The Thomas A. Edison Papers Digital Edition

Transcription

April 26, 1901
Mr. Thomas A. Edison
Orange, N.J.
My dear Mr. Edison:
On my return from the Laboratory the other day, I reviewed the figures that I had given you, and found that there were two very serious mistakes.
I did not properly add the weight of the suphuric acid and water, and at the same time gave you the wrong rating of the battery in horse power. This last mistake is due to the fact that the battery people persistently rate their central station batteries at 110 volts pressure, although the batteries are for 220 volts, and therefore at this last pressure are good for only one half the current at which they are rated. Thus, a 14,000 ampere hour battery really means 700 amperes at 220 volts, or 1400 amperes at 110 volts. 
I enclose two memorandums which I have prepared carefully myself, and can state positively that they are correct. I have had the figures verified by actual weights of the different parts.
I regret exceedingly that this mistake occurred, but discovered it on my return, and your letter of April 24th served as an additional reminder. 
In charging the batteries, they are charged up at the normal rate (10 hour rate) until the voltage of each cell is 2.5. At the instant the batteries begin to discharge, the voltage of each cell drops to 2.1, and from that point slowly drops until we stop the discharging of the battery at 1.78, which is about as low as we can go economically. If the battery discharges below 1.78, the voltage drops very rapidly to zero, and then reverses. When the battery is discharged, the specific gravity is 1200; when the battery is discharged, it falls to 1165. The voltage between the electrolyte and the positive plate is mentioned in an article by MR. Jos. Appleton, in the Electrical Engineer of March 17, 24, 31, April 7, 14, 21 and 28, 1897. Our tests of voltage are made by introducing a cadmium plate between the positive and negative in the electrolyte. The following are the results:
At 10 hour rate, the readings at the beginning of discharge between the positive and negative plates are 2.10; between negative and cadmium .16; between positive and cadmium 2.26.. After five hours discharge at same rate the readings between positive negative plates are 1.94; between negative and cadmium .2; between positive and cadmium 2.14. At the end of the discharge, the readings between positive and negative plates are 1.74; between negative and cadmium .23; between positive and cadmium 1.97.
In checking the weights of the plates, which you will notice are much more than I gave you, I found that the plates which had been weighed, and which I told you averaged 27 lbs., when carefully examined, presented a curious appearance. The negative buttons had partly disintegrated, and the balance of the button had blistered so as to give the button the appearance of a solid button, although it was almost hollow. In weighing a larger number of plates, and carefully examining them, I was able to secure more reliable figures, showing the average weight per horse power which are herein enclosed are rather low, since from the plates about 30 tons of oxide has dropped to the bottom of the cells, and this we are now removing. This was not considered in the weights of the cells. 
As the battery wears out, the weight per cell for the same output drops, until the buttons of active material entirely disappear, when the capacity decreases so that the weight per horse power is increased enormously. 
I trust that you will pardon the mistake which was made, and that the enclosed information will be satisfactory. Should there be any test which you should like made for further information, I should be pleased to have it made and results sent to you, or should you desire to visit the batteries in question, I should be glad to arrange for such visit at any time.
W.S. Barstow MEMORANDUM OF SECOND DISTRICT BATTERY.
This battery consists of 140 cells, catalogued as Type H-#27.
Each cell contains 13 positive and 14 negative plates, each positive plate weighing 46 lbs., and each negative plate weighing 27 lbs., so that total weight of elements in each cell is 976 lbs. Added to this should be the lead connection connecting the elements together, the weight of which is 40 lbs., making total weight of 1016 lbs of lead, elements and connection.
The water and sulphuric acid (sp. gr. 1200) weighs 670 lbs.
The lead lined wooden cells weigh 350 lbs. each.
Total weight of cell complete.....2036
2036 lbs. x 140 cells=285,040 lbs. total weight of battery.
At 10 hour rate, battery gives 133 H.P. for 10 hours, at average voltage of each cell of 1.9.
At one hour rate, battery gives 644 H.P. for one hour at average voltage of 1.8 per cell.
Weight of battery per H.P.H. at 10 hour rate 214 lbs. 
Weight of battery per H.P.H. at one hour rate 460 lbs. MEMORANDUM OF SUBSTATION "A" BATTERY
This battery consists of 156 cells, catalogued as Type H-#51.
Each cell contains 25 positive and negative plates, each positive plate weighing 46 lbs., and each negative plate weighing 27 lbs., so that total weight of elements in each cell is 1852 lbs. Added to this should be the lead connection connecting the elements together, the weight of which is 46 lbs., making total weight of 1898 lbs. of lead, elements and connection. 
The water and sulphuric acid (sp. gr. 1200) weighs 1090 lbs. 
The lead lined wooden cells weigh 650 lbs. each.
Total weight of cell complete......3638 lbs. 
3638 lbs x 156+567,528 lbs. total weight of battery.
At 10 hour rate, battery gives 278 H.P. per hour for ten hours, at average voltage of each cell of 1.9.
At one hour rate, battery gives 278 H.P. per hour for one hour, at average voltage of each cell of 1.8.
Weight of battery per H.P.H. at 10 hour rate 204 lbs.
Weight of battery per H.P.H. at one hur rate 506 lbs.