Electrical Experts - Help !

Sep 16, 2013
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Not as dramatic as the title suggests, but would love a few glances over this drawing to make sure I haven't missed a fuse or have the wrong size cable somewhere etc

This is the major 12v wiring going into my van, from start to fuse boards.

The system will be powered by a 400Ah Winston LiFeYPO4 battery with 123 Smart BMS. The only thing this changes from a normal Lead-Acid battery system is the chargers and the relay.

Initial-Wiring.jpg

I have almost everything here to install. Just need to order the charger and inverter (in hand) and a few odds and sods. It's the odds and sods I've done the drawing for, as was losing track of what I need to buy o_O

From the leisure battery positive there is a 150A master fuse.

From the fuse the cable splits into two. This is so all inputs (chargers) run over one cable and all outputs (12v devices, inverter) on the other. This allows my battery management system (BMS) to read input and output currents separately. It can then switch either off if needed, and gives real-time data on battery charge level, charge status and usage to my phone.

For anyone interested, the charger I've chosen works with the BMS to shut off charging if needed. The relay controls the outputs.

All wiring to the inverter needs to be 35mm. Wiring between the leisure and starter battery, and charger needs to be 25mm.

I'm using three separate fuse boards in my van, each with their own negative connections point. I've done it this way as there's a lot of electrics being fitted and having the three fuse boards in different sections of the van makes cabling simpler (no voltage drop annoyances).

I haven't bothered with an isolator as I can pop a fuse if needed.

Just noticed I forgot the fuses between the starter battery and charger. I'll add one either end of this cable (charger charges both batteries).

Can anyone spot anything I've missed? Or something that's wrong?

Really appreciate any help. Head is spinning today :D2
 

eddievanbitz

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Oct 4, 2007
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Your 200amp fuse may be too low for a 2000w inverter. You'll need to look at the spec and see what the surge rate it has. Many inverters will surge on start up much higher than the rated output. The spec will tell you what you need
 
Jan 19, 2014
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This allows my battery management system (BMS) to read input and output currents
I rember reading your first thread on your proposed set up..it sounds impressive..
Not quite sure what the need is to monitor two lines in this way... surely it is only necessary for the system to know the net result.... ie either a charging current or a discharge current , to establish the state of the battery bank... current can' flow both ways at the same time.. it' either going in ie charging or going out discharging... so there only needs to be a shunt in the main cable out to monitor that.. ... that would be the norm I think... I've most probably missed something:).
Andy.

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Lenny HB

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Looks fine to me, if anything the 25mm sq cables to the vehicle battery a bit OTT but it never hurts to have them too big. That Votronic unit you have chosen looks a nice bit of kit.
 
OP
Wissel
Sep 16, 2013
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I rember reading your first thread on your proposed set up..it sounds impressive..
Not quite sure what the need is to monitor two lines in this way... surely it is only necessary for the system to know the net result.... ie either a charging current or a discharge current , to establish the state of the battery bank... current can' flow both ways at the same time.. it' either going in ie charging or going out discharging... so there only needs to be a shunt in the main cable out to monitor that.. ... that would be the norm I think... I've most probably missed something:).
Andy.

You're kind of right Andy. To protect the battery the BMS really only needs to know temperature and voltage, then have the means to switch charges and loads on and off. This is all done without the current sensors.

What the current sensors do do (when fitted this way) is give accurate charge and load figures. I'll know exactly how many amps are going into the battery whilst driving, or from solar when parked etc. This is one area that LiFePO4 is very different to lead-acid. Don't even need a shunt :)

Looks fine to me, if anything the 25mm sq cables to the vehicle battery a bit OTT but it never hurts to have them too big. That Votronic unit you have chosen looks a nice bit of kit.

Cheers Lenny. Your right on the 25mm cable, but like you say, bigger won't do any harm (and I have loads of 25mm already so no cost).

Charger looks good doesn't it :)

Such a simple solution.

Any chance of a link to the battery supplier?

Thanks

Of course Robert. The cells and BMS can both be bought in Europe from these people:
https://www.ev-power.eu/Winston-40Ah-200Ah/?cur=1

It's worse than that Eddie, that's a 200A (switching ?) relay.....The main battery fuse is only 150A.

Yep Pappajohn. For that fuse I went off the specs of my current setup (also quite a big setup, but no inverter). Not ordered the Inverter yet, when I do and have the spec I'll pick the right fuse.

Thanks all. Kind of relieved the worst mistake so far seems to be a possible fuse size :)
 

pappajohn

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Why? the fuse should be lower than the max current of the relay contacts.
The inverter at full chat will pull 166amps plus any other 12v drain. The fuse needs to be bigger to take account of any startup surge.
Unless of course, it's a continuous 1000w inverter with a peak output of 2000w.

