DIY Electric Car Forums banner

1 - 10 of 10 Posts

·
Registered
Joined
·
140 Posts
Discussion Starter · #1 · (Edited)
HTML:
We don't usually try to do this on purpose, but we were barely going to make it home and just had to see how low it would go.

We have 12 marine deep cycle flooded cells in series. They are the cheapest and worst battery anyone can put in an EV. We plan to replace them someday, but we college students lack the funds.

How low have you sagged?

http://www.youtube.com/watch?v=e1oqeGYo8kU

 

·
Registered
Joined
·
2,217 Posts
When I ran 10 Optimas in my buggy for a 120 volt system I would sag the pack to about 75 volts the last year before I replaced the pack. That was where my DC to DC would cut out and the main contactor would open. Just a few such stunts pretty much ruins a pack.
 

·
Registered
Joined
·
440 Posts
When I first got my Yaris (sold to me with 14 bad Optima batteries) I got 10 miles then voltage dropped from 178V to as low as 110v. I crept along to get home until the amperage as well diminished. (I suspect the zilla had something to do with it.) So there is really nothing left under resting voltage of 140 and sag voltage of 110v in the 14x12v batteries.

With the amount of sag you have maybe you have some bad connections or several batteries that are shorted and only have a surface charge.

francis
 

·
Registered
Joined
·
78 Posts
Running below the rated low voltage keeps the Lead & battery CEOs yachts in wonderfull condition.

As the voltage drops and the workload remains the same. The amperage has to climb.
That starts a death cycle of heating in various parts of the drive system.

Think of shoveling dry snow as it is falling at a rate of 1 shovel full per second. Now what do you do and say when it changes to very wet snow ?

Yes sir.
" huff & puff, You are KILLING ME ! STOP IT at this pace !!!"

Same thing the electric parts are screaming at you.
 

·
Registered
Joined
·
78 Posts
Jimbo

I hope you checked the water levels in every cell once the batteries cooled down. Then added enough to just cover the cell plates. Then did a slow charge rate, recharge. Finally refilled all the cells again after the batteries were at room temperature.

Be EXTREMLY thankfull you were using true Lead, flooded cell , deep cycle batteries. I do not know of any other type of battery chemistery that would take that abuse & say, thank you.
OK maybe A123 LIFEPO4 also. I have run them down to 5% many times. But never with that high of a current overload.

Your EV is one fantastic vehicle. :) I would give it a complete recheck. Electrical & mechanical retightening.
 

·
Registered
Joined
·
1,900 Posts
I've been to 80V as that is the cutoff of the Curtis 1231C I believe. Whatever it is, I've been there! Occasionally I go to about 110 but I try to limit my trips so I'm safely in reach of home.

BTW I've got over 8000 miles on my set. I had to replace one but it just died abruptly, while sitting at the office after the charge completed! Have no idea what happened. The truck still gets over 30 miles as it did when they were new.
 

·
Registered
Joined
·
299 Posts
I've gotten all my batteries from the battery of the month club so I have all different vintages of the same battery. Every time I over sag mine, I find out which one is the weak link. Seems to work like a fuse for the remaining batteries. :)
 

·
Registered
Joined
·
140 Posts
Discussion Starter · #9 ·
We have checked water levels and filled the cells, also tested PH on them a few months ago.

They weren't actually that far from original condition. Although, our range is kind of shot. We used to get about 20miles a charge. Now, I think I can get 10 normally, and 15 miles if I drive like a grandma.

The connections have all been checked and tightened (had to remove the batteries when an overcharge cause an acid overflow). Our 4/0 cabling and connectors should be more then sufficient for this current draw.

I am very surprised our logisystems hasn't cut out on us at this voltage. There must be no low voltage cut-off. The usual problem is that the dc-dc does not maintain a high enough voltage to keep the contactor on.

I think the car/batteries only have a couple hundred EV miles on them. I wish we wouldn't have skimped but spent a few hundred extra on real traction batteries (those purchasing parts should take this advice!).

I don't plan on putting anymore money into lead (or this car). Next project will be lithium with bms in a new vehicle.
 

·
Registered
Joined
·
1,317 Posts
I would suspect that there is something wrong with the voltage measurement setup or how it is installed. I've abused some lead acid batteries in the past and they simply don't sag like that while being able to put out any kind of current.
 
1 - 10 of 10 Posts
Top