Most cost effective 12v highest a/h lithium battery setup.

Apologies for being pretty much "off forum" with this, but the accumulated knowledge base on here is the best resource I can think of to find the answer to a project I've been mulling over for some time now.

 

I know I've touched on the question on here before, but I confess I didn't fully understand the answers, as my grasp of individual lithium cells ( 2p4s etc) is still limited.

 

After my disastrous purchase of the 12v lithium motor bike battery and then finding out what PbEq meant, I'd now like to try doing the job properly !

 

I have a very lightweight 12v electric outboard motor that I use on my sit on top kayak, and I'd like to upgrade the present 12v 28amp SLA battery pack with lithium. (it's two 12v 14ah SLA in series, weighing 8 kg total).

 

I'd like to build a 12v lithium battery pack (iron or lipo) with BMS and charger, with the most cost effective a/h capacity, (ie, most bang for bucks )

 

It would be nice to get the a/h as high as possible without getting heavier.

 

I always get hammered for import duty and "collection fees", so a UK or European supplier would be preferred, but not if the Chinese price is vastly cheaper.

 

What parts exactly do I need to order, and from who ? (please).

RC Lipo probably gets you the most bang for your buck, and the great thing about boats is that fires are self extinguishing!

 

While I can't tell you much about the parts, I can tell you that you only need about 14ah to be somewhere near your existing 28ah SLA.

 

I assume that was a typo in your post, and that you mean 2 x 14ah, 12v in parallel, which will give you 12v, 28ah.

Wow, that was quick Mike, thanks for the reply.

Yes, I meant that my present SLA pack is 12v 28 a/h.

They are deep cycle too, so I would think I can go down below the 50% max discharge for ordinary lead acid ? (though I'm ready to be corrected !)

As far as I understand it, deep cycle means that they can tolerate being deep cycled more often, not that they give a lot more energy.

 

I was just looking at Hobby King, they have RC Lipo packs at 4s (14.8v) 5ah, £22 each. If you had 4, you would get 20ah, and a slightly higher voltage. You might be able to get the 'yak up on the plane!

 

You will need a charger, and wiring harnesses etc, perhaps others can advise on that.

3S is 9v to 12.6v

4S is 12V to 16.8v

 

I've been running my electric outboard at 3S, but it seems a bit gutless, especially as the cells sag a bit due to the high current, so I think 4S would be better. I made by battery from a 36v ebike one. It was 10S6P 18650s. I reconfigured it to 3S18P because I need about 30 amps. I charge it with a lipo charger and use a lipo alarm to make sure that I don't over-drain it.

 

If you want to go with 4S, theses are cheap and convenient. Two or three in parallel should do it.

http://www.hobbyking.co.uk/hobbyking/store/__26801__Turnigy_5000mAh_4S1P_14_8v_20C_hardcase_pack_UK_Warehouse_.html?strSearch=4s%20hard

 

You can use these to add up to 6 in parallel;

http://www.hobbyking.co.uk/hobbyking/store/__45752__JST_XH_Parallel_Balance_Lead_4S_250mm_6xJST_XH_UK_Warehouse_.html?strSearch=parallel%20balance

 

and three of these for 4 packs in parallel:

http://www.hobbyking.co.uk/hobbyking/store/__26090__HXT4mm_Battery_Harness_14AWG_for_2_Packs_in_Parallel_UK_Warehouse_.html

 

lipo alarm

http://www.ebay.co.uk/itm/1S-8S-RC-Lipo-Battery-Low-Voltage-Alarm-Buzzer-Indicator-Meter-Checker-Tester-UK-/360623491533?pt=UK_ToysGames_RadioControlled_JN&hash=item53f6d5c9cd

 

If you want to stick with 3S, you could use these, which are a bit more expensive!

http://www.hobbyking.co.uk/hobbyking/store/__14083__ZIPPY_Flightmax_5000mAh_3S1P_20C_hardcase_pack.html?strSearch=3s%20hard

Thanks for the detail, I'll work my way through it and get back.