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OP
Wissel
Sep 16, 2013
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Just double checked and inverter I'm looking at is actually 1500w (PSW).

Tbh the inverter is only really to power the Missus's hairdryer (at the setting she uses was way under 1000w, can't remember exact but we have checked everything with watt metre) and my Tassimo (1300w rated and almost exactly this at the wall).

Most of our stuff is 12v or 5v.

Of course I'll still be checking the fuse rating once it's here.
 

Robert Clark

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The battery pack seems remarkably cheap at about €1000, compared with say Victron or Mastervolt

Is the quality any good at that price?
 
OP
Wissel
Sep 16, 2013
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The battery pack seems remarkably cheap at about €1000, compared with say Victron or Mastervolt

Is the quality any good at that price?

I did a huge amount of research and couldn't find anything bad written about them Robert. They have been around for a good few years and widely used in things like electric cars (lots about them on US forums) and used a lot in yachts. I read enough to convince myself they were a good choice anyway.

They don't have a BMS built in like the Victron's etc, but are definitely better value as long as they do what they say they do.

I'll do regular updates on how this system is working which I hope will help others before buying. As I assume your in no hurry hopefully these will help :)

EDIT - the prices on that site are plus VAT

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two

Aug 4, 2011
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10cm from Battery to MegaFuse may be a bit short. If your making the wires up yourself, check before you cut. Thick wires are not very flexible, especially near to their terminations. If there are angles to accommodate, you may need a greater length. Will the fuse really be that close (but it’s good to have such short cables if they fit)?

I’d fit an isolator. Popping a fuse is not easy if they are bolted in. So a little bit more (red) cable would be required.

Check the termination diameters. I reckon that many need only be 8mm rather than 10mm (if that’s what you mean by ‘lug’) and double-check the size for the battery – 14mm is big, but I’m not familiar with those.
 
OP
Wissel
Sep 16, 2013
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10cm from Battery to MegaFuse may be a bit short. If your making the wires up yourself, check before you cut. Thick wires are not very flexible, especially near to their terminations. If there are angles to accommodate, you may need a greater length. Will the fuse really be that close (but it’s good to have such short cables if they fit)?

I’d fit an isolator. Popping a fuse is not easy if they are bolted in. So a little bit more (red) cable would be required.

Check the termination diameters. I reckon that many need only be 8mm rather than 10mm (if that’s what you mean by ‘lug’) and double-check the size for the battery – 14mm is big, but I’m not familiar with those.

Thanks Rogher. I've just ordered the 35mm cable. It's marked as flexible but I'll have to wait until it's here to see how short I can go (will make the leads myself).

Think you might be right re the isolator. It's something I couldn't decide on, but I have a couple of 300A ones here so may as well.

You are right on the terminal sizes. Just checked and the megafuse is indeed 8mm (thanks).

The 14mm bolts on the battery are a pain in the a***. Such a strange size. I managed to get solder lugs to suit 35mm cable, but I needed smaller cable ones for part of the BMS. In the end I found 13mm ones I can drill out enough (these only carry 1a).

Thanks again.
 
Aug 6, 2013
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Depending on the relative positions of the inverter & fuseboards moving the negative busbar nearer to the fuseboards could mean a longer run of 35 sqmm but much shorter individual negatives. You also need a single decent bond to chassis for the leisure battery and another (separate) bond for the incoming mains supply earth.

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Minxy Girl

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Just make sure you keep good notes on what you've done ...

250_Circuit_Mod-1322811146.png
 
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To protect the battery the BMS really only needs to know temperature and voltage, then have the means to switch charges and loads on and off. This is all done without the current sensors.
I think that's not very clear. LiFePO4 batteries need current sensors even more than lead-acid types. The 123BMS has two current sensors, one for input, one for output. That's one more than most lead-acid systems. You're right that it doesn't use shunts to sense the current, but it uses current clamps instead.

I like the way it measures the temperature and voltage of each individual cell, and balances the voltages as necessary.

The one thing I don't like is the exposed circuit boards attached to the batteries. That's OK in a house solar installation, and would still be OK in a MH locker, I guess. I don't know how it would stand up to long-term vehicle vibration.

You do realise, I hope, that the two small relays on the 123BMS will not actually turn off the charging and discharging currents themselves? They need to be switching a proper heavy-duty relay, like your 200A beast on the load circuit - but there's no similar big relay on the charger side in your diagram.
 
OP
Wissel
Sep 16, 2013
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I think that's not very clear. LiFePO4 batteries need current sensors even more than lead-acid types. The 123BMS has two current sensors, one for input, one for output. That's one more than most lead-acid systems. You're right that it doesn't use shunts to sense the current, but it uses current clamps instead.

