36v vs 48v performance

[mrphilf]

In a discussion with Vic at D&D last year he mentioned to me that in a 36 volt system on a full charge I shouldnt see my voltage drop below 33v on flat and not below 31v on hills. If so my batteries were junk, which they were.

Does anyone know what these numbers should be for a 48v system?

I just installed new Trojan T875's and am reading 50.9v sitting. Took it on a quick test run and was dropping to 44-45v on flat and 42v on hills. Is it normal to see this much drop in voltage? Will it get better as the batteries break in?

[kernal]

You should not let the batteries drop below 1.75v per cell. So 31.5v for a 36v pack and 42v for a 48v pack.

[Knothead]

You don't want to pull them down below 42 volts. You will damage your batteries if pulled down below 42v.......

If you have brand-new batteries, you need to follow ScottyB's break-in procedure found at www.cartsunlimited.com

They should get better after initial break-in, IF you don't damage them by not properly breaking them in.....

[mrphilf]

I only rode them for less than 2 minutes, its too cold to ride today lol. Just pulled one hill and did one straight away and they are at full charge.

I had found and used Scottys break in procedure on my 36v's before and was planning to use it again.

[Olman]

Did the upgrade to 48v meet your expectations? Mine sure did.

[mrphilf]

Haven't been able to tell, too cold to go out and really get on it today. Plus I wanted to check the battery voltage drop and see what folks here had to say before I really tried to pull a hill. Like I said above I pulled a little hill in my yard and my voltage dropped to 42, that was pretty disappointing. I hope its just because the batteries aren't broken in yet. If not, than my brandy new Trojans arent worth any more than Sams club junk

[cgtech]

Some may disagree, but, i feel it is pretty common with a bigger controller, for voltage to VERY BRIEFLY go below 42v under hard acceleration. Sustained operation below 42v will surely shorten the battery lifespan.

[Sumner121]

CGtech I totally agree, If I slam the accelerator from a standstill my batteries will just briefly (1 second) read 41.5 or so then quickly climb back up to between 46-48 depending on the load. Not sure how bad it is for them to do that, I'm sure it doesn't necessarily hurt them if it just dropping for the second. Under normal scenarios I would try to avoid the quick acceleration, but I've only had the 48 volt conversion for about 2 weeks and I'm completely in love with the new power I have at my disposal

[JohnnieB]

Here is the nitty-gritty on Under-load battery voltages.

The more amps you draw from a battery, the lower the voltage will drop.
How far it drops depends on the battery's AH capacity and SoC (State of Charge)
The temperature of the electrolyte is a factor in effective AH capacity, so the battery voltage drops more under load in cold weather.

Since battery manufacturers typically do not load their products below 1.75VPC (Volts per Cell) during non-destructive testing, trying not to routinely drop the voltage of your battery pack below 1.75VPC is a logical goal, but only a goal rather than an absolute.

1.75VPC = 31.50V for a 36V pack
1.75VPC = 36.75V for a 42V pack
1.75VPC = 42.00V for a 48V pack

Irreversible physical damage to the plates can occur when a battery is loaded down below 1.50VPC, so the following is the absolute lowest voltage your pack should ever be loaded down to.

1.50VPC = 27.00V for a 36V pack
1.50VPC = 31.50V for a 42V pack
1.50VPC = 36.00V for a 48V pack

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When I first installed a DCX500 and D&D motor, I could take my fully charged 245AH 42V pack down to 32V during a max effort acceleration from a standstill, so I adjusted the throttle up rate to give the motor a few moments to spin up some before the PWM output of the controller reached a 100% duty cycle.

[JohnnieB]

Originally Posted by Sumner121

CGtech I totally agree, If I slam the accelerator from a standstill my batteries will just briefly (1 second) read 41.5 or so then quickly climb back up to between 46-48 depending on the load. Not sure how bad it is for them to do that, I'm sure it doesn't necessarily hurt them if it just dropping for the second. Under normal scenarios I would try to avoid the quick acceleration, but I've only had the 48 volt conversion for about 2 weeks and I'm completely in love with the new power I have at my disposal

Treat them gentle until they are broken in.

They probably won't drop that far after they are broken in, and they won't drop that far in warmer weather.

The only time your motor can draw the max amps the controller will pass is when the motor is stalled, or spinning at very low RPM and that only happens when taking off from a standstill or when the cart is bogged down to walking speed or less on a steep hill.

You also have to be careful on the way home from a trip. The SoC will be lower, so the voltage will drop further with the same amp load.