my problem with charge 48v gel batteries . Please adivice

[mot1639]

HI all
first of all let talk about my solar equipments I have.
I have
1-4 x 250 W 38v (open circuit) 8 Amp
( I connect each two in parallel ) and then connect this two in series to have 48v system, ( when I test it with meter it give me 64v) which I think is ok.)
2- 4 x 12 volte gel batteries ( also same I make series and parallel connection to have 48v gel batteries, ( now when I chick this new batteries with meter it shows me 52v which mean it almost full) the total power now should be 9600w (200A * 48V)
3- 1 x Mppt controller

** for connection I connect the solar panel to mppt and form mppt to gel batteries.
** now before I start charge the batteries I connect the batteries (48v) to 120 AC inverter to switch ON 1000W light , and yes the light keep work for 7 hours . and after 7 hours it inverter start beep that indicate there no enough power to switch on the light .. and thin the inverter switch off .

when I chick the batteries it show me 44v rather than 52v when it is new ..

now I need to charger it , when I put my solar panel in clear view of sun and make mppt start charge .. it show me in mppt screen it start charging the gel batteries and the output power for charging is 700w and the current is almost 14-15A.. which is great in my case and enough for me ...

but after 30-45 minutes it decrease to 4-5A and the power 100-200W ..

I again discharge the batteries and agian try to charge it in different time of the day and yes it start with 12-15 A 700 w and thin after 30-45 minutes it start to decrease to 4-5 A 100-200W .

I use different controller it give me same reading of power and current ..


there no other connection in my system it is direct connection , I only use small dc breaker to disconnect the pv cable from the controller ..

where is my problem , it is batteries or controller ????? please advice , i already spend more than 4000$ in this system , again please advice ??


regards

[inetdog]

I again discharge the batteries and agian try to charge it in different time of the day and yes it start with 12-15 A 700 w and thin after 30-45 minutes it start to decrease to 4-5 A 100-200W .

I use different controller it give me same reading of power and current ..


there no other connection in my system it is direct connection , I only use small dc breaker to disconnect the pv cable from the controller ..

where is my problem , it is batteries or controller ????? please advice , i already spend more than 4000$ in this system , again please advice ??

Three problems:
1. GEL batteries cannot be charged as rapidly as either FLA or AGM without suffering damage. A reasonable charge rate would be C/20, or in this case 10amps if you really have 200AH of battery. But you stated that you have four 12V batteries in series and parallel to make 48 volts. Either you have 8 batteries, or they are just in series. What is the AH capacity of the individual batteries, and how many do you have?
2. The charge controller is set to charge at the maximum available current (Bulk stage) only until the battery voltage reaches a preset level. At that point the CC will switch to constant voltage and the current will taper off as the battery continues to charge (Absorb stage.)
3. You description of the panel output is a little confusing. The open circuit voltage (Voc) of 38 is OK, but when you measure the two in series with a meter, you say you get 64 volts instead of 76 volts. Do you mean that this is the Vmp voltage while actually charging?

It is possible that the Absorb voltage is set too low for your GEL batteries. Or there may be a problem with their charge acceptance ability.

More information please.

[mot1639]

Three problems:
1. GEL batteries cannot be charged as rapidly as either FLA or AGM without suffering damage. A reasonable charge rate would be C/20, or in this case 10amps if you really have 200AH of battery. But you stated that you have four 12V batteries in series and parallel to make 48 volts. Either you have 8 batteries, or they are just in series. What is the AH capacity of the individual batteries, and how many do you have?
2. The charge controller is set to charge at the maximum available current (Bulk stage) only until the battery voltage reaches a preset level. At that point the CC will switch to constant voltage and the current will taper off as the battery continues to charge (Absorb stage.)
3. You description of the panel output is a little confusing. The open circuit voltage (Voc) of 38 is OK, but when you measure the two in series with a meter, you say you get 64 volts instead of 76 volts. Do you mean that this is the Vmp voltage while actually charging?

It is possible that the Absorb voltage is set too low for your GEL batteries. Or there may be a problem with their charge acceptance ability.

More information please.

first of all , thank you for your replay ...

1. GEL batteries cannot be charged as rapidly as either FLA or AGM without suffering damage. A reasonable charge rate would be C/20, or in this case 10amps if you really have 200AH of battery. But you stated that you have four 12V batteries in series and parallel to make 48 volts. Either you have 8 batteries, or they are just in series. What is the AH capacity of the individual batteries, and how many do you have?

sorry , I have 4 batteries 12v 200A each , I connect it all in series , sorry not in parallel , sorry I miss typing . the total is 48V , 200A.


2. The charge controller is set to charge at the maximum available current (Bulk stage) only until the battery voltage reaches a preset level. At that point the CC will switch to constant voltage and the current will taper off as the battery continues to charge (Absorb stage.)
there are no setting for this type for MPPT , it should work automatically , but only setting I can do is to select the battery type. which is GEL battery

3. You description of the panel output is a little confusing. The open circuit voltage (Voc) of 38 is OK, but when you measure the two in series with a meter, you say you get 64 volts instead of 76 volts. Do you mean that this is the Vmp voltage while actually charging?

sorry again, it is 34 not 38, the total is 68 , it give some time 64,63,65 depend in the sun clearance . without any load ..

FYI . regards and THANKS

[inetdog]

2. The charge controller is set to charge at the maximum available current (Bulk stage) only until the battery voltage reaches a preset level. At that point the CC will switch to constant voltage and the current will taper off as the battery continues to charge (Absorb stage.)
there are no setting for this type for MPPT , it should work automatically , but only setting I can do is to select the battery type. which is GEL battery

There will be voltage set points that correspond to the GEL setting. Whether they are correct or not for your particular batteries is an open question. Does the CC manual tell you what voltage settings result from putting the switch in the GEL position? Can you tell us more about the brand and model of the batteries?

I am not convinced that the CC is not behaving exactly as it is supposed to based on the voltage it is seeing at the battery terminals.

Also, even with an MPPT controller, 64 volts open circuit is a little low for charging a 48 volt battery bank.
For Voc = 64, the Vmp is going to be close to 51 volts and a 48 volt bank needs a charger capable of 56 to 62 volts. Since the MPPT CC cannot convert the input voltage to higher voltage, your panels are really not compatible with a 48 volt bank. You would need to have three in series to be able to consistently use the maximum amount of power from them.

[Mike90250]

When the batteries are 80% full, they still need at least 40ah pumped into them. The first 80% happens at BULK rate, full power from the PV array. The last half (ABSORB) will happen at a much slower rate, and at your 5A absorb rate, that will take at least 8 hours of absorb, if it works at 100% efficiency.
But designing a system properly is never done, so that's why this forum stays so busy - how to correct design deficiencies and incorrect part selection.

Corrective action would be non-GEL batteries (Flooded or AGM) and
increased PV Pmax array voltage to at least 80V.