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LifePo4 Charge Rate


CDL
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Hi guys,

I have a Victron Quattro mated to Canadian Solar panels and some second life LifePo4 batteries with their own BMS' supplied with the batteries. The batteries are in two banks of a nominal 180 amp hours each (one bank is in fact about 200 amp hours), connected in parallel. Using the Victron Remote Control interface, DVCC allows one to set a maximum charge current. I am getting conflicting advice as to whether a maximum charge current should be used with these batteries and if so, what that maximum charge current should be. I have been told anything between 120 A and 60 A. Yet reading online, it seems that there is no need to limit the charge current.

Is anybody able to provide any sensible input or advice here?

Many thanks in advance.

The other question that I had is whether it is possible to set the cut off voltage (low-voltage warning) for the battery arrays using the Victron Remote Control interface? I have looked through all the settings, including DVCC and ESS and cannot find anything. I am wondering whether I am looking in the wrong place… If anyone knows where I should be looking, I would appreciate the input.

Hope everyone is surviving the lockdown!

 

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Actually, I had to go and look for them after your post above 🙈 (lekker dom) and then went to find them at the distributor's website. See attached. I see the maximum charge rate that is recommended is 65 A. That is for one battery array. Presumably if I have two battery arrays, then presumably I should set the maximum charge rate on the inverter to 130A? Is the logic correct?

Revov-LFP200C48VN-C.pdf

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1 hour ago, CDL said:

Actually, I had to go and look for them after your post above 🙈 (lekker dom) and then went to find them at the distributor's website. See attached. I see the maximum charge rate that is recommended is 65 A. That is for one battery array. Presumably if I have two battery arrays, then presumably I should set the maximum charge rate on the inverter to 130A? Is the logic correct?

Revov-LFP200C48VN-C.pdf 1.35 MB · 2 downloads

My LFP cells came with a recommended charge/discharge current as well and this is what I used which was significantly less than the maximum in order to improve the life of the cells.

The normal recommendation is to do 0.2C of the battery so 80 Amps barring any manufacturer recommendations.

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Thank you. Following your advice I spoke to them a few minutes back. They have suggested that I can use 120 amp as the charge current maximum for charging the batteries through all three stages in the normal course of events. They do suggest though that if I want to balance the batteries (if they go out of balance at any point in time) that I should then use 60 A maximum to charge them and then float them for a period of about 24 hours, which should then bring them back into balance. Apparently that this should not be required very often at all.

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6 hours ago, CDL said:

They have suggested that I can use 120 amp as the charge current maximum for charging the batteries through all three stages in the normal course of events.

Well, as @20VT already stated the recommended max charge current is 65A. We can be sure about one thing, if you almost double this to 120A it will not make them live longer...  But now when I read your first post again you say you have 2 banks in parallel so doubling the charge current isn't that weird. Is it 24V system?

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I spotted with my 120ah lifepo4 setup that they are happy at 54.2v with about 30amps of charging, this with the mppt.  In the morning. Bulk charge is set at 60amps max for 1h30m but it doesn't get close to that max, with float it's set at 53.8v and it runs between 10 and 20amps till it's full. 

@CDL what size array and MPPT are you running? You say you got 2 sets of the 200ah revolve units? 

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11 hours ago, RikH said:

Well, as @20VT already stated the recommended max charge current is 65A. We can be sure about one thing, if you almost double this to 120A it will not make them live longer...  But now when I read your first post again you say you have 2 banks in parallel so doubling the charge current isn't that weird. Is it 24V system?

The system is 48V. The distributor says doubling the charge rate is fine because the capacity is double.

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11 hours ago, Gerlach said:

I spotted with my 120ah lifepo4 setup that they are happy at 54.2v with about 30amps of charging, this with the mppt.  In the morning. Bulk charge is set at 60amps max for 1h30m but it doesn't get close to that max, with float it's set at 53.8v and it runs between 10 and 20amps till it's full. 

@CDL what size array and MPPT are you running? You say you got 2 sets of the 200ah revolve units? 

About 9.5kw nominal rating of panels - on a good day will push 8.5kw. MPPTs are Victron. Yes re the batteries. One set is 180ah the other 200ah. Actual, not rated.

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2 hours ago, CDL said:

About 9.5kw nominal rating of panels - on a good day will push 8.5kw. MPPTs are Victron. Yes re the batteries. One set is 180ah the other 200ah. Actual, not rated.

Nice. So you got the array to charge that size. I will say adjust your charging amps down about so that you don't push the batteries to hard, will shorten the life of your batteries. It's a bit of a playing game and adjusting till you find the rite spot for charging. 

Like with my setup, I'm running a DIY 120ah lifepo4 with Microcare 60a MPPT with 2.9kw array and say on a good sunny day the lifepo4 setup is fully charge between 10am and 11am. The last 20ah of charging the mppt runs between 10 and 20amps amd this helps the cells to level out. Will see when i got my second lifepo4 setup running and connected second mppt and with winter time.

What size victron mppt's is it? 

 

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The MPPTS are rated at a maximum of 70A on the photovoltaic side and 100A on the battery side. There are two of them. The panels are set up East/West (a bit below 5 kW in each direction), which works well in this application because it means we start generating earlier and we keep generating later and we have a more even power generation curve. Mostly, the batteries don't receive more than between 60 and 80 A (in total in respect of both of them together thus 30 and 40 each); a lot of the time it is a bit lower as well. It all depends upon solar conditions and how much is being used by direct consumption within the household. But occasionally it does rise above 80 A and sometimes even to over 100 A (more common in midsummer than this time of year). Absorption on the batteries runs at around 55.6 V and float at around 54.6 V. When the weather is good, the batteries tend to get to absorption around late morning/lunchtime. So they will usually spend an hour or two in float before we start to move into late afternoon/early evening and the power generation drops off. Overnight, with normal usage the batteries tend to drop down to about 52 V. I pretty much only run the heat pump during the day and get the water very hot (11 AM to 3 PM); I don't often need to run it in the early hours of the morning to heated up again but if I do, the batteries usually have enough capacity to handle it and we will go down to around 50 V. Obviously, this is the rough rule of thumb and it is variable from time to time, depending upon who is using what when, et cetera.

Most days the household consumes around 30 kWh produced by the solar panels; a little over half of that goes to direct household consumption and the rest goes to recharging the batteries. Provided the weather is good, all of that is generated by the panels. We don't need Eskom at all when the weather is reasonable. Even if it is a little bit overcast, we pretty much get away with what we need from the panels.

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