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Using vehicles 12v battery as the leisure battery for a camper conversion

9393 Views 21 Replies 8 Participants Last post by  Mike from NB, 
peteappleyard
Hi guys,

I posted this in the e-NV200 forum too, as that's the vehicle I have, but it's quite a general point so might be of interest to everyone...

So I'm just planning the electrics system for my e-NV200 camper conversion and had a thought...

In the past (in ICE campers) I've always used leisure batteries for the camper electrics, charged from the alternator via a battery-to-battery charge system (as well as solar and a 230v mains charger). But, in an electric vehicle, is there any reason I can't use the 12v under the bonnet?

Conventionally, the starter battery in an ICE vehicle will deliver a high surge current to start the engine, but won't like being deep discharged. Your leisure battery is the opposite and won't deliver a huge surge current, but will be more tolerant to bring deep discharged. So as far as I can see, the main reason for using a specific leisure battery as opposed as a starter battery, for your camper electrics (other than the obvious reason of not draining your starter battery whilst camping) is because the two batteries are actually different technologies (one for high surge low discharge, and the other for low surge but high discharge)

So it got me thinking... why can't I replace the 12v battery under the bonnet of my e-NV200 with a high capacity battery (maybe AGM or lithium) of 200Ah, and use that to provide 12v power to both the vehicle, and the camper 'leisure' electrics?

Our EVs don't pull a surge current from the battery when they start - they just use the 12v to keep systems running and boot up the vehicles drive systems etc. So if there's no surge current required, a 'leisure' type battery should be able to replace the factory 12v, no?

The benefits that I can see are:
*Only one 12v needed in the vehicle rather than 2, saving weight and space.
*No battery-to-battery charger or split charge relay required.
*No additional 230v mains charger required for the leisure battery, as the 12v charges when we plug the vehicle in (I assume?)
*There's plenty of space under the bonnet to fit the inverter and solar charge controller.

The only negative I can see is that you'd need to ensure that you don't drain the battery (rendering you unable to start the vehicle). Or does the vehicle sense when the 12v is low, and charge it via the DC-to-DC, automatically? Either way, you can fit a voltage sensitive relay, that cuts power to the 'leisure' system when the battery gets to a certain percentage state of charge, to ensure that there's always power available to start the vehicle.

Any thoughts on this? I'm sure many of you guys are far more clued up than me

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H
There are reports on the Leaf 24/30kWh forum of the Leaf electronics (and presumably the env200 electronics) being very sensitive to lower than expected 12v voltages.

I would go for split batteries as per ICE campervans, especially if you have a fridge, so that you can be sure of having sufficient 12v to get the vehicle electronics to power up correctly.
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peteappleyard
Hilltop Dave said:
There are reports on the Leaf 24/30kWh forum of the Leaf electronics (and presumably the env200 electronics) being very sensitive to lower than expected 12v voltages.

I would go for split batteries as per ICE campervans, especially if you have a fridge, so that you can be sure of having sufficient 12v to get the vehicle electronics to power up correctly.
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Ah yes, that makes sense. But I wonder does the eNV200 have any kind of auto switch-on of the DC to DC converter, so that it will keep the 12v topped up, even if the vehicle isn't 'started'?

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dk6780
No, it does not defend the 12V battery in that way. The early models were worse than the later ones, but they all require the car to be powered on to run the DC-DC charger for the 12V battery, and you cannot power the car on unless the 12V battery has a healthy charge. Running anything significant off of it for any length of time without the car powered on risks not being able to start, and the vehicle powers down after less than an hour unless being driven so leaving it on is not an option. The only sense is to fit a second battery with split charge as previously suggested. There is plenty of room to do so under the bonnet.
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peteappleyard
dk6780 said:
No, it does not defend the 12V battery in that way. The early models were worse than the later ones, but they all require the car to be powered on to run the DC-DC charger for the 12V battery, and you cannot power the car on unless the 12V battery has a healthy charge. Running anything significant off of it for any length of time without the car powered on risks not being able to start, and the vehicle powers down after less than an hour unless being driven so leaving it on is not an option. The only sense is to fit a second battery with split charge as previously suggested. There is plenty of room to do so under the bonnet.
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Thank you for clarifying. I guess the main objective was saving money (not needing to have the split charge relay and a separate mains 12v charger, but what you've said makes sense.

