Some electrics advice please.

Geek · Thursday at 10:50 AM

merl said:
Finally your old battery capacity monitor/display (assuming you've got one somewhere) will be next to useless with LFP and not accurate at all so consider adding a shunt style capacity monitor.

Agreed that voltage is no indicator, but a shunt style monitor is not great either.
The lower internal resistance of a lithium battery makes the shunt impedance more of an issue.
I use hall effect sensors instead. They're far from perfect, but they dont add impedance.

merl · Thursday at 11:20 AM

Geek said:
Agreed that voltage is no indicator, but a shunt style monitor is not great either.
The lower internal resistance of a lithium battery makes the shunt impedance more of an issue.
I use hall effect sensors instead. They're far from perfect, but they dont add impedance.

I've had a couple of monitors that use a shunt in the negative battery lead and they've been pretty decent WRT remaining capacity, not perfect and Yep the resistance of the shunt does drop a little voltage but it's not a lot especially on the higher current devices. I have the 250A Ai Li shunt at the moment and from memory it drops about the same voltage as 25cm of 70mm cable so not a lot. I have no experience of the hall effect sensors but have avoided them previously because I'd expect them to be insensitive/inaccurate at low currents? What's yours like at tens of milliamps?
I don't get your comments re the lower internal resistance of LFP (rather than LA) making a shunt resistance more significant? Maybe you could expand?

Geek · Thursday at 12:17 PM

I'm not sure how accurate the hall effect sensors are. They seem to work as an indication, but I've not got round to checking them for accuracy.

The lower resistance of the battery just makes the resistance if the shunt proportionately more significant.

I'm not sure where you get your 25cm of 70mm cable figure from.
I only use 25mm and 50mm. I find that 70 is too stiff to work with.

25mm copper is about 0.8 milliohm per metre, so a typical shunt (1.5milliohms) is equivalent to two metres of 25mm, four metres of 50mm or almost four metres of 70mm, not 25cm.

motoroamer · Thursday at 1:50 PM

Thanks very much merl and Geek. Gosh all that above is high tech. I still have a NASA monitor that uses a ground shunt but I don't really trust it so have just used my trusty old Fluke meter from my old life with Machine Tools for volts !

Anyway I'm getting quite apprehensive after all about removing the second Ford Battery in the Transit and getting into their SCR. It seems describing the second battery as an 'auxilliary' is missguiding.

Reading on the Transit Forum the second battery is really the Main Battery, the whole Body Battery, and the other is simply the starter motor battery. They are joined in parallel when the ignition is on and then they are both used for starting too ! The first is the starter battery and the second does everything else !

On the Transit Forum someone said;

"
Altransit wrote:
Unless you have changed the standard wiring, BOTH batteries are used for starting, and are also charged in parallel. They are only disconnected from each other when the ignition is switched off.

I'm no expert, but from what I've read on the subject, Lithium batteries are not suitable as substitutions for the standard batteries, and are unsuitable for charging from the standard charging setup.
Because of their use in a parallel circuit, they should both be similar in type, size and capacity."

I understand what you said Geek and how would the Transit know ? but I'm still a bit worried now about removing battery 2 and putting in the Lithium and the B to B into the Ford SCR. I sure wouldn't like to take out the Ford SCR just with my limited understanding of the drawings I obtained. Of course I can't find anyone at Ford that can help and I realise how difficult it is for you kind folk to advise.

I wonder if I just bought a B to B, disconnected the third battery and connected the B to B input to the + post of battery one (as you mentioned merl), and the output to the + post of the battery three now sitting alone. Then just discharging that battery and start up and seeing what happens. Maybe all three would be charging as it does now and the Ford factory won't get upset and everything will work OK. ? Then I could replace the third battery with a Lithium if my choice if it worked.

I know it's a bit inconvenient as you say Geek, having everything under the seats and very cramped but getting cable routes outside the seat positions is awful and I'm not keen on routing down underneath the floor outside then the back up inside to another venue. I reckon to get all I need inside both of the seats bases even if I may need to mount the B to B and solar control on the outside of the seat base box/es. I see the Victron stuff needs to be upright, I guess to let the heatsinks work.

There again I'm back to thinking about what you said Geek......."not removing the SCR is what leads to a disaster"

Maybe I should forget it and leave you all in peace.

Geek · Thursday at 4:25 PM

Basically, what I suggest is that you leave the first two batteries as-is, separate the habitation circuits and connect them to a new, large lithium battery. Charge that battery via a B2B charger. That way you can leave the SCR as it is.

