12v and 6v lead-acid in series for T200 for electric boat drive

Blue Robotics Products Batteries and Chargers
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Hi all,

I see from other posts that the T200 is happiest with about 18v for its power supply (sorry, not sure where I saw that, so much very good advice here)?

So, I’m thinking of using two T200s either side of the keel of a small (15-foot / 4.5m) wooden boat … it’s light plywood.

Could I put a 12v and a 6v lead-acid battery in series to power the trusters via the Thruster Commander? If so, any issues?

Advice appreciated, CaptainK

PS: I’m in the UK so before ordering a delivery from USA I’d like to make sure I’m getting the right stuff!

PPS: Yea, right Brexit and everything … ;-(

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Hi Patrick,
Although you can mix lead acid batteries without much hassle, it would probably be best to stick to 2x 12v batteries and add on a voltage regulator, that way you will have an equal drain on both and don’t have different charge times etc,
Being in the UK for parts give Buccaneer a ring, they stock most blue robotics parts (or can probably get them faster and cheaper anyway) Ian and William are great and always helped me out in the past when I was working with my previous employer’s Bluerov2

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Hi @captainkephart,

Really depends what you mean with this. If you take a look at the T200 Technical Details you can see from the performance charts that higher voltage increases the output power, but also increases the current draw and reduces the overall efficiency. Running at 20V gives ~2.3x higher maximum thrust than at 10V, but doing so uses ~4.6x more power.

Joining batteries is always a case of “the weakest link rules”. It may be fine if the batteries are well-matched, but if they’re not then there can be a variety of different issues, depending on their differences and how they’re connected. For series connections the main problems are related to capacity and discharge/charge rates - if one battery runs out then no current can pass, and the slowest battery is the one that determines the charge/discharge rate.

The upshot is basically that matching batteries is easiest when they’re two of exactly the same type (as @murf suggested), but it’s not impossible to work around, it’s just more complicated than “plug together et voilà”, and tends to age/degrade the batteries faster than standard use.

If you’re interested, there’s a decent explanation of the various considerations and concerns here :slight_smile:

My other main concern would be on discharge capacity. In particular, take note of the current your battery(/batteries) can supply for an extended period, compared with the current the T200s will draw at a given voltage + input signal.

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Hi Murf and Eliot,

That’s all really helpful, thanks for answering so quickly. Have read through … all makes good sense, but …

Can I give a bit of background as to where I’m coming from. Sorry, don’t wish to take up too much time, it’s gotten rather long.

My original idea was battery + throttle (variable resistor?) + motors, some wires, connect together, easy!
See one of my recent boats here.

This simple view was based on being familiar with auto / motorcycle electrical systems since the 1960s (I was even making transistor radios with discrete components then). But then I saw the T200, ah …

80s / 90s my professional work was in computing, mostly software, so the whole power electronic stuff that T200 uses passed me by (I remember seeing a huge cabinet, that had once housed a large mercury-arc glass rectifier, replaced with a small plastic block - I couldn’t get my head round why it didn’t just melt with the current).

I’m wary because, recently, I made a control system for charging 12v lead-acid batteries from two 135w solar panels and got in a mess. I hadn’t appreciated that the controllers were pulsing the power lines to send signals to each other and that these were confusing the USB step-down chargers I was connecting to the batteries.

So, Blue Robotics powered boat then. I realise I don’t need ESCs (?) as I’d like to control the T200s ‘directly’ with a mechanical throttle. I can see now that something like the Thruster Commander is best between throttle, battery(ies) and T200s. But:

  • What kind of thing would do for the ‘mechanical’ throttle that’s not one of the devices shown in the Technical Specifications?

  • Do I have to use an ESC? I’m guessing the Thruster Commander replaces that?

  • I’m not understanding where the battery voltage controllers sit in the circuit, or even what type to buy - especially want to avoid the cheap ones;

  • I’d like to use 2 identical 12v ‘leisure’ batteries in series for simplicity (trying to avoid the mini-computer that sits inside every Lithium battery) … though understand from the power curves that 2 in parallel gives a thrust / endurance trade-off;

Looking at other non-RoV DIY posts, some folks seem to be getting into a mess and short-circuiting things.

So, to avoid joining their numbers (!), have you produced any pages with sets of sample circuits for different applications to study?

Thanks so much … apologies if this has already been clearly answered somewhere!

Ciao, CaptainK

PS: murf, thanks for the tip, I’ll ring Buccaneer when I understand better what to ask for! :wink:

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One aspect to consider is the current the t200 need. It is not a trivial amount and the reason why LiPo battery are preferred to typical 12volts battery I think
For example, I need a 80amp relay just to have a on/off switch on my 8 thruster Rov. 80 amp rating or above!!
The voltage regulator you might need to scale down 24v to say 18v will be big I think. Maybe 30amps for 2x t200? The wires gauge is also important.
Maybe I am wrong and honestly I don’t have a lot of experience with T200 but I think that lead acid on it own, in parallel or serial configuration is not really an option unless you plan to mount a 100 amp battery pack or more. And this might be heavy to move around for the T200?

Charles

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Hi Charles,

Thanks for the advice, these are the issues I’m puzzling over, so all suggestions helpful.

It’s for powering a small boat so the weight of a 100Ah battery (or two) would not be a problem (good ballast!).

