Volts at WOT

rammunition361

got my digital meter installed. Whats normal reading at wide open throttle? Whats the number not to go below?

BGW

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JohnnieB

How far the pack voltage drops under load depends on how many amps your specific cart is placing on the battery pack at the time, the internal resistance of your specific batteries and the ambient temperature, in addition to the type motor being used and the RPM it is spinning at, plus a few other factors.

Try to stay above 1.75VPC (Volts per Cell) under load during normal operation and never drop the pack below 1.50VPC under load. (Irreversible physical damage occurs when you take them below 1.50VPC)

rammunition361

so even at wide open throttle it should never drop below 1.75vpc? with 38.5 volts at rest it dropped to 33.4

JohnnieB

1. The 1.75VPC is a recommendation rather than an absolute, while the 1.50VPC is an absolute.

When battery manufacturers do non-destructive testing of their products, they use 1.75VPC as the low end cutoff. When a Lead-Acid battery is loaded down to 1.50VPC and lower, the surface of the plates is sucked off.

2. Sounds like you have a 36V pack (Eighteen 2V cells), so you should strive to avoid taking the real time voltage reading of the DVM battery meter below 31.5V when accelerating from a standstill, towing/pushing stuff and climbing hills.

If you cannot avoid going below 31.5V, your battery pack is insufficient for your cart and the way you are using it.

Since it appears your setup will only take your well charged battery pack to 1.86VPC, you pack's capacity seems to be adequate. Of course, the voltage will drop lower when pack is partially discharged.

rammunition361

ok, just wanted to make sure the drop was ok. ive yet to put any real time in the seat cause its been real cold but I want it to be ready to go for the spring

rammunition361

ok I charged two days ago, when I got on cart today it read 38.8v, went to end of driveway and back and at wide open throttle I seen 30.6v. so im assuming at around 38v left I would drop below the absolute at wot. What do I need to do here?

JohnnieB

First, you need to learn what the absolute is.
(IE: 18 x 1.50V = 27.0V)

Second, your batteries appear to be dropping about 8.2V at WOT, you should not be discharging the pack below 50% before recharging and 50% SoC is an At-Rest voltage of 36.3V, so the lowest your cart's drive system will take your battery pack is about 28.1V, which is well above the 27.0V absolute minimum.

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It is possible you don't need to do anything, but an 8+ volt drop is a considerable amount, so you may want to verify the integrity and quality of the five cables connecting the six 6V batteries in series. Any excessive resistance in those cables and their connections, will increase the voltage drop seen.

To put it into perspective, an 8V drop is a bit much for a stock drive system, but the further your cart's drive system is away from stock tire height, stock controller ampacity and stock motor kW, the more likely it is to be normal for your cart.

rammunition361

haha I understand, I guess im just fearing for the worst and assuming with lower resting volts that im gonna drop quick at wot on a hill. If I see 30v full throttle with 38.8v resting on flat ground with one person on the cart, I cant imagine being able to go up any kind of incline with two people

JohnnieB

Something to keep in mind is that the only time your motor is electrically capable of drawing enough amps to drop your pack voltage into the danger zone is at low RPM (Under about 500RPM, but varies with set-up). Unless the incline is steep enough to drag the cart speed down to walking speed, you probably don't have anything to worry about.

Another thing to remember is the pack voltage drops fast under load, but recovers slowly. The 30.0V you are seeing on level ground is most likely due to a rapid start that took it down to ~30.0V and was very slowly climbing back towards a higher voltage as the motor RPM increased and amp draw decreased. Feather the throttle some for the first few yards off the line and the pack voltage won't drop quite as far.

Watching the pack voltage fluctuating all over the place is unsettling, but once you get a handle on why it happens, it is handy information to have in real time.

rammunition361

thank you very much. that eases my mind. the campsite is in Chillicothe, I grew up in wv. What part you from?