What package and version are you using ?
Amiga chassis
Please, describe the issues you are seeing ?
Hello, I’m tasked with configuring an Amiga but it was assembled when I received it. I’m tracing cables to see how each motor connects to the CAN/power and e-stop buses. I noticed the DC terminals for one battery are not connected to the terminals for the other battery (see pic). This is the conduit going from the left side to the right side of the Amiga. However, obviously because all 4 motors are visible to the dashboard, the CAN/power bus from this conduit is connected.
All of our powered devices will be mounted on the right and I’m worried one battery will have greater load than another. Should I connect the batteries in parallel? Is the load already balanced through the CAN/power bus? Thank you.
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The existing batteries are already connected in parallel, and to keep the system simple we chose this path to avoid complexity and keep it flexible.
Ideally you connects packs in parallel that have the same voltage potential. For example just after charging, which significantly reduces any transient current spikes when connecting multiple batteries.
If there is enough voltage difference the transient current spikes could trigger the battery packs BMS to protect itself and disconnect the current path. It is unlikely but possible to blow the fuse.
The red and black Andersons are all in parallel so they should all act similar and connect to the same power bus.
I’m not sure if this question warrants a new topic, but I’m wondering about the viability of putting additional packs into parallel on the same bus. Namely, populating the other two battery slots with additional batteries.
Totally aware of the cell charge level mismatch on connection issue and we’d balance and measure OCV before plugging them in to minimize/eliminate any cross currents.
There is very little risk when the batteries are all charged to the same level and connected in parallel, as there is very little current flow between batteries. The risk is when there is a large mismatch between battery charge levels For example, you stick a fully charged battery along with a discharged battery. There will be a high current flow between batteries and potential for blowing a fuse or shutting off the BMS (battery management system). This is also a risk with the two battery system you already have.
Anyways, you should go for it if you need extended operational life from your Amiga. If you’re looking to buy more batteries and splitters directly from us, reach out at sales@farm-ng.com
Already have the battery kits, but am not clear on the documentation or wiring architecture, so this is mostly trying to make sure we don’t do anything that hurts the robot. I am planning on wiring all the batteries in parallel to 1. maximize traction runtime 2. run my auxilary load of 60-80W continuous draw off of the same rail. We can tolerate a very wide input swing from 36-60V on the input of our load so I am not concerned with pack swing from varying SOC.
Is it feasible to configure the system so that we can charge on the vehicle? Ideally I’d get the 4x individual chargers, wire them up into each battery’s input and then wye them into a single AC cord that we plug in to charge the whole works. Naturally we’d turn the robot off. I’d not rule out putting a contactor in series with the batteries and have it be switched by the AC input so that it automatically drops the load out when plugged in and only sees the batteries in parallel (like a delta-q quic charger does)
The biggest concern/rule is matching the packs voltage as much as possible before connecting. Small voltage differences will not be an issue, but matching a fully charged with a a fully discharged is a good way to blow fuses or tripping the BMS cutoffs. Plus you do not get the full benefit of parallel battery packs if they are not charged to the same level. So ideally you charge them all to the same voltage then connect them on the system.
Second biggest concern/rule is that you are adding capacity, but you cannot necessarily draw a lot more current (not adding power capability). This is because the limiting factor is connector and wire ratings. Adding a <100w load would not be a concern though.
I agree the battery operational range is between 38-51volts, and basically never goes outside of those ranges.
Charging on the vehicle is supported already, even with more than two packs, just be aware gain that you are adding capacity and not power capability. You would want a <800watt charger with a peak voltage 50.4vdc. Once the packs are in parallel they ideally stay in parallel, that way you avoid potential voltage differences from occurring. So something to watch out of is not turning all of the batteries on and/or off together, it is easy to only turn on some and forget cause an imbalance during use.
I would need to know more about the multiple chargers. We have a larger charger that can put out 5 amps and is setup to plug into the battery bus (the larger Anderson connectors) so that you do not have to pull the batteries out to charge. You might want to look into that if you do not have one already. Technically multiple of those could be added, but that somewhat depends on how you wire it.
This is a little bit of a brain dump, but hopefully this helps.