So 80amp on your 8 thruster RoV is 10amps per thruster in effect …

On mine with 2 thrusters heavy duty car headlight relays might be ok … need to start taking design calculations more seriously.

Thanks, CaptainK

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Based on the T200 spec link in previous message. Each T200 should peak at 24 amp (16 volts supply). In my configuration to be 100% electro-safe, 8 x 24 + 10% overhead margin = > 200 amp to run full time full throtle. Has you can see, my relay is overwhelm. But I doubt anybody in the ROV community can actually respect these numbers. We all assume that we will only run the ROV full throttle in burst mode for short period of time. We also assume that at worst only 4 motors will be full throttle while the 4 others (other axis) won’t turn. You go up and down or forward and backward.

From your big boat perspective, you will probably run them full throttle much more than a ROV. In this case, “electro-safe” calculation is mandatory I guess and I think you should design everything base on 50 amp minimum.

Another aspect to consider in lead acid battery is that they are not meant to transfer high amp for long period. You can cranck you car starter for 2-3 seconds and it is ok but you will kill you car battery if you cranck your car without stopping. Lipo are way better in that respect. They can output much more amp for longer period. You migth find out that the lead acid battery will die faster than you think because you overload them. To avoid this, you have to design a battery pack for which the amp drain represent only a small fraction of the power bank. If I assume you are running full throttle → 40-50 amp drain, than for this to be marginal, you will need a huge lead-acid powerbank. Will 200 amp be enough (only 4 times your draining requirement)? I don’t know. It will work for 2-3 hours but then you will have to recharge. How many discharge / recharge cycle this will sustain? I don’t know.

good luck

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Sounds interesting :slight_smile:

Brushless DC motors (like those used in our thrusters) operate by charging coils in a particular sequence to attract and turn a magnetic rotor - they won’t run without an ESC. The Thruster Commander can be used as a convenient way to send meaningful control signals to the ESCs without needing custom circuitry, custom code, or a full autopilot board.

The Thruster Commander applies a voltage across its input pins and measures the voltage in the middle. It comes with potentiometers (variable resistors) that act as a voltage-divider, and can be turned to make the middle voltage higher or lower.

I’m not sure what exactly you’re asking about/for here, but if you’re after for example a larger thing to turn then that could be achieved by just attaching a larger knob to the potentiometer.

As above, yes you still need ESCs (one for each thruster you want to control).

If you’re using some kind of voltage regulator it would serve as the load for the power supply (battery), and then you use its outputs as the supply for the actual load (e.g. your thruster commander + ESCs). Choosing a suitable type would be mostly dependent on your desired voltage input and output, and corresponding output current that you require.

2x12V in series gives 24V output, which would require some kind of regulation because T200s have a maximum supply voltage of 20V. 2x12V in parallel gives a 12V output with double the current capacity, and since running T200s at a lower voltage also reduces the current draw then that would indeed mean the batteries would last longer, although likely at the cost of a slower vehicle (lower power input → lower thrust output).

Blue Robotics only sells one battery at this point in time, and we don’t actively support using several at once, so we don’t have sample application circuits for different setups (lithium-ion batteries are finicky, which makes it difficult to support combining them).

I’m aware that one of our distributors (@seaview) sells a battery/power supply manager, which is discussed here (their webpage has some high-level connection diagrams, if that’s of interest) :slight_smile:

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Hi Eliot (and thanks to Charles too),

That’s all great, I’ve now got enough information and circuits to get started with some confidence.

Yes, the ‘mechanical throttle’ I refer to is the sort of thing you see on a regular boat. But I can see how to link something like that to a pulley on the potentiometer (the wonders of Lego!).

Oh, but one more question … assuming I’m going to stick to using two lead acid 12v batteries, then …

In this Thruster Commander diagram, could the power inputs to each of the ESCs thick cables come from one of the two 12v batteries?

I understand all the caveats above about batteries in parallel, but would doing it this way avoid having the two batteries feeding into one battery controller (which then powers the system in the ‘normal’ way)?

It would save me buying one more (non BlueRobotics) component.

I’ll let you know how I get on once I’ve contacted the supplier Buccaneer that murf suggested.

Thanks a lot, CaptainK

PS: Re the mercury arc rectified see here. They were 3 feet high or so and were shielded as they pumped out a heap of ultra-violet, rated at 500Amp or so …

We called them the ‘Mekon’ after the leader of the ‘Treens’ in the Dan Dare action comic!

Incidentally, our local TV shop was run by Mr Treen, so some joking came his way :smile:

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Haha, that’s really cool! I’d love to see a setup like that connected to some thrusters :slight_smile:
If it’s possible to disassemble then you may be able to put the potentiometer(s) inside it, but a pulley system should also work if it’s robust enough.

Yes that should work (each ESC would have an independent 12V supply), although if doing that you should still connect together the ground wires so that there’s a common reference for the signals from the commander, e.g.

image
image968×942 67.7 KB

A neat way of solving the problem, before semiconductors became widely used :slight_smile:

Haha, there’s always some fun to be had with names

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Hi Eliot,

Great, thanks so much. Very clear.

Captain K

PS: It was the common ground that caused to issue with the home-made solar battery charger system. Substitute solar panels for thrusters; ESCs for charger controllers and batteries then receiving charge not giving it.

Somehow the two solar controllers ‘resonated’ and their control signals interfered. I ended up taking away the common ground. That’s why I wanted to check, Thanks.

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