Van wiring

[Master2021]

Hey everyone I have a 2021 renault master van and I'm looking to put a 2nd battery in the rear to run an inverter for charging power tool batteries.
Im jus wondering whats stopping me from just fusing the cable and putting a manual isolation switch on it instead of using relays.
Thanks

 

[68c]

I suppose you mean thinnish cable between the starter and leisure batteries to only carry the charging load with a switch and inline fuse. So should you forget to turn off the switch and start the engine the fuse will blow to protect the wire.
Yes, this works and is a common solution on work vans rather than motorhomes.

 

[pappajohn]

Or put the inverter on the starter battery and charge tools etc while driving.

 

[Raul]

Hey everyone I have a 2021 renault master van and I'm looking to put a 2nd battery in the rear to run an inverter for charging power tool batteries.
Im jus wondering whats stopping me from just fusing the cable and putting a manual isolation switch on it instead of using relays.
Thanks

What sort of batteries do you charge? I use a dewalt 18v automotive charger direct on the 12v socket without inverter. It charges a 5ah dewalt 18v battery in about 1hr 20-30mins from flat. The 4ah ones in just over a hr. I’m sure you can get automotive chargers to avoid the inverter for this type of use. Much more efficient to.

 

[Master2021]

I'm charging various different tools I also wanted to use the inverter for a microwave

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[Master2021]

Or put the inverter on the starter battery and charge tools etc while driving.

But is there any harm in doing it the way I said

 

[pappajohn]

But is there any harm in doing it the way I said

None, unless you forget to switch on the isolator then you you need to replace the fuse.
OK if it's easily accessible otherwise a pain in the neck.

 

[cmcardle75]

But is there any harm in doing it the way I said

No harm in it, but the charging will be pretty ineffective as the 2021 Master will have a smart alternator that will rarely provide enough voltage to charge the auxilliary battery. Smart alternators will typically require a B2B charger, or be mounted almost directly to the vehicle battery with a very low resistance path and the same battery chemistry.

 

[Lenny HB]

If you want to run a microwave you are going to need 2 or 3 batteries as if you use a single 100a/h battery it won't last long. A 800 watt microwave will draw arout 70 amps running from an inverter and probably twice that on start up.
To get a decent charge rate to charge the batteries you will need to fit a B2B (battery to battery charger).

 

[Master2021]

If you want to run a microwave you are going to need 2 or 3 batteries as if you use a single 100a/h battery it won't last long. A 800 watt microwave will draw arout 70 amps running from an inverter and probably twice that on start up.
To get a decent charge rate to charge the batteries you will need to fit a B2B (battery to battery charger).

Perfect and could you recommend a b2b charger

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[Lenny HB]

Perfect and could you recommend a b2b charger

The 3 main ones people use are Sterling, Victron & Votronic. Both Victron & Votronic are very good, I've had problems with a Sterling and I don't think they are as well made.

 

[cmcardle75]

If you want to run a microwave you are going to need 2 or 3 batteries as if you use a single 100a/h battery it won't last long. A 800 watt microwave will draw arout 70 amps running from an inverter and probably twice that on start up.
To get a decent charge rate to charge the batteries you will need to fit a B2B (battery to battery charger).

The total amount taken should be OK, if it's only on for 5 minutes. It'll actually be more than 70A, as the microwave is rated as output power and is nowhere near 100% efficient. Also, lead acid chemistry is much less efficient at higher rates, whilst Lithium is pretty constant. Even so, there'd be enough to do a few microwave meals between charges. However, driving around town to actually charge it isn't a goer without a 60A B2B to actually charge the thing, or plugging in overnight. It would be much better with LiFePO4, but that is clearly an investment too far, I'd think (although in this application a 50Ah LiFePO4 would be more effective than a 200A lead acid due to lithium's increased power efficiency and discharge ability, so it might actually be worth it).

 

[cmcardle75]

The total amount taken should be OK, if it's only on for 5 minutes. It'll actually be more than 70A, as the microwave is rated as output power and is nowhere near 100% efficient. Also, lead acid chemistry is much less efficient at higher rates, whilst Lithium is pretty constant. Even so, there'd be enough to do a few microwave meals between charges. However, driving around town to actually charge it isn't a goer without a 60A B2B to actually charge the thing, or plugging in overnight. It would be much better with LiFePO4, but that is clearly an investment too far, I'd think (although in this application a 50Ah LiFePO4 would be more effective than a 200A lead acid due to lithium's increased power efficiency and discharge ability, so it might actually be worth it).

