specific gravity hydrometers

9 Posts
Apr 8, 2010 09:20 pm
specific gravity hydrometers

I am seeking opinions and advise on SG hydrometers.
Are the digital ones better than the glass ones? What makes and models are the better/best ones. I'm looking for quality for the money. Is there a special hydrometer for each battery brand? I have eight Trojan L16h-AC batteries that I'm working with. any and all replies will be appreciated.
Thank You
Apr 16, 2010 06:09 am
Re: specific gravity hydrometers

Uhm, I don't know if this will help you, or not but!
I used to fret over my batteries. I never understood them really, until I was thumbing through a high school chemistry text book and came across the explanation of a flooded cell lead acid battery that stated; these batteries do not store electricity, they convert electrical energy into a chemical energy and store that until such time as electrical energy is needed and then its converted back into electricity. It even gave the chemical equation. 

I don't even use a hydrometer on my own battery bank anymore. I calculated my electric power needs for a 24 hour day/night period and sized the battery bank just a little more than 5 time larger. Then I sized the PV array to replace, what is typically used in that 24 hour period, in just one sunny day.
Oh, I also have a Bogart TM2020 battery monitor mounted in the wall right by the front door just above the light switches. http://www.bogartengineering.com/ It reminds me to equalize each month. Equalizing is as simple as pushing a button on the Trace C60 charge controller. When its done it resets itself.

Of course there is still the chore of topping of the battery bank with distilled water before the equalizing charge but that gives me time to inspect them for any possible problems and it all takes me about 20 minutes, once a month.

It all worked on a set of Trojan T-105's I had. I got a little better than 7 years of service out of them before they started showing signs of age. Hoping to get 20 to 25 years or better from the lastest set of Surette 530's.

One of if not the greatest means of increased longevity of a deep cycle battery bank is, shallow cycling.

Apr 16, 2010 11:13 am
Re: specific gravity hydrometers

*The purpose of a battery is to store chemical energy and to convert this chemical energy into electrical energy when the need arises.

*A voltaic cell develops a potential difference when electrodes of two different metals are immersed in an electrolyte.   One electrode accumulates a positive charge.   The potential difference is due to the difference in charge between the two electrodes.

*The chemical equation for a lead-acid battery during discharge is: . PbO2 Pb 2H2SO4 discharge ® 2PbSO4 2H2O

*The chemical equation for a lead-acid battery during charge is: PbO2 Pb 2H2SO4 charge ¬   2PbSO4 2H2O

*When a lead-acid battery is discharged, electrolyte and the active material on the plates of the battery are consumed to produce water and lead sulphate.

*When a lead-acid battery is charged, electrical energy is added to the battery, causing the water and lead sulphate to be consumed and produce electrolyte and active material.

*Since specific gravity of a lead-acid battery decreases proportionally during discharge, the value of specific gravity at any given time is an approximate indication of the battery’s state of charge.

The last one pretty much says it all, "an approximate indication." So, for me, if all I can get is an approximation anyway, I would just as soon not mess with the acid electolyte and go with the state of charge battery monitor. Of coarse, all of the other "bells and whistles" included on the Bogart TM2020 are a bit of a luxury but for no more than what I paid for it, they are worth it to me.
9 Posts
Apr 16, 2010 09:13 pm
Re: specific gravity hydrometers

Thank You for the reply. I will definitely look into the battery monitor Tm2020. I see they have two shunts that can be used with them. I agree with your thinking on the hydrometer. I perfer not to make a mess with the battery acid also.
On the Surette 530's what is the 20 amp/hr rating those batteries?
Thanks again, Ray
Apr 25, 2010 04:07 am
Re: specific gravity hydrometers

SERIES 4000. 6 - VOLT. 3 - CELL
Model Rolls S-530
Cap 100 Hour 1.75 VPC 530
Cap 20 Hour 1.75 VPC 400
Length (in) 12 1/4
Width (in) 7 1/8
Height (in) 16 3/4
Weight (lb) 130lb
Warranty 7 year

400 amphours at the 20 hour rate.

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