DIY Lithium

Trotter

Full Member
Posts
706
Likes
877
2001 Ducato alternator will have a decent rated current output - enough for what you want.
All you can really check yourself is the voltage which again should be high enough.
One advantage of old style alternators is that they don't have any fancy controls stopping them 'working'
I read somewhere that narrowboats often have a second alternator fitted. For the leisure side?
I don’t suppose for a minute that this would be an option in a Fiat. So, taking a charge after the vehicle battery makes sense to me. Satisfy the vehicle, then the leisure side.
 

Derekoak

Full Member
Posts
475
Likes
322
I cant find any data on the alternator of my 2017, doblo xl, 1.6litre. Not online or in my fiat handbook. The nearest I can find is that suggested replacement alternators have 100, 120 or 150 amp output. What the existing one is I do not know, let alone the charge voltage. I have a multimeter. I assume I must disconnect the alternator to get an open circuit voltage?
I already have an unused 6mm wire running from the starter battery to a suspect split charge and power relay alongside the 30 amp ring b2b I use. I hoped to charge a depleted battery faster than 30 amp initially, but never really needed it.
Its about 2m from sb to lb. There must be lost volts on that journey?
 

Markd

Full Member
Posts
719
Likes
408
Anything is possible if you want!

Narrow boat alternators are slightly specialist installations.
Because the engine generally revs quite slowly the 'gearing' of the alternator needs to take this into account to get it up to a decent speed to deliver highish current without overheating.

You could put in a higher output alternator but need to check whether it delivers that power at normal engine revs.

Steling power have a good videos on these points.
 

wildebus

Full Member
Posts
4,035
Likes
4,265
I cant find any data on the alternator of my 2017, doblo xl, 1.6litre. Not online or in my fiat handbook. The nearest I can find is that suggested replacement alternators have 100, 120 or 150 amp output. What the existing one is I do not know, let alone the charge voltage. I have a multimeter. I assume I must disconnect the alternator to get an open circuit voltage?
I already have an unused 6mm wire running from the starter battery to a suspect split charge and power relay alongside the 30 amp ring b2b I use. I hoped to charge a depleted battery faster than 30 amp initially, but never really needed it.
Its about 2m from sb to lb. There must be lost volts on that journey?
If you have, or can borrow, a Multimeter with a Clamp for current (like this one for example - https://amzn.to/2WlTSFS - which is one I have) you could try adding a load and then seeing what current output you are getting at different engine RPMs.
Ref voltage, what difference will it make to you to know any open circuit voltage? put a meter on the leads that are running to the leisure battery and measure the voltage - that is the voltage you need to look at rather than a theoretical number.
Measure that voltage and the voltage at the starter battery and the difference is the voltage drop on the cable at that current. As the current changes, the voltage drop will change (more current = more voltage drop). If you know the gauge of the cable and the length, then you can work out the voltage drop at the current you are wanting to draw.
 

Markd

Full Member
Posts
719
Likes
408
@Derekoak
I'd have thought that 30A charge into a single battery was very respectable - indeed will lead acid draw that much anyway?
Mind you if you do change to lithium it will take that much and unless you've flattened it a couple of hours running should bring it back up nicely.
Ideally you'd want more than 6mm cable for that current the B2B will compensate for input voltage drop.
B2B to battery cable does need to be properly sized for current and length.

This may be what you have?

Screenshot_20201216-164650_DuckDuckGo.jpg
 
Last edited:

Derekoak

Full Member
Posts
475
Likes
322
Thanks Mark that may well be the alternator. At the moment I have an AGM 80ah battery it has taken 30 amps charge, i understood they take more than other lead acid batteries. Mind you with the Agm the current drops below maximum quite quickly about 15 minutes. 100 ah lithium will be a more sustained charge.
I understood the b2b made the lost volts less important but 2.5% loss seems slightly significant, but as the current drops the lost volts drop linearly. I have been testing my existing battery by deeply discharging it rather than not fully charging it when driving a distance I think.
 

Markd

Full Member
Posts
719
Likes
408
Fast current drop off is to be expected.
Deep discharge of AGM will certainly 'test' it - don't want to do it too often.
 

