Battery voltage fluctuates during charge, normal?

[Handmade Matt]

Hi.
I've just introduced myself in the new members area and would like to jump straight in with this question.
I have an off grid set up of 380watt array with 250ah 12v battery bank and an MPPT controller.
It's mainly to run LED lights and then laptops when we can.

As the controller charges the battery I have my voltmeter connected to the terminals to watch the progress.
Some funny thing happen. It will climb, 12.51 -12.52 - 12.53 etc and then it will decline again 12.53 -12.52 -12.51 etc.

It will then climb up higher than 12.53 and go again... It's now reading 13.10 but has gone as high as 13.15.

Is this normal?
Is it just the individual cells in the batteries "sharing" the power out and equalising a bit fo you think?
It's obviously not a problem, I am just curious.

Many thanks.

[Wy_White_Wolf]

I've only seen that with PWM controlers when the batteries are fully charged. It's the shunt turning on/off. What brand/make is your controller?

WWW

[Sunking]

Assuming it is a 3-stage charger and the stage voltages are set correctly you will see the voltage climb up to around 14 volts, then fall back to about 13.5 volts when the battery is fully charged. First thing in th emorning depending on how deeply you discharge the battery it should start out around 12. 4 volts and climb as it charges.

[Handmade Matt]

My charge controller is a cheap Chinese unit bought on eBay.
I've already decided to send it back, it's pretty yucky. You can see it here:
http://www.ebay.co.uk/itm/2610074254...#ht_6481wt_986

It claims to be MPPT but I'm doubting it already.
It's putting out less amps than it's getting in.

I've just bought (under advice from a friend) this unit:
http://www.ebay.co.uk/itm/3006809817...#ht_1740wt_986
It's German made (Steca) and seems to be much better and will allow room for me to expand my array.

[Sunking]

It claims to be MPPT but I'm doubting it already.
It's putting out less amps than it's getting in.

That is a dead giveaway it is not MPPT

[Mike90250]

... It claims to be MPPT but I'm doubting it already.
It's putting out less amps than it's getting in......

Or the battery is charged above the BULK setpoint, and does not need the boost.

[Handmade Matt]

Or the battery is charged above the BULK setpoint, and does not need the boost.

The unit states that it's full charge point is 13.7 and I've not reached that all day.
I've ordered the Stecca, it should do the trick.

[Sunking]

The unit states that it's full charge point is 13.7 and I've not reached that all day.
I've ordered the Stecca, it should do the trick.

13.7 is a Float Level, not bulk or absorb.

[Handmade Matt]

It seems to be a very basic charger.
Here's the data sheet:


It doesn't mention any difference between bulk, absorb or float level as far as I can see.

[Sunking]

Afraid it means you got what you paid for. A good MPPT controller will allow you to set the Bulk, Adsorb, and Float voltages.

[Handmade Matt]

Understood. The German made Steca MPPT will be delivered tomorrow... Plain sailing from then on I reckon.
Thanks everyone. A great first experience from the forum.
All the best.

[RussN9ZP]

My charge controller is a cheap Chinese unit bought on eBay.
I've already decided to send it back, it's pretty yucky. You can see it here:
http://www.ebay.co.uk/itm/2610074254...#ht_6481wt_986

It claims to be MPPT but I'm doubting it already.
It's putting out less amps than it's getting in.

I've just bought (under advice from a friend) this unit:
http://www.ebay.co.uk/itm/3006809817...#ht_1740wt_986
It's German made (Steca) and seems to be much better and will allow room for me to expand my array.

Be careful, there are imposter steca's out there also. A US seller was selling one that was not a true steca that i saw on there the other day.

[Handmade Matt]

That's interesting to know but I have full faith in my retailer.

knowyourplanet..com I used their eBay shop.



Mod Note, you cannot post active links to sales sites here.

[Handmade Matt]

Mod Note, you cannot post active links to sales sites here.[/QUOTE]
Understood.