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Discussion Starter · #1 ·
I am working on electric conversion

i have 48v lipo batteries (16s) to drive 10hp dc motor
using a curtis 1205 dc controller and a 200A solenoid

when i press down on the throttle my voltage goes down from 52V down to 20v and then picks bakc up to 50 v and the motor starts to spin
sometimes it drops and doesnt recover

It was working fine before , start 2 days ago

Individual cells show voltage 3.3 to 3.8 volts

not sure if this is a symptom of a bad solenoid, dc controller, or whether the batteries are bad?
 

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I shouldn't hurt to bypass that solenoid as a test. Corrosion, worn contacts, etc could let voltage through but limit current. And it might get hot doing so too. Easy to try. But it is rather odd that voltage drops, picks up, and THEN spins. That sounds more like a controller issue.
 

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Discussion Starter · #6 ·
I did an electric conversion on a John Deere Gator, which is powered through solar panel the odd thing is that the battery Bank shows close to 50 volts but when I put my digital multimeter on the two large studs of the solenoid I get 7 volts

I called EVdrives and he said that the solenoid should have the same voltage across the big studs as the battery, and should only slightly drop when actuating, so then I thought maybe the line between the positive of the battery and the solenoid including the fuse had an issue but when I look at the fuse I had almost no resistance which suggests it should be fine, however the lead connecting to the positive of the battery looks like it's almost melted not sure if it could be causing anything


I guess the question is, did the solenoid guy give me the right hand information should be voltage across the two big studs be the same as the battery Bank
122487
 

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I don't recognize that connector. Do you have a photo of an undamaged one? Also photos of your batteries, wiring, and motor?
 

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Discussion Starter · #8 ·
They're just battery cables from AutoZone



122488




This is the solenoid I'm using , positive terminal of the battery Bank goes to the large post on the right side of the solenoid,

The batteries are lithium ion cells I don't have a picture of them but I will get one, the terminal on the top however was pretty large around 22 mm so that's why I had to use such a large battery cable I had to bore out
 

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Discussion Starter · #9 ·
I have attached a picture of my battery setup

48 volt 16 in series
122510


I have had a new development when I turn the inverter on which is also attached to the same battery pack I noticed that the pack voltage drops to around 10 volts does this mean my lithium ion batteries are all bad or perhaps just one?
 

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Discussion Starter · #10 ·
I noticed that the battery pack voltage shows 57 volts but when I connect my DC inverter suddenly the pack voltage drops to 10 volts does this mean I have somehow damaged by lithium-ion batteries?
 

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I would be suspect of the fuse or the solenoid. Something is causing a large voltage drop when a load is put on it. If your batteries were dead then they wouldn't show 57 volts unloaded.
 

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48 volt 16 in series
16 LiFePO4 cells in series at 3.2 volts (nominal) each is 50 V nominal, not 48.

I noticed that the battery pack voltage shows 57 volts but when I connect my DC inverter suddenly the pack voltage drops to 10 volts does this mean I have somehow damaged by lithium-ion batteries?
57 volts or 3.56 V per cell sounds reasonable for 16 fully charged LiFePO4 cells in series.

The voltage at the battery will drop due to a combination of current flowing from the battery and the internal resistance of the battery. If the drop is large the current is large, or the resistance is high (indicating a problem), or some combination. In this case it seems like there isn't any big load (the inverter is just turned on, not driving the motor), so there shouldn't be any significant current.

Do you have a precharge circuit? When the controller/inverter first gets power, the capacitors in it charge up. That can cause a large (but brief) surge of current, so a precharge circuit is normally used with resistor to reduce the current. Starting the inverter without proper precharge management could cause a large current surge and resulting voltage drop, but that should be brief and would not explain the acceleration problem.

Voltage at the input to the inverter will drop due to drops in the battery voltage, and the combination of current through the wiring and the resistance of the wiring. Bad contactor (solenoid, relay) contacts and corroded cable terminals could be sources of high resistance and thus low voltage at the inverter under load, but would not explain the recovery of voltage described in the first post.

I wonder about some fault in the capacitors within the inverter, but that's only a guess to consider when looking for possibilities.
 

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Discussion Starter · #13 ·
As a part of the mystery, I rechecked the voltage at the battery side of the solenoid and I got 57 volts but on the controller side it was 50 volts so I figured maybe the pre-charge resistor was the problem I removed that, and the car started to move 5 minutes later the battery pack showed 12 volts and incrementally started to increase, over the course of about 20 minutes to around 50 volts

Then when I turned on the inverter without any load the battery pack voltage drop to 10 volts

My biggest concern is that my lithium ion batteries are all bad, perhaps showing me a voltage but not having any capacity

My thought is perhaps the capacitors in the inverter is drawing all the voltage I'm asking the fact that my battery pack may have no amp hours

As far as a pre-charge resistor to the inverter I do not have one of those


In fact the whole system is rigged up with solar power , 1000w using a charge controller which automatically charges the batteries, regardless of whether I turned on the solar power or the inverter the pack voltage dropped significantly
 

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Let's get back to basics. What's the size of your battery and motor wiring? Are you using a BMS? Did you balance the charge of each cell to start? Your cells probably should be closer together than the 3.3-3.8V range you wrote in post 1. At 150-200 battery amps you need to have good size wiring and connectors, and clean, tight connections. Your wires between the controller and the motor should be as short as possible and possibly larger to handle amperage multiplication during acceleration.
Your controller is made for a series motor. Is that the type of motor you have? Again, more pictures would be helpful
 

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Discussion Starter · #15 ·
Let's get back to basics. What's the size of your battery and motor wiring?

