Couple of Questions About Charging Requirements in Relation to Resistance.

[LuckyLuke]

Hey guys,

Just a quick question regarding charging and charge controllers. This might seem like a silly question since I'm still a bit green in this field.

When measuring how many amps are going into the battery bank, can the size requirement of an array change depending on what kind of battery you are charging? For example: flooded, AGMs, gels, and lithium.

Let's say If there is a slight battery resistance (depending on the type of battery) and you have an array capable of 40amps at 24v and the charge controller displays 20 amps going into the bank, in bulk mode, Is the battery bank that needs at least 27 amps according to the 10% - 20% rule not going to charge properly?

Thanks in advance,

Luke

 

[MisterSandals]

charge controller displays 20 amps going into the bank, in bulk mode, Is the battery bank that needs at least 27 amps according to the 10% - 20% rule not going to charge properly?

I think this question answers itself.

 

[AmpD]

A missed opportunity for education.

While the answer is in the question for newcomers trying to understand bank sizing and how everything works together this could have been a golden thread of knowledge.

I’ll keep digging for the nuggets of wisdom.

 

[DougfromdaUP]

The size of your array depends on your energy needs, not just battery size.

Lithium batteries work well at low charge rates, so any charge rate below the maximum is fine.

 

[AmpD]

I get that usage, pv input, and bank size all correlate.

What I don’t get is why a 50v array at 8amps would be bad for a 24v 500ah bank. Lets go with 500w daily usage at 20-25w constant load.

In another thread it was mentioned that a 20a charge rate was killing some lifepo4 batteries that needed over 100a charging rate.

 

[DougfromdaUP]

I’ve never heard anyone claim that LiFePO4 batteries need a high charge rate, and that a slow charge will harm them. I believe that may be true of lead batteries.

 

[MisterSandals]

I’ve never heard anyone claim that LiFePO4 batteries need a high charge rate, and that a slow charge will harm them.

Agreed. I am not sure how i came up with my words in post #2. I am eating crow for that.

I've been the most conservative LiFePO4 charger I've known, pretty much from 2019. And very rare i charge over .1C, Victron 100/30 capped off at .05C (20A for 416Ah) in my RV with super results.

As for lead acid, i have been trickle charging Sprinter engine battery at 2A 24/7 for 15 years. First battery lasted 9.5 years doing that. Never heard of a minimum there either.

 

[seneysolar]

I’ve never heard anyone claim that LiFePO4 batteries need a high charge rate, and that a slow charge will harm them. I believe that may be true of lead batteries.

From my experience, lead acids dont seem to care. Trojan FLA recommends 13% of C1 rate. As a target for most efficient charging sure, but a requirement no. Im going on 7 years on this set of L16s charging at 5% C1 max.

When we are capacity checking Concorde VRLA at work, they want 10% to recover from deep discharge on the bench, but when installed in the aircraft the same 43AH 24V battery will see 200-250A when the generator is brought online after engine start... nothing bad happens