The biggest concern/rule is matching the packs voltage as much as possible before connecting. Small voltage differences will not be an issue, but matching a fully charged with a a fully discharged is a good way to blow fuses or tripping the BMS cutoffs. Plus you do not get the full benefit of parallel battery packs if they are not charged to the same level. So ideally you charge them all to the same voltage then connect them on the system. is there control circuitry to only let the high/low pack do work, or are we just talking about the high pack is going to feed the low pack and they will equalize with some charge inefficiency?
Second biggest concern/rule is that you are adding capacity, but you cannot necessarily draw a lot more current (not adding power capability). This is because the limiting factor is connector and wire ratings. Adding a <100w load would not be a concern though. understood, we are looking to only maximize runtime per cycle of the total pack
I agree the battery operational range is between 38-51volts, and basically never goes outside of those ranges.
Charging on the vehicle is supported already, even with more than two packs, just be aware gain that you are adding capacity and not power capability. You would want a <800watt charger with a peak voltage 50.4vdc. Once the packs are in parallel they ideally stay in parallel, that way you avoid potential voltage differences from occurring. So something to watch out of is not turning all of the batteries on and/or off together, it is easy to only turn on some and forget cause an imbalance during use. Do the chargers jump on the bus and feed whatever’s on there, or does the load get switched off somehow? It appears that we’re just dumping charger power onto the rail and the loads, if on and drawing power, can draw against that charge input and we’ll short cycle the packs (all the energy is eaten before the battery gets it)
I would need to know more about the multiple chargers. We have a larger charger that can put out 5 amps and is setup to plug into the battery bus (the larger Anderson connectors) so that you do not have to pull the batteries out to charge. You might want to look into that if you do not have one already. Technically multiple of those could be added, but that somewhat depends on how you wire it. I’m thinking mostly connect the AC input of one charger per battery or pair of batteries and make it so there’s a single input AC cord to plug in. It sounds like our operators don’t like the idea of having a hardwired charger on the vehicle because there’s no 110VAC available in the field anyways, so maybe this is a moot point. In an ideal world, I’d have something like a delta-q charger with the appropriate charge algorithm specifically for your batteries tuned to not exceed the charge limits of the parallel pack
Once the batteries are connected in parallel the current will flow and equalize the battery packs to the same voltage, once balanced with each other they should essentially act as one battery. The hope is to avoid large voltage differences which would cause the current flow to be high enough to cause issues. There is only protection circuitry in the battery, no high powered ideal diode system.
Since when the batteries are connected together, charging the bus will charge whatever batteries are connected. There will be some level of load sharing, and as long as the charger is charging higher than the system load currents when idle. Internally we leave a lot of the development machines plugged into a charger so the battery does not die while developing and sitting there, sometimes for days, and it does charge the batteries while this is happening. We have a charger that we sell that can provide this functionality.
We do have extra Anderson connectors on the Amiga for plugging into a charger without needing to change anything on the system. A delta-q charger can be used, depending on the power and voltage setting. If you are curious about if one would work I just would need to review the datasheet for it.
Delta-Q does custom algorithms based on battery specs. I am checking with my contact to see if they have or will make a generic algo that does 50.4V charge termination at no more than 2.5A per parallel pack. I suspect they’re going to be a little hesitant about the prospect of having multiple modules in parallel that don’t have telemetry to say yes/no if they’re plugged in because they will be blindly charging at (n of modules) * (charge limit per module) which can get back if you unplug or turn off one or more modules.
Hey Travis,
Just a quick question on the batteries. If accidentally one were to plug in a fully charged (51 V) battery to the system while a fully flat (38 V) battery was still plugged in, would that do a number on the motor controllers? I can’t see any fuses protecting the motor controllers? Any thoughts or recommendations?
Cheers, Ingrid
Overall the motor controllers are not sensitive to this issue. The motor controllers would only see a voltage input drop, as the battery packs balance themselves.
The worry is only on the batteries themselves, as the lower voltage pack becomes a load and has a high pulse of charge current, and the high voltage one has a high burst of discharge current. This could stress the cells, potential pop fuses (or trip BMS limits), as well as stress connectors and wires.