Resiting the new battery if you want to should be (electrically) straightforward: you just need to connect it to the existing Autosleepers panel and heater fuse through a single 25mm cable.

Use a separate 25mm cable for the B2B connection.

motoroamer · Thursday at 4:37 PM

That sounds great so output of B to B to a new Lithium battery but where should I connect the input of B to B to ?

Geek · Thursday at 5:51 PM

To the starter battery. The B2B will come with instructions.

motoroamer · Thursday at 6:34 PM

Geek said:
To the starter battery. The B2B will come with instructions.

Thanks very much indeed Geek. As soon as it's warmer I'm going for it and I'll let you know how it's doing.

I've downloaded the Victron Orion XS instructions and am on page 10 so far. Good gracious when I order the B2B and a battery I'm going to have make sure the seller gives me all the details to set it up and help with info if necessary when I do it. I have to keep looking up what all the abbreviations means.

I'll need a collection of new cable and fittings as well gosh the cable is expensive. When I think of all the great cables we threw out when I worked in industry !

Peter D

Geek · Thursday at 6:39 PM

When you buy the cable, be sure to measure carefully to limit waste and get the super flexible sort (more, thinner strands) preferably with silicone insulation, not PVC. Slightly more expensive, but more docile. Often sold as welding table, I think.

merl · Thursday at 7:26 PM

Geek said:
so a typical shunt (1.5milliohms) is equivalent to two metres of 25mm

I don't think there's such a thing as a "typical shunt". I've fitted a few shunts for myself and others and no 2 have been the same. I fitted an AiLi 50A unit once and my installation meant that the batteries were about 1.8m away from the rest of the kit. In order to save the volts drop of the Shunt I used the resistance in part of the 1.8m connecting cable and connected the two shunt sense wires with 2 wires soldered to 2 thin sharp 'needles' which could be pushed through the insulation at any point along the 35mm supply cable, calibrated against my clamp meter I could move the probes up and down the cable until it was perfectly calibrated, they ended up around 1.1m apart.
I later added an inverter, and the 50A unit couldn't display the higher current when using high powered items so I swapped the AiLi display to a 250A unit. I assumed the new display would use the same shunt resistance as the original 50A unit but I'd doubled up the 35mm cable to handle the current and assumed the probe distance would therefore need to be doubled to 2.2m. WRONG! The displays obviously dont all ise the same shunt value and the new 250A shunt was WAY lower in resistance and only needed (from memory) to be around 10" apart. I could be slightly out but it certainly wasn't four metres! It's persisting it down out there at the moment, tomorrow I'll pop down to the van and take some readings.

Geek · Thursday at 7:44 PM

merl said:
I don't think there's such a thing as a "typical shunt". I've fitted a few shunts for myself and others and no 2 have been the same. I fitted an AiLi 50A unit once and my installation meant that the batteries were about 1.8m away from the rest of the kit. In order to save the volts drop of the Shunt I used the resistance in part of the 1.8m connecting cable and connected the two shunt sense wires with 2 wires soldered to 2 thin sharp 'needles' which could be pushed through the insulation at any point along the 35mm supply cable, calibrated against my clamp meter I could move the probes up and down the cable until it was perfectly calibrated, they ended up around 1.1m apart.
I later added an inverter, and the 50A unit couldn't display the higher current when using high powered items so I swapped the AiLi display to a 250A unit. I assumed the new display would use the same shunt resistance as the original 50A unit but I'd doubled up the 35mm cable to handle the current and assumed the probe distance would therefore need to be doubled to 2.2m. WRONG! The displays obviously dont all ise the same shunt value and the new 250A shunt was WAY lower in resistance and only needed (from memory) to be around 10" apart. I could be slightly out but it certainly wasn't four metres! It's persisting it down out there at the moment, tomorrow I'll pop down to the van and take some readings.

I have three or four shunt meters of different makes. Most run at 50mV or 75mV at max rated current.

The impedance per KM is often written on good quality cable. It is in several of mine. Of course, ohms per km is also milliohms per metre.

motoroamer · Thursday at 8:44 PM

Geek said:
When you buy the cable, be sure to measure carefully to limit waste and get the super flexible sort (more, thinner strands) preferably with silicone insulation, not PVC. Slightly more expensive, but more docile. Often sold as welding table, I think.

I will do so and if I need a bit more battery cable I will use welding cable, I did that before. I liked the multi strand we used for switchgear panel wiring we used in industry, it was actually called Panel Wire I believe lots of strands, we always used bootlace ferrules. I have never considered the insulation before but the more docile the better. I'll guess meter leads will be silicone then as they have a nice feel.

Thanks again

Some electrics advice please.

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