Battery Drops From 11.7V To 10.8V With Ciruict On? 1

[jmeyer84]

I'm using a "12V" lead acid battery to power a circuit of mine. When the battery is not connected to the circuit, the voltage I'm getting on a multimeter is about 11.7V. When the circuit is active and powered by the battery, it reads 10.8V.

Why is the battery losing almost a volt in potential only when powering my circuit?

 

[IRstuff]

As an electrical engineer, you should be familiar with series resistance, no?

TTFN

FAQ731-376

 

[ScottyUK]

Google "internal resistance". The wiki entry should be a starting point.

Oh, and your battery sounds like it needs a recharge. It should be somewhere just over 13V if it is in a decent state of charge.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[itsmoked]

Battery could be toast. How was it last charged?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jmeyer84]

The 11.7V value wasn't at a full charge. The battery was charged with a float charger, but I had been using it all day.

I'm somewhat familiar with internal resistance, and wikipedia says it's usually on the order of 50 mOhms for a lead acid battery. It seems like an awfully large drop.

The battery is older and has been used quite a lot. Is the large drop a sign that the battery is going bad?

 

[MacGyverS2000]

Would you say you were pulling close to 20A form the battery?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[jmeyer84]

300 to 400mA

 

[BobM3]

Bad connection to a corroded terminal?

 

[roydm]

At 11.7 volts for lead acid battery it's flat. The minimum voltage is 12.
It is possible you have a bad connection. The terminals will oxidize, Lead Oxide is an insulator.
The way to avoid a bad connection is to clean the connections (shiny lead) then coat the joint with Petroleum Jelly (Vaseline), this prevents the air getting at the metal,
no air = no oxygen,
no oxygen = no oxidation
Regards
Roy

 

[itsmoked]

Is this a "gel cell"? If it is there is a very good chance it's failed. Modern gel cells are extremely susceptible to being damaged by lack of charge. If you drain them below about 12V the damage builds up rapidly. One over-discharge is enough to toast a modern gel cell(VRLA) battery.

I've purchased one new, fully cycled it two or there times in two days, noting data sheet capacity, then had the device running from it over discharge it after hours. Next day the battery has 1/10th its original capacity - effectively destroyed.

Another time I let a brand new fully charged VRLA self discharge for a year. At the end of a year when I checked it it was at 11.8V it was NOT rechargeable. It had lost all capacity.

Modern VRLA batteries need to be treated with kid gloves.

Never let them get below 12V and if you do, fully charge them, IMMEDIATELY, not tomorrow, not later today, NOW!

Put a regular charger on yours not a trickle charger. See if it takes a charge.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

If you have an adjustable power supply, an ammeter, and tell us what battery you have, we can help you check this out.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jmeyer84]

The battery is a PowerSonic PSH-1280F2-FR:

http://www.power-sonic.com/site/doc/prod/139.pdf

I can't tell if it is gel-based, but it may have been drained and sat on a shelf for a couple months.

 

[itsmoked]

Ah, yeah...

You notice in the data sheet that it states "charge every six months or it will be damaged"?

It's damaged.

You can confirm this if you apply 14.4V to the battery and see less than about 2A of current flow. This would mean the battery is fully sulfated. D E A D.

BTW if you see more than 1.5A do not charge faster than this.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jmeyer84]

Thank you all so much.

I went to NAPA and got another one. No noticable drop now.

 

[itsmoked]

Thanks for the come-back.

Don't forget to keep it well charged.

Use one of these:

http://batterytender.com/chargers/battery-tender-junior-12v-at-0-75a.html

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Nice trouble shooting, Keith.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Cloud9TN]

We use loads of those powersonic gelcels. They are good for the price and the size, but they do have their downfalls. We often have bad batteries. Even in some cases, its good one day, bad the next. Especially if we leave the power on to one of our units that is powered by this battery, its trouble.

 

[itsmoked]

A good LA gel cell design HAS to cut off the drain to the battery while there is still a good percentage of charge remaining.

Then it needs to strenuously request charging. (Preferably something like a squeezed baby pig sound.)

If ever there was a battery that should NEVER be "ridden hard and put away wet", it's a GelCell.

Keith Cress
kcress -

http://www.flaminsystems.com