Charging your Leisure Batteries on the move.

wildebus

wildebus

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There is a lot of discussion of B2B Chargers, and their various merits or otherwise over the basic Relay type of Split Charger.

Next week I plan to do some testing on these to obtain a profile of just what kind of charge they provide and what the users can expect when they use a B2B or when they use direct alternator type charging through a relay. This might help understand what size (in Amperage) of B2B is suitable and the time they can expect a battery to recharge (and what the impact is for differing sizes).

I thought I would first post my proposed test setup so if anyone would like to suggest any improvements (within the kit I have available!)


Power Source.
Now I don't intend to drive around for hour after hour to have the alternator running, or idle the van engine all day, so I will be using a 120A Charger as the 'alternator', set at an output voltage that is typical of that presented to a B2B or Relay by the alternator AND taking any voltage losses in mind at the end of a typical 4 Metre run of 16mm cable - so probably I will set the charger to around 13.9V (but will check the cable loss charts to confirm)

This Power Source will be cabled up to the charger being tested. I will also connect a 100Ah fully charged battery in parallel between Power Source and Charger to act as a Pseudo-Starter Battery to simulate the same kind of actual setup you would have in a vehicle.


Leisure Batteres.
This test will be limited by the battery bank I have available. My plan is to start each test with my 380Ah AGM Battery Bank discharged to 50% SOC, so as low as you would want to go on Lead Acid usually and will also give the best test for the chargers as will cover the full charging range from Empty (in usuability terms) to Full.
All loads will be minimied during the test, so lights will be off, no heating, fridge will be off, etc. I will have a load in terms of monitoring hardware. These will be the same for all chargers. I'll also have the Solar MPPT Charger turned off so that doesn't skew anything.


Battery Chargers.
The point of the test will be to check different options in terms of charging methods and capacities. It is not to compare different models and makes of equivalent specifications.
These are the systems I have lined up to evaluate:
  1. 100A HC Cargo VSR - Essentially just a battery connecting device, but I will run the "alternator" though this for completeness.

  2. 40A Redarc BCDC1240 Battery to Battery Charger - This is a unit I have been running in my Camper for a while.

  3. 30A Ablemail Battery to Battery Charger - This is a new unit to me but looks promising. I have this for evaluation following a meeting yesterday with the owner of Ablemail and though I would add this to the test portfolio.

  4. 20A Victron Mains Charger + 500W Inverter - This will be an extended test on the "Inverter as a Split Charger" idea I posted about before, testing the concept in an identical way to the B2Bs and VSR.

So the above will provide a good range of current capabilities as well as different approaches.
As mentioned, for each Charger the testing will start with the Battery Bank at 50% SOC as reported by the Victron VRM and will end when the VRM reports the Battery Bank at 100% SOC.
This will be the target, but it is possible some chargers will never get the battery to 100% due to voltage limits, so I will also look at a secondary target of maybe -5Ah or -10Ah from full to be able to compare (seeing this potential sitution is in fact part of the reason for testing)


I also have a Control Benchmark to compare each result as a comparative.

This is the chart of a 95A Mains Charger recharging the same bank from 50% to 100%.
This took 8 Hours. How long will a 20A, 30A or 40A charger take? This will be interesting to see :)


So that is the plan. I would be interested in comments and if there are any suggestions for the testing, or if anyone sees an issue with the test setup?
(Note that this test will be carried out in my campervan so ambient temps could vary which I cannot control of course)
 
the only problem i foresee is your battery bank starting point and the condition of the battery's how do you determine when they are at 50% and after every discharge they might lose a bit in their capacity for charging

rab
 
rab126 said:
the only problem i foresee is your battery bank starting point and the condition of the battery's how do you determine when they are at 50% and after every discharge they might lose a bit in their capacity for charging

rab
Click to expand...
As I said ... "for each Charger the testing will start with the Battery Bank at 50% SOC as reported by the Victron VRM and will end when the VRM reports the Battery Bank at 100% SOC."
The monitor also records the amount of Ah - at 50%, the battery will be -190Ah below the starting point (set at 380Ah). I'll be making a note of that data as well as a cross-check.
The battery fluctuation in capacity between individual charges will probably be less then the fluctuation in capacity due to a change in battery temperature I would say so and would be within the same level of difference between different examples of the same charger, so just noise. (my batteries have had just 15 cycles carried out of the design limit of 400, so still in very good condition)
 
I’ll echo the above couple of posts, especially now I do have a new 30a B2B and also new batteries coming on Tuesday.
 
