diy solar

diy solar

AGM batteries + inverter voltage drop to 10V on load

S

stawnasto

New Member
Joined
Jan 7, 2024
Messages
7
Location
New zealand
Hello everybody.
I have solar panel 200W in my caravan, I bought 3000W peak/1500W actual / pure sine Wave inverter to my caravan for my Coffe express (1250W) to do 2 coffe in the morning. I have now old acid battey which I going to replace now. I got 2 pcs secound hand AGM batteries:

Shoto 6-FMX-100B 12V 100Ah C10
25 C floating voltage: 13.38 V
Terminal hardware torque 9~11 NM
Charge current Max 20A

When battery are charge and I test them one by one doing coffe and my inverter shows voltage on full load 10.4 -10.00 (sometimes 9.99V) it jumping from 12.5 to 10V depend of coffee machine power usage...
Is it OK? In manual of inverter says I've voltage drop to 10.5V inverter stops, but actually working through all coffee preparing process.

Does AGM battery are ok? Or they are used too much?
Thanks for help

Photos:
 

Attachments

  • 17046856059865495572375458693509.jpg
    17046856059865495572375458693509.jpg
    93.3 KB · Views: 16
  • 20240108_161131.jpg
    20240108_161131.jpg
    143.4 KB · Views: 17
A bit on the high side to discharge them at 130+ amps individually. Even if together 65 amps is a bit much. Look like UPS batteries that may not like the high discharge rate.

Are they charged with just the float voltage 13.38? s/b about 14.4 volts until current drops to 1/2 amp per battery to call it full.
 
Actually I got them yesterday and I charge them few hours using battery charger, photo in attachment until show full charge, I bought today proper MPPT controller but didn't connected batteries to solar power, just wondering if batteries are good enqught for my coffe addiction...
 

Attachments

  • 20240108_182300.jpg
    20240108_182300.jpg
    73 KB · Views: 5
It seems like you're asking too much of the batteries and the wires. For the wires: are they 5mm diameter (about 4AWG) or 5mm^2 cross section (about 10AWG)? I mean only the conductors, not including the insulation. The size should be marked on the jacket.

Depending on the jacket, 4AWG can handle up to about 95A, while 10AWG is good to about 40A (depending on the jacket, again). Trying to pull 130A from a single 100Ah battery by itself is a lot to ask, especially an older one. Here's what I would do before giving up hope:

- Wire the batteries in parallel so you end up with a 12V 200Ah bank.
- If you're not using at least 4AWG (5mm diameter) wire, upgrade to that or something bigger, the bigger the better, you'll have less power loss to heat and less voltage drop.
- Charge them with a float charge (13.38V as you said should be fine, whatever the manufacturer recommends) for at least a day. Then you can be more sure they were fully charged before you try the coffeemaker.
- Try the coffee maker again, then let the batteries rest for several hours. Check the voltage then. You're trying to see what their resting voltage is after that single or double big draw is. It will give you some rough idea of capacity.
 
Those SH standby batteries typically have a maximum discharge of 0.5C, 50 amps per battery.
stawnasto said:
orginal cable what came with inverter
Click to expand...
Usually too small and questionable quality. Suggest 25m2 cable.

If the batteries are in good condition, fully charged and used in parallel, the voltage at the battery should hold above 12 volts for at least 30 minutes of coffee maker use.

Charge to 14.1 to 14.2 volts, 3hour absorbtion, float at 13.4 volts.
 
Hi
So I connect paraller my battery in caravan, I bought cable but 21mm2 was only available, I connect controler MPPT 30A Magic Series and set settings to AGM batteries, battery shows 70% capacity and I left for whole day and it charger it to 99%, I checked voltage on batteries and it shows 13.7v
I started doing first coffe, during coffe making voltage on battery on multimeter do not drop belowe 12v, on inverter lowest voltage show 11.5v, first coffe was done, but during secound inverter led light "fault" popup, I switch of and on inverter but during coffe making led light pop up and inverter stop... WTF ??

But any way I was able to prepare somewhere 2 coffee, I disconnect solar power and next day i checked voltage was 12.9 / 13v...

So battery are reasonable good? For secound hand one?

Some photos in attachment
 

Attachments

  • 20240111_163928.jpg
    20240111_163928.jpg
    111.5 KB · Views: 11
  • 20240111_163932.jpg
    20240111_163932.jpg
    97.7 KB · Views: 9
  • 20240111_163939.jpg
    20240111_163939.jpg
    276.1 KB · Views: 7
  • 20240111_163952.jpg
    20240111_163952.jpg
    239.1 KB · Views: 6
  • Screenshot_20240112_055650_Chrome.jpg
    Screenshot_20240112_055650_Chrome.jpg
    59.6 KB · Views: 8
Last edited:
Keep the solar on. Maybe a few charge cycles with proper voltage will help them.
Yes they are fine at zero cost and if two cups gets you through the day they are fine. Leave the solar on while you brew.

Hopefully they work a few months while you save and shop for a 200 Ah lithium battery.
 
mikefitz said:
Those SH standby batteries typically have a maximum discharge of 0.5C, 50 amps per battery.

Usually too small and questionable quality. Suggest 25m2 cable.

If the batteries are in good condition, fully charged and used in parallel, the voltage at the battery should hold above 12 volts for at least 30 minutes of coffee maker use.

Charge to 14.1 to 14.2 volts, 3hour absorbtion, float at 13.4 volts.
Click to expand...

@stawnasto

All of this. charging to only 13.38V is going to take as much as 48 hours to get batteries fully charged. Limit to 14.1V per this datasheet:


They are not likely to last long.
 
Thanks for help, I didn't get them for free unfortunately, I paid around 140usd for 2 pcs... but I can return them so just wondering if it worth to keep them or no... but looks like no...
Let's say full battery shows voltage 13.7v so after making one coffe and when battery rest voltage should show 13.7v again?
 
You must log in or register to reply here.

Similar threads

P
Voltage Drop On Batteries
Replies
15
Views
1K
philatio
P
F
Transfer switch LV cutoff settings and voltage drop under load
Replies
5
Views
622
furkidmom
F
Back
Top