Derekoak

Full Member
Posts
475
Likes
322
If you have, or can borrow, a Multimeter with a Clamp for current (like this one for example - https://amzn.to/2WlTSFS - which is one I have) you could try adding a load and then seeing what current output you are getting at different engine RPMs.
Ref voltage, what difference will it make to you to know any open circuit voltage? put a meter on the leads that are running to the leisure battery and measure the voltage - that is the voltage you need to look at rather than a theoretical number.
Measure that voltage and the voltage at the starter battery and the difference is the voltage drop on the cable at that current. As the current changes, the voltage drop will change (more current = more voltage drop). If you know the gauge of the cable and the length, then you can work out the voltage drop at the current you are wanting to draw.
Bought one thanks wildebus
 

wildebus

Full Member
Posts
4,035
Likes
4,265
Something you need to remember to do with the clamp meter is to "zero" it before you use it each time. Easy to do ... hit the zero button :) the tricky thing (for me anyway!) is to remembering to do it!
I was using mine to check a 24-12V DC Converter and it seemed to be putting out too much current even when not in use when I was going around checking stuff after installation. Then I remembered the Zero button ... did that to recalibrate, measured again and much more as expected (y)
 

wildebus

Full Member
Posts
4,035
Likes
4,265
I was out in my Motorhome today and in readiness, I had let the Leisure Battery Bank (300Ah Lead Carbon) drop to 50% so I could check the B2B installation (this being the first proper trip since the new installation).

I thought I would post a graph which I think is quite interesting with the discussion on whether a B2B Charger is needed or if a simple Relay would suffice.

Some points on the setup:
  • The Voltage reading is at the input of the B2B, so takes into account any voltage drop of the cable
  • The cable run will be around 1.5-2M using 16mm2 cable
  • The current into the battery is a net 30A
  • The Fridge was running on 12V
1608234883495.png


As can be seen above, the voltage at the input of the charger is well below what you would want to see as a charging voltage.
The voltage drop from the 16mm2 cable is going to be pretty minimal (calculates to be no more than 5%, or 0.13V), so even if used super-fat cables with no drop, would not see it reach 14V anyway.
It would be interesting to see what effect the Fridge running had on the voltage. This would be pretty common of course, so is not a factor that should be discounted or compensated for in the calculations.
 

Markd

Full Member
Posts
719
Likes
408
That's quite revealing - is your fridge compressor or adsorption?
If the latter that's 20A to add to the LB load which because of the lower voltage will be probably be getting on for 40A.
Do you think your alternator is 100%

Not sure about 5% drop in 12v nominal system being 0.13v though?
Although I accept that with B2B its irrelevant but when I was doing some tickover fuel consumption readings on my car recently I didn't see anywhere near the same level of alternator voltage drop for a 50A draw.
 
Last edited:

wildebus

Full Member
Posts
4,035
Likes
4,265
That's quite revealing - is your fridge compressor or adsorption?
If the latter that's 20A to add to the LB load which because of the lower voltage will be probably be getting on for 40A.
Do you think your alternator is 100%

Not sure about 5% drop in 12v nominal system being 0.13v though?
Although I accept that with B2B its irrelevant but when I was doing some tickover fuel consumption readings on my car recently I didn't see anywhere near the same level of alternator voltage drop for a 50A draw.
It's a 3-way, so absorption fridge.
That voltage drop I quoted is not on the alternator, it is the estimated cable losses on the starter battery to B2B cable running through a voltage drop calculator (the 5% value actually looks much too high - the 0.13V looks right. I'll check another calculator!).
Update. Reran .... 0.88% . Not sure where the 5% came from first time!

I don't have a starter battery/alternator non-load voltage value when engine running, so don't know what that is (but in many ways it is not important - you want to know the performance of something when it's in use, not when it is idle).

