020
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OK. Here goes -
The van has a Victron AGM leisure battery - 110Ah. (75% discharge)
The Bike has a 250Wh battery & the range extender is also 250W.
 

pappajohn

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The Bike has a 250Wh battery & the range extender is also 250W.
The inverter is going to draw 40amps from your battery giving you around 2 hours before your battery is flat.... Your going to need at least one more battery if not two new ones.
IGNORE that.... That's the battery wattage not the charger input watts.
 
Jul 6, 2009
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You will use app 26 amps @ 12 volt d.c. to produce 1 amp @ 240 a.c. This allows for inverter inefficiency and cable losses. Care should be taken not to allow the batteries state of charge to fall below 50% or you will drastically shorten its life. AGM are not best suited to high current drains.

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Apr 27, 2016
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250Wh is the energy stored in the bike battery. That is equivalent to 250/12 = 21Ah from a 12V leisure battery. Allowing for inefficiencies in the inverter and the charging process, I'd guess more like 24Ah is required from the leisure battery to refill the bike battery from a very flat state. And about the same for the range extender.

The inverter power required will depend on how fast the bike battery is recharged - about 2 or 3 hours is usual. Also whether you want to recharge the battery and extender at he same time, or one at a time.

If it takes 2 hours, the power required is 250/2 = 125Wh per hour, ie 125 watts, for just the bike battery. There will probably be a very short startup surge as you first connect up the battery, up to 200 to 250W. Double that if charging the extender at the same time. So I reckon a 300W inverter would be fine. A good 300W inverter will be OK with a short startup surge of 600W.
 
OP
RossRoss
Aug 14, 2020
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Thanks for all the advice. It seems that the bike manufacturers recommendation is good and maybe Victron is a best to buy. Reckon I’ll put the question direct to Victron and see what they have to say !
 
Jan 22, 2013
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We charge 2×500wh Bosch ebike batteries using 1x 2Ah and 1x 4ah charger simultaneously.
200Ah lifepo4 hab batteries, 300W Sterling pure sine wave inverter. Inverter never moves above 275Watts and stays reasonably cool. Starts at 20A draw from batteries. System works well with 45A b2b and 270W solar.
Jon

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Nov 22, 2020
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It’s frustrating when people post off topic. And yet here I am. Whichever inverter, I would see if you can get one with a remote switch. Mine is under the seat and it’s a pain to get to the on off switch. I wish it was next to the plugs!
 
Jul 5, 2013
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It’s frustrating when people post off topic. And yet here I am. Whichever inverter, I would see if you can get one with a remote switch. Mine is under the seat and it’s a pain to get to the on off switch. I wish it was next to the plugs!
Same as mine except I had to go outside to access the switch. I cured it by fitting a heavy duty on/off switch to the 12v supply side of the inverter.
 
Apr 27, 2016
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It’s frustrating when people post off topic. And yet here I am. Whichever inverter, I would see if you can get one with a remote switch. Mine is under the seat and it’s a pain to get to the on off switch. I wish it was next to the plugs
I don't agree that it's off-topic. Many people, especially motorhome newbies, don't know that some inverters can have a remote switch, and some can't. They find out too late after they have bought one. They probably also don't know about switching off the inverter when not in use, to prevent unnecessary battery drain. Passing on that information is a key function of this forum.

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Dec 2, 2019
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RossRoss, what’s on the bike charger label? The power of that charger dictates the size of inverter, simples. If your charger is 150w, then a 200w inverter will be fine. Is all down to the bike charger appetite. Once you know how much it gobbles, you provide the appropriate spoon (inverter).
 
OP
RossRoss
Aug 14, 2020
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Heres the charger info - how do you translate the power from that ?

D1CAFCA8-C4EB-469E-A10A-1F7A0CD18E5D_1_201_a.jpeg
 
Dec 2, 2019
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Output of the charger is 42v x2a =84w
Input 100-240v @2a, max 480w
A 500w inverter will cover the input of that charger.

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Oct 29, 2008
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We have a 1000w Ring Pure sinewave inverter fitted on the rear of the passenger seat frame. We have 2 x 97ah AGM leisure batteries a 140w solar panel into a Votronic MPPT Duo regulator. We use it to charge our bikes and laptops and in summer when its sunny we use it for a toaster and travel electric kettle.
In retrospect, I should have gone for a 1500w inverter so I can run a nespresso machine.
 
Apr 27, 2016
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Output of the charger is 42v x2a =84w
That will charge a 250Wh battery in 250/84 = 3 hours. Plus about 10% for inefficiencies. The 4A charger will do the same in half the time.
Input 100-240v @2a, max 480w
As above, the steady-state power consumption is 84W. This 480W figure is the start-up surge, and is over very quickly. If you look at the inverter specification, the 'headline' power is the steady-state power, and the surge power is in the small print somewhere. It is often double the steady-state power.

Another point worth noting is, the input amps figure of 2A will be for the minimum input voltage of 100V. At 240V the amps will be less than half of that. So the surge power is probably only 100 x 2 = 200 watts, not 480 watts.

The downside of inverters is the wasted power just keeping the inverter running. A 90% efficient 1000W inverter will waste 100W at full output. But that figure is not proportional to the power output - in other words, if it's only outputting 100W, the wasted power will be much more than 10W, and probably nearer the 100W figure. For short bursts of power, like a coffee machine or a hair-dryer, it's not so important, but for longer low-power usage, it all adds up.

The upshot is, if you use an inverter for long periods - bike battery charging, fridge or phone charging - best to get one that's the minimum required for the job
 
Last edited:
OP
RossRoss
Aug 14, 2020
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So I wrote to Victron, as it’s their AGM battery i have installed in the van
I sent them all the info on bike and charger, and this is the response :

The charger uses 2amps (MAX), so if we size the inverter to this, you would need an inverter that can give a least 460watts (2amps x 230v = 460watts)
The issue is that if the ebike takes 2 hours to charge, then the 110Ah AGM battery, even if it is fully charged, may struggle to support the load for two hours.
From an inverter perspective, the following unit should suffice (it a little on the higher side), based on running one charger only, however, you may need to increase the battery capacity feeding it.

The inverter they suggest is a Victron 800 at a cost of £270

what do you think ?

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Apr 27, 2016
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The inverter they suggest is a Victron 800 at a cost of £270
Victron inverters are 250, 375, 500 and 800. jonasw19 in post #12 says one bike charger like yours, plus one twice the power, runs perfectly well on a 300W inverter. I'm sure your single bike charger will run on the 500 and 375 models, and probably the 250 model.

Chargers like these are generally quite efficient, more than 90%, much the same as inverters. If this charger takes 460W input and gives 84W output, that means its efficiency is 100 x 84 / 460 = 18%. I just don't believe that.

A pessimistic view would be that its efficiency is 80%, and since its output is 84 watts, its input will be no more than 84 x 100 / 80 = 105 watts.

The startup surge power is usually twice the steady-state power, about 210 watts, which is consistent with what I said in post#23.

Of course you may have other reasons to go for a higher power inverter, but better to decide knowing the facts rather than leap in the dark.
 
Dec 2, 2019
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I have a few dewalt 18v chargers, output says 4a 22v 195va. Gues how much W it eats?
One clue , a cheap sq 150w it trips on overload.

I agree the OP could do with the victron 250va very well with that charger.

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OP
RossRoss
Aug 14, 2020
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Thanks for all the advice and help guys.
I think ill go for a 375 or 500 with pure sine wave and a remote or bluetooth control.
 
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