I like the way it measures the temperature and voltage of each individual cell, and balances the voltages as necessary.

The one thing I don't like is the exposed circuit boards attached to the batteries. That's OK in a house solar installation, and would still be OK in a MH locker, I guess. I don't know how it would stand up to long-term vehicle vibration.

You do realise, I hope, that the two small relays on the 123BMS will not actually turn off the charging and discharging currents themselves? They need to be switching a proper heavy-duty relay, like your 200A beast on the load circuit - but there's no similar big relay on the charger side in your diagram.

Thanks autorouter.

Regarding the current sensors, your right that the 123 has two and in how they operate. But it doesn't need both. For instance, if using something like a Victron inverter/charger, 123 say only the OUT sensor should be fitted.

Of course with current running in both directions on the same cable, through one sensor, the BMS can't see a different input and output current. Just a combined current. This was the point I was trying to make (badly it seems) :D

I kind of like the individual boards tbh. I like it keeps everything together and doesn't need multiple wires to a separate BMS unit. Mine will be built into a housing. I hope road vibration isn't an issue over time, I've not heard of any cases of this and the same system (except extended) is used in electric vehicles. Fingers crossed.

Just in case you're interested, 123 are releasing another system in a few months, that is a separate unit. They describe this unit as far more plug-and-play, but I don't have any other details on it.

Thanks for mentioning the relays. Again you are completely right. The 200A relay in my setup is connected to one of the smaller relays on the BMS to control the output side.

On the input side, a bigger relay isn't needed on certain chargers like some Victron units that have an external control port. The port is connected directly to the small BMS relay. The Votronic charger in my drawing has this port.

Thanks again :)

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OP
Wissel
Sep 16, 2013
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I've made a few changes:

1. I've added isolators for starter battery, leisure battery and inverter.
2. I've added fuses either end of the cable between starter battery and charger
3. I've added a fuse from positive busbar to inverter

Here's the new drawing:

Initial-WiringV2.jpg


As before, I'd really appreciate any comments on this.
Thanks, David
 
Jan 19, 2014
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Of course with current running in both directions on the same cable
I'm confused again ..that can' happen I don' think... current will flow in one direction only at any one time in any given cable... that' what I was saying in my original reply.. and wondering why the need for two sensors for the system to monitor battery state...
If there was a current sensor on the main battery cable it would check whether the net result was a charging current or the batteries were having to supply any shortfall to the energy needs at any particular time...And that way the net battery capacity is monitored..
I understand what is been said about the type of sensor been a clamp type as opposed to a shunt....
Andy.

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two

Aug 4, 2011
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I've made a few changes:

1. I've added isolators for starter battery, leisure battery and inverter.
2. I've added fuses either end of the cable between starter battery and charger
3. I've added a fuse from positive busbar to inverter

As before, I'd really appreciate any comments on this.
Thanks, David


I'd put the mega fuse before your battery isolator
 
OP
Wissel
Sep 16, 2013
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I'm confused again ..that can' happen I don' think... current will flow in one direction only at any one time in any given cable... that' what I was saying in my original reply.. and wondering why the need for two sensors for the system to monitor battery state...
If there was a current sensor on the main battery cable it would check whether the net result was a charging current or the batteries were having to supply any shortfall to the energy needs at any particular time...And that way the net battery capacity is monitored..
I understand what is been said about the type of sensor been a clamp type as opposed to a shunt....
Andy.

I think it's me not explaining myself well Andy :)

With one current sensor seeing the charge current, and another showing the load current, the BMS app can show both figures independently. It then shows the battery state as a third figure.

Here's an image of the BMS app working:
123 app.jpg
 
OP
Wissel
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I'd put the mega fuse before your battery isolator

I agree Rogher. My thinking when drawing was there are two wires after the fuse, so I'd need to add an extra isolator.

Brain fart moment I think, as I can go fuse - isolator - two cables from isolator.

Thanks, I'll change that over.

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Jan 19, 2014
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whats the advantage of using cable earth returns rather than chassis?

I did the same on my self build mind..
Think it makes for a more reliable system... easier to fault find and I had it in my head that with the opportunity for all sorts of electrical interferance possibilities on a modern vehicle it might help prevent that occurrng...
I used very few chassis returns and the few I did use are easily accessible..
Andy
 
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Wissel
Sep 16, 2013
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whats the advantage of using cable earth returns rather than chassis?

In my case it's to make any faults easy to trace.
I'll have three easily accessible earth points, one with each of the fuse boards.

I've had enough earthing problems with the crappy base vehicle electrics. Don't want some in the back as well :D2
 
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