Many thanks

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H
peteappleyard said:
Thank you for clarifying. I guess the main objective was saving money (not needing to have the split charge relay and a separate mains 12v charger, but what you've said makes sense.
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Does the Leaf / env200 DC-DC converter operate while the vehicle traction battery is being charged? 12v will be required to operate the HV contactor and the BMS electronics (to control the traction battery charging current); would it be possible for a separate 12v leisure battery to be charged at this time from the main 12v battery via the split charge relay? [One problem may be that after a period, the DC-DC converter drops its 12v output from a charging voltage to a floating voltage].
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dk6780
Yes. The voltage only drops to a float once the battery is charged. The only question in my mind is whether you want to have to charge at a minimum of 6A mains AC to get the car to charge, or do you want the option of charging just the 12V? If you were say at a campsite the latter may be the most cost effective solution and an alternative to carrying the granny lead.
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donald
You can just leave the van on all the time, it will continually power the 12V circuit from the HV battery via the DC-DC converter.
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Jan Arne
donald said:
You can just leave the van on all the time, it will continually power the 12V circuit from the HV battery via the DC-DC converter.
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Im planning to do just that, but does anyone her know how many Watts the dc-dc converter can put out. I've read different things but only reffering to different models of the leaf. I have a 2014 env200 myself
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donald
For guidance, BEV DC-DC converters are usually in the 1 to 2kW range. Not sure of the Nissan specifics.
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Jan Arne
Hmm I need specifics ?
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Glyn Hudson
The e-NV200 has a 135 Amps (about 1.7KW) 12V DC-DC converter. I've had no problem pulling 800W from it and using it as a campervan leisure battery. I just keep the van switched on when I want to draw lots of power. I often leave the van on all the time the run the heating / A/C anyway.

Here's a video showing my inverter setup in my e-NV200 campervan:
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Jayne
I wonder if when EVs are designed specifically as campers if it'll be possible to power the electrics directly from the traction battery. If you're sitting on say 100kWh of high voltage battery it would make sense to be able to use that power for things like a fridge, cooker and heating to avoid having to cart around yet more (leisure) batteries and gas tanks. In fact avoiding gas full stop would be a huge plus in my view.

I just know the basic concepts of transformers and inverters, not their practicalities. I have no idea if it's feasible in a van sized setting. But I do remember seeing a Fully Charged video with them sitting round a picnic table with a standard kettle plugged into the front of the car, next to the charging sockets, making a cup of tea. Lightyear One maybe? And vague memories of something in the Rivian camper concept? So I'm hopeful it'll be possible.
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donald
Jayne said:
I wonder if when EVs are designed specifically as campers if it'll be possible to power the electrics directly from the traction battery. If you're sitting on say 100kWh of high voltage battery it would make sense to be able to use that power for things like a fridge, cooker and heating to avoid having to cart around yet more (leisure) batteries and gas tanks. In fact avoiding gas full stop would be a huge plus in my view.

I just know the basic concepts of transformers and inverters, not their practicalities. I have no idea if it's feasible in a van sized setting. But I do remember seeing a Fully Charged video with them sitting round a picnic table with a standard kettle plugged into the front of the car, next to the charging sockets, making a cup of tea. Lightyear One maybe? And vague memories of something in the Rivian camper concept? So I'm hopeful it'll be possible.
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It's already possible and you can do it today if you like.

The DC-DC converters on most EVs are around 1.5 to 2kW capable, so if you attach a, say, 800W inverter to your 12V battery and leave the EV 'on' then it'll basically be powering your inverter directly.

I would not propose to go over 800 ish Watts if you do that, you will be loading up the DC-DC converter more than it is designed to go.

I will also add that this is on your own decision, I have to recommend you 'don't' do this! But of course you can, whether that is enough power for you or not I can't say.

The other way to do it, and safer, is to use a separate leisure battery to your high power inverter running your electricals. When your leisure battery is going a bit flat, connect it with jump leads to your EVs battery and then start the EV up. You'll need at least 10V to start it, so obviously don't flatten your leisure battery too far. The EV will then see the combined battery as its 12V and charge them both up.

