B2B Maximum Charging Rate

Bustup15

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I'm a bit confused reading recent threads about lithium and charging rates.

Each battery manufacturer seems to quote a maximum charging rate in A. Typically 45-50A although I have seen larger batteries with up to 100A quoted.

Does this mean a Sterling B2B 1260 (60A) will over charge those rated at less than 60A or does the inbuilt controller of the battery prevent this?

All my on board kit such as solar and charger have lithium profile options.

TIA
 
Sep 29, 2019
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Not an answer but I think that 60A is the input and not the output amperage of the 1260 which would thus be lower. Also posting as I'm interested in answer....
 
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As far as I know, most LiFePO4s will take almost whatever you throw at them. Check the manufacturer’s website for max charge current and call Charles Sterling to make sure. He is very helpful, if direct.

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Tombola

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Most Lifpo4 will take 100amp input and some more .
The sterling @ 60 amp will be enough and will also know when to cut out the charge if required.
 
Sep 29, 2019
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I believe the BMS is the limiting factor for charging.

However if you have two then you can double it. The Ecotree for instance limit to 50amps but that’s each, so two batteries will take 100amps.
 
Jan 19, 2014
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The way I look at that is the battery with its bms presents a load to the charger and therefore a resistance, and it will be that that determines the current that will flow..in other words a designed in feature
As you say most lithium batteries of the drop in replacement type have a designed /prefered rate..my TN Batteries state .2c but are capable of up to 50 amps..with most of the lithium ion charging profile voltages 20 odd amps is what they will take but if you were to up the voltage that would increase the charge current..(myTN batteries are rated at 110amp hours and therefore charge at a little over 20 amps per battery on the bulk phase of the charging cycle )
So even though I have a Stirling 60 amp battery to battery I only see around 45 amps flowing (two batteries in parallel ).. but if they were trying to take a larger current the battery to battery charger would be the limiting factor in the max current flow..
Thats the way I'm seeing it pan out anyway..
Andy..

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May 7, 2016
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I believe the BMS is the limiting factor for charging.

However if you have two then you can double it. The Ecotree for instance limit to 50amps but that’s each, so two batteries will take 100amps.
I wouldn’t trust my BMS to stop the overload, the monitoring relates to voltages and temperatures but nothing is said about Amps. I think the battery resistance remains very low until the battery reaches fully charged so that may not limit the overcharging either. I would check with the battery manufacturer before installing a B2B capable of more Amps than the battery can cope with.
 
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Bustup15

Bustup15

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Thanks for all the replies - andy63 matches what I thought but wasn't 100%. I have emailed both Sterling and Ecotree and will update if they provide any other info.
 
Apr 27, 2016
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The way I look at that is the battery with its bms presents a load to the charger and therefore a resistance, and it will be that that determines the current that will flow..in other words a designed in feature
The first stage of charging (bulk) is in constant current mode. The voltage increases to whatever is necessary to push the 60A current into the battery, until it reaches the absorption voltage. So unless the BMS regulates the current or trips out, 60A is what goes into the battery.

There is a setting (on my B2B at least) for half of that value, ie 30A. A bit of a waste if you've already bought the B2B and battery, but no need to throw it away. But ready for a second battery in the future, I suppose.

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Jan 19, 2014
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So unless the BMS regulates the current or trips out, 60A is what goes into the battery.
I have the Stirling 60amp battery to battery charger.. when it charges my two 110 amp hour lithium batteries in its bulk stage it delivers around the 45amp mark not the 60 amps its rated at...that seems to tie in with the preferred charging rate of the TN batteries of 0.2C as stated in the data sheet .. it does say they can accept up to a 50 amp charge per battery and I assumed that in order for that current to be delivered the voltage during the bulk stage would have to be allowed to increase and rise beyond the pre set voltage at which the absorption phase begins for the lithium profile of that charger
Andy
 
May 7, 2016
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I have monitored the charging of my Relion Li battery. The voltage rises slowly as the charge flows in whilst the amps remain constant. After reaching about 14V the voltage starts to rise more rapidly and when it gets to 14.6V the amps fall off a cliff. The battery is full.
 
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Bustup15

Bustup15

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Update from a very helpful Rob @ Ecotree.

Manufacturer advice was although smaller batteries with 50+ A max charge rate would be ok BUT potentially may impact on the battery life by upto 10%. No danger as the integral BMS would prevent any substantial impact or damage.

2 batteries perfectly OK as the charge is split between them and therefore kess than the 60A.

1 larger battery such as the 210Ah also ok as that has max charge rate of 100+A.

Suggested to use a clamp meter to measure true amps at battery if no other metering present as it may be there is not 60A present at all and if so 1 of the smaller 100 or 110Ah batteries would be perfectly ok.

Hope this helps others.

And there is a FUN discount of 10% available.


Neil

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Apr 27, 2016
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I have the Stirling 60amp battery to battery charger.. when it charges my two 110 amp hour lithium batteries in its bulk stage it delivers around the 45amp mark not the 60 amps its rated at...that seems to tie in with the preferred charging rate of the TN batteries of 0.2C as stated in the data sheet .. it does say they can accept up to a 50 amp charge per battery and I assumed that in order for that current to be delivered the voltage during the bulk stage would have to be allowed to increase and rise beyond the pre set voltage at which the absorption phase begins for the lithium profile of that charger
At the point where it's charging at 45A, I guess that the voltage has increased to the set voltage limit of the charger. Is that right?