I don't know how exadtly much current it is pulling when using the 12V supply. I might put a meter on there to see (and could check the manual as well I guess!) but if you make the assumption that the typical motorhome has an absorption fridge and that it will be running on 12V whenever engine on (both reasonable assumptions I think), then that is definitely something to be considered.
No idea if Alternator is 100%! Seems to keep the starter battery well charged

What this snippet of info is telling me at this point is if in this Motorhome I had a split-charge system that did not boost the voltage to the Leisure Battery, it would not be charging the Leisure Battery well at all!
Obviously a sample of one vehicle is not enough to really make a solid conclusion, but where in my VW LT I could run a relay (VSR/Cyrix) or B2B to charge the Leisure Battery bank, I would be unlikely to consider a Relay in my Ducato.
 
Last edited:

Markd

Full Member
Posts
719
Likes
408
O.88v drop is >5% of even 14.4v.
Either way the B2B will cope with that.
Definitely reinforces your point about split charge relay not being best way of charging Leisure batteries especially if load is high to a large bank like you have.
 
Last edited:

wildebus

Full Member
Posts
4,035
Likes
4,265
O.88v drop is >5% of even 14.4v.
Either way the B2B will cope with that.
Definitely reinforces your point about split charge relay not being nest way of charging Leisure batteries especially if load is high to a large bank like you have.
0.88%, not 0.88V ;)
I use this on-line calc - https://www.calculator.net/voltage-drop-calculator.html?
handy one as it has the table at the bottom to convert metric to AWG so saves time looking elsewhere to convert.
 

Philip Tomlinson

Administrator
Posts
5,258
Likes
11,764
I was out in my Motorhome today and in readiness, I had let the Leisure Battery Bank (300Ah Lead Carbon) drop to 50% so I could check the B2B installation (this being the first proper trip since the new installation).

I thought I would post a graph which I think is quite interesting with the discussion on whether a B2B Charger is needed or if a simple Relay would suffice.

Some points on the setup:
  • The Voltage reading is at the input of the B2B, so takes into account any voltage drop of the cable
  • The cable run will be around 1.5-2M using 16mm2 cable
  • The current into the battery is a net 30A
  • The Fridge was running on 12V
View attachment 90035

As can be seen above, the voltage at the input of the charger is well below what you would want to see as a charging voltage.
The voltage drop from the 16mm2 cable is going to be pretty minimal (calculates to be no more than 5%, or 0.13V), so even if used super-fat cables with no drop, would not see it reach 14V anyway.
It would be interesting to see what effect the Fridge running had on the voltage. This would be pretty common of course, so is not a factor that should be discounted or compensated for in the calculations.
Did the batteries reach full charge during this charge? You would want to see the starter battery voltage as it reaches the end of the absorption phase.
 

wildebus

Full Member
Posts
4,035
Likes
4,265
Did the batteries reach full charge during this charge? You would want to see the starter battery voltage as it reaches the end of the absorption phase.
No, still a way to go.
Just gone out and checked the Starter Battery voltages at different points ...
Running, no "extra loads" (so engine idling, no fridge, no B2B connected) - 14.28V
Running, Fridge on 12V, no B2B - 14.16V
Running, No Fridge, B2B Connected and outputting 33A - 13.44V
Running, Fridge on 12V and B2B outputting 33A - 13.29V

B2B outputing 33A - say 80-85% efficient, so pulling about 40A out the Vehicle system?
Seems quite a drop of voltage when the Load is increased? :unsure:
 

mfw

Full Member
Posts
1,359
Likes
1,735
Have to say i hate electrics and do find it boring and monotonous wish i could get my head around it and as far as batteries go just look for a decent ah on them

As much as i like viewing these threads i'm still clueless afterwards - mechanical stuff quite happy doing
 

Harryw

Full Member
Posts
112
Likes
116
No, still a way to go.
Just gone out and checked the Starter Battery voltages at different points ...
Running, no "extra loads" (so engine idling, no fridge, no B2B connected) - 14.28V
Running, Fridge on 12V, no B2B - 14.16V
Running, No Fridge, B2B Connected and outputting 33A - 13.44V
Running, Fridge on 12V and B2B outputting 33A - 13.29V

B2B outputing 33A - say 80-85% efficient, so pulling about 40A out the Vehicle system?
Seems quite a drop of voltage when the Load is increased? :unsure:
Is that just at tick over ? Does it get better at say 1k5 rpm?
I don’t think it unreasonable to expect a modern alternator and regulator to hold nearer the 14.2v with a 40a load.
 
Top