Having a spare battery and jump leads also means that if the 12V on the EV is the one that goes flat, you can jump start it!! ;)

Of course you were asking about heating and such, and unfortunately most EVs are not yet geared to provide external power in that level. You could, however, rig up some vent system from in the EV to your tent/caravan and leave the EV heaters (and AC) on and vent through to your torture-of-choice. ;)
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Jayne
I suppose my question was whether it's possible now (not quite), not yet possible or simply not possible.

Looks like a separate leisure battery is still a requirement.

Mind you, right now it's all a bit of a pipe dream anyway. I don't want to go back to diesel and van based EVs aren't quite at the range I'd be looking for, though they're not too far away now. Dread to think what price they'll be though.
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donald
Jayne said:
I suppose my question was whether it's possible now (not quite), not yet possible or simply not possible.

Looks like a separate leisure battery is still a requirement.

Mind you, right now it's all a bit of a pipe dream anyway. I don't want to go back to diesel and van based EVs aren't quite at the range I'd be looking for, though they're not too far away now. Dread to think what price they'll be though.
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I'd have said 'not quite possible' but you can take advantage of the battery and do most of what you want to do, if you do a bit of fiddling.
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Glyn Hudson
Jayne said:
Looks like a separate leisure battery is still a requirement.
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A leisure battery is definitely not a requirement. I've been on lots of long trips in my e-NV200 without any leisure battery, I don't see the need when the van has large battery already. I just keep the van switched and I had 1700W available from the DC-DC converter, although 700W to power an induction hob is all I need:

I understand the reason why some people may still want a leisure battery, but I was keen to save on space.
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donald
Glyn Hudson said:
A leisure battery is definitely not a requirement. I've been on lots of long trips in my e-NV200 without any leisure battery, I don't see the need when the van has large battery already. I just keep the van switched and I had 1700W available from the DC-DC converter, although 700W to power an induction hob is all I need:

I understand the reason why some people may still want a leisure battery, but I was keen to save on space.
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The issue is the risk of blowing up your converter, it is not rated for that sort of continuous use, but if you have gotten away with a 600W device then that sounds ideal.

The technical issue to my mind is going over 1kW, which obviously excludes electric heating options.
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Glyn Hudson
donald said:
The issue is the risk of blowing up your converter, it is not rated for that sort of continuous use, but if you have gotten away with a 600W device then that sounds ideal.

The technical issue to my mind is going over 1kW, which obviously excludes electric heating options.
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The DC-DC converter is rated a 135A approx 1700W. Drawing up to 1000W will be no problem. Besides the power is being drawn from the battery not the converter directly, if you do draw more than 135A the battery will supply the excess.

No need to use 12V for heating. The van has got a built in 4kW/5kW (depending on region) electric heater which runs off the high voltage 400V DC.
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donald
Glyn Hudson said:
The DC-DC converter is rated a 135A approx 1700W. Drawing up to 1000W will be no problem. Besides the power is being drawn from the battery not the converter directly, if you do draw more than 135A the battery will supply the excess.

No need to use 12V for heating. The van has got a built in 4kW/5kW (depending on region) electric heater which runs off the high voltage 400V DC.
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I completely agree, most are 1.5 to 2kW.

The concern I have is not so much the absolute power but sudden power transitions whilst loaded with a high load. That's why it's OK to put, say, a flat 12V battery loaded against the converter, the converter will ramp up in power to deliver the voltage gradually on power up so it can deliver 2kW but not so good with sudden transitions on and off. If there is a sudden transient in voltage demand it will not 'understand' that, it's designed to charge a battery.

It has to withstand a certain variation in drawn power, of course, and the battery will buffer this, but within tolerances. At max load it is obviously being pushed harder. It will take it ... occasionally .. but you are stressing it to its max rating.

I am perhaps being over-cautious, but I know what goes into HV switching converters like this to deliver to 'a' particular need, and it'll be designed for a purpose. If you have maxed out the power and suddenly power off, or vice versa, and end up with a damaged converter then don't say no-one told you this might happen!

Good luck! ;)
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