I have 16 lithium ion 3.7v in series, around 50v

Are you using a BMS?

Unfortunately I did not use a BMS. They are connected in series but when I put the multimeter to the positive and negative of each individual one day rain between 3.3 to 3.8 volts, not sure if I have to disconnect each one and check them individually


Did you balance the charge of each cell to start? Your cells probably should be closer together than the 3.3-3.8V range you wrote in post 1. At 150-200 battery amps you need to have good size wiring and connectors, and clean, tight connections.

The lithium-ion batteries were rated as 3.7 volt 185 amp hours

Your wires between the controller and the motor should be as short as possible and possibly larger to handle amperage multiplication during acceleration.


The wires are approximately 4 ft long, in I'm using 6 gauge wire


Your controller is made for a series motor. Is that the type of motor you have? Again, more pictures would be helpful.

I am using a Curtis 1205 I believe it is a series controller
 

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Discussion Starter · #17 ·
Actually u right it's 4 gauge


I'm using a 36 volt, dc motor, my battery pack voltages higher, so I'm probably getting a little higher RPM
122511
 

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The batteries are lithium ion cells I don't have a picture of them but I will get one, the terminal on the top however was pretty large around 22 mm so that's why I had to use such a large battery cable I had to bore out
Your terminal mounting holes only need to be the diameter of the threaded portion of the clamping bolts, 8-10mm.

As far as a pre-charge resistor to the inverter I do not have one of those
The 470ohm resistor across the large terminals of the contactor in the picture, in post 8, is probably a precharge resistor.

Unfortunately I did not use a BMS. They are connected in series but when I put the multimeter to the positive and negative of each individual one day rain between 3.3 to 3.8 volts, not sure if I have to disconnect each one and check them individually
You can check and charge them individually,if you are careful, without disconnecting them. You have several thousand $ worth of batteries here. If I were you, I would monitor and protect them as my first priority. This means balancing their voltages and capacities to be as uniform as possible. This balancing process may reveal cell(s) that will hold a lower voltage and Ah capacity. The pack will only have as much Ah capacity as this lowest cell. If the capacity is really bad, consider removing or replacing the cell(s).
To maintain the cell balance, the monitoring and balancing needs to be repeated on a regular basis. Ths can be done manually or with a good BMS. A good BMS will save big bucks and a lot of work, in the long run.
I don't want to beat-up on you. But I cringe at some of your build quality. When working with high power systems, with a lot of electrical current, the conductors need to be sized properly and the connections need to clean and tight. I've worked with welding machines running at 300-400 amps, continuously. They preform poorly or blow-up right away if you are sloppy in these areas!
If you can show us more detailed pics of you set-up, we'll try not to be too picky or cynical about what we see!
 

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I have 16 lithium ion 3.7v in series, around 50v
...
The lithium-ion batteries were rated as 3.7 volt 185 amp hours
Was that 3.7 volt rating fully charged, or nominal? You described them at one point as "lipo" (which means lithium-polymer, meaning any chemistry with a polymer electrolyte) and the cells in the photo look like typical LiFePO4. What type of cells are these?
 

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Discussion Starter · #20 ·
These are lifepo4 batteries

They're supposed to be fully charged as currently my setup is attached to a solar array with the charge controller however I'm thinking the problem I'm having is that the charge controller may be picking up the voltage from the DC AC inverter or the capacitors in the DC controller and not allowing the batteries to actually be fully charged?

I'm not sure if that makes sense,
Your terminal mounting holes only need to be the diameter of the threaded portion of the clamping bolts, 8-10mm.



The 470ohm resistor across the large terminals of the contactor in the picture, in post 8, is probably a precharge resistor.


You can check and charge them individually,if you are careful, without disconnecting them. You have several thousand $ worth of batteries here. If I were you, I would monitor and protect them as my first priority. This means balancing their voltages and capacities to be as uniform as possible. This balancing process may reveal cell(s) that will hold a lower voltage and Ah capacity. The pack will only have as much Ah capacity as this lowest cell. If the capacity is really bad, consider removing or replacing the cell(s).
To maintain the cell balance, the monitoring and balancing needs to be repeated on a regular basis. Ths can be done manually or with a good BMS. A good BMS will save big bucks and a lot of work, in the long run.
I don't want to beat-up on you. But I cringe at some of your build quality. When working with high power systems, with a lot of electrical current, the conductors need to be sized properly and the connections need to clean and tight. I've worked with welding machines running at 300-400 amps, continuously. They preform poorly or blow-up right away if you are sloppy in these areas!
If you can show us more detailed pics of you set-up, we'll try not to be too picky or cynical about what we see!
I definitely am a newbie, did this project without much guidance, just some googling and YouTube, so please do criticize, so that I may learn.

I actually bought a BMS but haven't had the courage to put it on because of the mini Sparks I encountered putting the batteries together

I will try to take a video and post it so you can see the system
 
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