I'll watch with interest as I also have the 40amp Redarc.
 
First test will probably be either the Redarc 40A or the 100A VSR - not decided yet :)
Spent today bringing the SOC down in readiness - had an electric radiator on for the last 7 hours and got it down to 53%. I'll finish the drop to 50% in the morning and hopefully start the test once redone the cabling to suit.
 
trevskoda said:
Should the voltage be 14.4 at full charge before going back to a float of 13.7
Click to expand...
Should it? Well it depends on the battery spec but generally I would say yes, ideally, for most lead acid.
First stage is bulk/CC - where the current is as much as can be delivered and voltage builds up; Second stage is absorption/CV - where the voltage stays at the top voltage (so 14.4V typically) and current starts to reduce; Third stage is float - where voltage drops and current is just a trickle.
Is there a specific reason for this question, Trev?
 
First Test.
Carried out the first test today. Decided to do the VSR first in fact.
I checked the VSR and it is rated at 140A, so I thought I would up the power in to 120A instead of the 100A Planned.

Opps. The VSR, despite being a 140A version, didn't like running at that current and after around 25 minutes cut out for a minute, then came back, the cut out again 5 minutes later. Decided to abort the test, set the maximum input current to 95A (which is what I usually have it set to) and restarted the test a couple of hours later (needed to get the batteries back to 50% SOC again before I could restart the testing)

I'll post all the results together at the end of the testing, but quick conclusion is the VSR charged the battery to around 95% in 8 hours; It will never totally charge the battery due to the too-low charging voltage, but is an OK solution if you have another way to 'finish the job' on a regular basis.
(the actual charging profile was NOT what the typical battery manufacturer would recommend.)

Also bear in mind that IF you had a 100A alternator and were pushing that current into the Leisure Battery, you would need a big battery bank to make that ok (the general recommendation is no more than 20% Charge - eg 20A max for every 100Ah of battery). It is something to keep an eye on with VSRs (B2Bs can be chosen by size to match the charging need, of course).

Next test probably Thursday and will be the 40A Redarc B2B. The B2B Tests will be, I think, a lot more interesting.
 
wildebus said:
Should it? Well it depends on the battery spec but generally I would say yes, ideally, for most lead acid.
First stage is bulk/CC - where the current is as much as can be delivered and voltage builds up; Second stage is absorption/CV - where the voltage stays at the top voltage (so 14.4V typically) and current starts to reduce; Third stage is float - where voltage drops and current is just a trickle.
Is there a specific reason for this question, Trev?
Click to expand...

Also depends on tempearture, 14.4 is at 25C so any deviation from that will raise or lower it, so any comparisons should be done at the same temperature to get consistent results, including the discharge down to 50%
 
PeteS said:
Also depends on tempearture, 14.4 is at 25C so any deviation from that will raise or lower it, so any comparisons should be done at the same temperature to get consistent results, including the discharge down to 50%
Click to expand...
I've already mentioned I am not in control of the weather.
 
Will be interesting Dave although I have already proved it in our van for us but I didn’t fit a new vsr just whatever it was in the van. For us the B2B sorts things if we keep moving. Doubt our batteries will be fully charged more than once or twice a year though
 
Ok, just for thick me could you define what b2b and vsr mean? I am in awe of you @wildebus and keep reading your technical posts in the hope that some knowledge will trickle in! If you can explain, I can maybe identify what we have or at least ask someone!
Thanks Ruth
 
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