I can't help thinking, though, that the outlay on equipment to reliably microwave for 10 minutes every day would be better spent on a little gas stove. A few standard power tools (i.e. the sort of 5Ah batteries used on drills/saws etc.) could be taken off the main vehicle battery and you could save yourself a packet.

 

[Raul]

I'm charging various different tools I also wanted to use the inverter for a microwave

I have a 2kva inverter for various things in the van like kettle, mini oven, induction plate, toaster etc. However, when I charge the tools batteries, I use the automotive charger. Only if the inverter is on for other thinks I would use a wall charger as well. But this is of 400ah lithium. Running a microwave via inverter of a starter battery is bonkers. A starter is a SLI classification battery: starting lights ignition. For a inverter is necessary a heavy duty deep cycle battery to cope with the discharge rate and sustained draw. And a max 20% discharge rate. That’s 20a out of a 100 amper bat.
If you don’t believe me do a test, you can’t beat the lows of physics, especially the law of energy conservation. You will be hit by mister peukert with a heavy voltage drop until inverter shuts down before you done. Batteries do not store power, it’s a chemical reaction that creates it. That chemical reaction has limitations, in many ways. So if you want to run a 1000w via inverter, you will need to supply that inverter with approx 90a from 500ah lead, or 300ah lithium. You could go 200ah lithium with occasional use of 50% draw, but for better life 30% is recommended rate. Of course this is just a example, you can adjust the numbers to your needs.

 

[cmcardle75]

I have a 2kva inverter for various things in the van like kettle, mini oven, induction plate, toaster etc. However, when I charge the tools batteries, I use the automotive charger. Only if the inverter is on for other thinks I would use a wall charger as well. But this is of 400ah lithium. Running a microwave via inverter of a starter battery is bonkers. A starter is a SLI classification battery: starting lights ignition. For a inverter is necessary a heavy duty deep cycle battery to cope with the discharge rate and sustained draw. And a max 20% discharge rate. That’s 20a out of a 100 amper bat.
If you don’t believe me do a test, you can’t beat the lows of physics, especially the law of energy conservation. You will be hit by mister peukert with a heavy voltage drop until inverter shuts down before you done. Batteries do not store power, it’s a chemical reaction that creates it. That chemical reaction has limitations, in many ways. So if you want to run a 1000w via inverter, you will need to supply that inverter with approx 90a from 500ah lead, or 300ah lithium. You could go 200ah lithium with occasional use of 50% draw, but for better life 30% is recommended rate. Of course this is just a example, you can adjust the numbers to your needs.

I'd say Lithium is pretty good even up to 1C discharge rate, let alone 0.5C. However, lead acid, as you say, becomes very inefficient at much lower rates. Obviously, it can do higher rates, but it results in wear if done for any period, and is electrically inefficient.

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[Raul]

For how long? Look on the big cell manufacturers white papers and see what they say, don’t be confused by the publicity quotes of max draw or up to. They all quote the max figures, but fail to mention the associated conditions for that max. Remember, good publicity sells. Lifepo4 can actually reach 3C for 5mins, ( winston cells), but you will pay for it. A max 0,2C charge and 0,3C discharge should outlast your van, or in excess of 5000 cycles. The fact it says max 1C on the striker, does not mean you can go there without penalty.

 

[cmcardle75]

For how long? Look on the big cell manufacturers white papers and see what they say, don’t be confused by the publicity quotes of max draw or up to. They all quote the max figures, but fail to mention the associated conditions for that max. Remember, good publicity sells. Lifepo4 can actually reach 3C for 5mins, ( winston cells), but you will pay for it. A max 0,2C charge and 0,3C discharge should outlast your van, or in excess of 5000 cycles. The fact it says max 1C on the striker, does not mean you can go there without penalty.

Not without penalty, but, for many people's occasionaly usage patterns, 1C discharge for non-trivial periods (i.e. the few seconds to start an engine) is still going to last many, many years. LiFePo4 really can cope with 1C charge and 1C discharge. Yes, you'll get longer life limiting yourself to 0.2C. However, this just extends the life long past you've sold or scrapped the unit it was installed into. With similar usage on a lead acid, you'd be lucky to survive the weekend without burns.

 

[pappajohn]

S'funny..... Folks never had a real issue with inverters and lead acid batteries... They just got on with it.... then along came Lithium and lead acid is now the weak link and bad boy. .

 

[Raul]

S'funny..... Folks never had a real issue with inverters and lead acid batteries... They just got on with it.... then along came Lithium and lead acid is now the weak link and bad boy. .

My hole house runs on lead batteries, as long as it’s within parameters and know the limitation, careful usage without much abuse, will give you good service. This March the existing battery bank comes to 5 years of service, and I hope to get a couple more at least.