For a proper lithium battery charger profile, the full 60A will only be applied until the voltage limit is reached (technically called the compliance voltage), then it should stay at the voltage limit until it is fully charged and the amps drops to a predetermined level.
I have monitored the charging of my Relion Li battery. The voltage rises slowly as the charge flows in whilst the amps remain constant. After reaching about 14V the voltage starts to rise more rapidly and when it gets to 14.6V the amps fall off a cliff. The battery is full.
Is this charging from a Sterling B2B, if not what type is it? Is the constant amps value what you would expect as the full output of the charger?
 
Jan 19, 2014
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At the point where it's charging at 45A, I guess that the voltage has increased to the set voltage limit of the charger. Is that right?
Cheers for getting back 👍
I've never seen my Stirling battery to battery deliver more than 45 amps to the two batteries..
I thought that was as much as the batteries would accept at the voltages they were charging at..the recommended charge rate for my TN batteries is 0.2C and I thought that 45 amps appeared to be in order for two batteries in parallel..
It deliveres that 45 amps until the last 15 20 min of charging when the current drops fairly rapidly to zero current flow..
The Stirling has a lithium charging profile and that's selected on mine..
The only thing I'm not sure about and your reference to voltage has got me thinking about , ... I should check if running the battery to battery with the solar disconnected.. as it will be putting a voltage on the batteries ..
Ill look into that..
Cheers
Andy
 

DBK

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Cheers for getting back 👍
I've never seen my Stirling battery to battery deliver more than 45 amps to the two batteries..
I thought that was as much as the batteries would accept at the voltages they were charging at..the recommended charge rate for my TN batteries is 0.2C and I thought that 45 amps appeared to be in order for two batteries in parallel..
It deliveres that 45 amps until the last 15 20 min of charging when the current drops fairly rapidly to zero current flow..
The Stirling has a lithium charging profile and that's selected on mine..
The only thing I'm not sure about and your reference to voltage has got me thinking about , ... I should check if running the battery to battery with the solar disconnected.. as it will be putting a voltage on the batteries ..
Ill look into that..
Cheers
Andy
I think you're over-thinking it. :) The B2B is going to be doing its stuff while driving and unless massively discharged the batteries will be topped up in an hour or so. Solar isn't going to provide a huge amount over such a short period and won't have any significant impact, especially if your driving is at the start of the day and not at noon. :)

You could disconnect the solar of course but in the real world I can't see it making any impact unless you forget to turn it back on when you stop. :)

You could install a sort of reverse split-charge relay which disconnects the solar when the engine is running but I think life is complicated enough with this sort of thing. :)

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May 7, 2016
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Is this charging from a Sterling B2B, if not what type is it? Is the constant amps value what you would expect as the full output of the charger?
It is a Votronic VCC1212-45 and I have set it back from the maximum charge but it puts out a steady 35A+ which is plenty for my useage.
 
Sep 29, 2019
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On mine which is a 30amp Votronic I get 30 amps plus whatever the solar gives which this time of year, isn’t much.

Max I have seen testing on the drive is 35amps.

Is your alternator capable of the full 60 amps?
 
Jan 19, 2014
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Solar isn't going to provide a huge amount over such a short period
Cheers John.. its just autorouters point about what my battery to battery should be delivering.. it doesn't tie in with what I've been seeing... it was the voltage the solar would be applying to the leisure batteries..I thought that may be having an effect on the ability of the battery to battery to deliver a full 60 amps during the bulk phase of the charge..ie because its seeing the solar voltage....which is what autorouter is saying it should be doing..
It's never exceeded the 45 or so amp mark any time I've been taking any notice..and thats when the batteries are ready for a charge..
So I was just giving it a bit thought..
Andy..

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Sep 23, 2013
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Is your alternator capable of the full 60 amps?
This is a point well worth considering. Lithium batteries will pretty much absorb whatever you chuck at them, so a B2B charger can have a dual purpose. Not only does it boost the charge rate over a normal split charge relay system, but it also applies a maximum charge rate. An alternator normally expects to provide its maximum output for a very short time after the engine is started, as the charging rate falls off relatively quickly with lead acid batteries. But with Lithium, the B2B charger will keep drawing its rated current until the batteries are fully charged. If you start the engine on a rainy night, with headlights , heater fan, windscreen wipers etc all drawing power in addition to a B2B running at full chat & if you then only drive at low revs, the alternator may not get enough cooling air to run continuously at full rated output.

So the B2B must be sized with two criterea in mind. What it the maximum the batteries can safely absorb without limiting their life & how much can the alternator continuously provide without overheating, especially at low revs?
 
Sep 4, 2020
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Just to add to the point on alternators, if there is only one figure given for the rated Amps this is at 6000rpm so some consideration is needed for idle speeds. Some state two figures, this is normally Amps at 1500rpm and 6000rpm
 
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