I've been studying the Hobby King kit as suggested by Mike and Dave, and I can understand the battery cells and connecting leads, as in this diagram:

So I believe that leaves the 12v charger (for lithium), how does that hook up to the JST-XH harness, and what model is needed ?

 

Also, is there a more automatic and integrated way of controlling the LVC than the low voltage alarm that Dave's linked to ?

 

20 ah of usable current per charge for around £75 and weighing just over 2kg does sound great for the outboard in a canoe.

 

How do these Hobby King packs compare with using individual Lipo cells and a dedicated BMS (if one exists for 12v), like other people have built on here for 36 and 48 volt bike packs ?

 

As Hobby King seem to have UK despatch, are they therefore quick and free from Customs duty and extra VAT charges?

 

Sorry again if my questions seem a bit naive again, but I have no experience with building battery packs.

No customs charges for Hobbyking UK stuff.

 

Charger is a matter of personal preference. I like the BC168 because it charges through the balance leads, which is useful for other congigurations, but is no advantage for yours. The iMax chargers are cheap and chearful, but are not 100% reliable. There's real ones, copies and copies of copies. The real ones from Hobbyking are probably OK.

 

The hardcase lipos are a lot safer than normal ones because you can't squish or puncture them. They've also got some protection if you drop them.

 

Your picture shows exactly what you need.

I used those Hobbyking batteries, £15 each.

 

You need a Lipo charger, also available at Hobbyking.

 

http://hobbyking.com/hobbyking/store/uh_listCategoriesAndProducts.asp?cwhl=GB&idCategory=216&v=&sortlist=H&LiPoConfig=

 

I use a few; here's one of the ones I use:

 

http://hobbyking.com/hobbyking/store/__25406__Turnigy_Accucel_6_50W_6A_Balancer_Charger_w_accessories_UK_Warehouse_.html

 

Any charger will do, but it must be cabable of charging 4s; the cheapest on I saw was £9. You'll need a 12 volt power supply to power it; I use an old PC power supply, so zero cost to me. If you need to buy a power supply, look here:

 

http://hobbyking.com/hobbyking/store/__467__408__Chargers_Accessories-Power_Supply.html

 

Costs £9

 

You can also get a parallel charging board, about £6. That will let you charge up to six patteries at once. When you see it, and look at the batteries, it's obvious how you connect the batteries to the charging board.

 

.http://hobbyking.com/hobbyking/store/__44570__Hobbyking_Parallel_charging_Board_for_6_packs_2_6S_HXT4mm_UK_Warehouse_.html

 

I'd recommend the low voltage alarm, that's what I use. You can also have a spare extra battery, so that when your alarm tells you that the battery is depleted, you aren't stranded.

 

You can use a parallel battery harness to link the batteries together, or you can do what I do, which is to use them one at a time, and when one battery it exhausted, plug in the next one. I like that, because it gives me a very accurate idea of what I have left.

 

If you order from the UK warehouse, there's no customs duty, and VAT is included in the price you see. But you have to check availability, and order as soon as they have the batteries in stock.

He doesn't need a parallel charging board because they'll already be in parallel.

This is true. Unless he uses the batteries one at a time like I do, and doesn't get the parallel harnesses or parallel balance six-way.

Thanks Dave and DrSolly, it's getting clearer now.

 

No customs charges for Hobbyking UK stuff...

and

If you order from the UK warehouse, there's no customs duty, and VAT is included in the price you see. But you have to check availability, and order as soon as they have the batteries in stock.

 

Excellent.

 

I like the BC168 because it charges through the balance leads..

 

It looks like a versatile charger for lithium pack charging. I couldn't find it on the Hobbyking site and then googled it and couldn't find a UK supplier, and the cheapest I could find was "RcEchoUK" from Hong Kong at £51.90 plus duty, that is going to almost double my current 20 a/h project outlay though.

 

The iMax chargers are cheap and chearful, but are not 100% reliable.There's real ones, copies and copies of copies. The real ones from Hobbyking are probably OK

...and DrSolly's

You need a Lipo charger, also available at Hobbyking. I use a few; here's one of the ones I use:

http://hobbyking.com/hobbyking/stor...ncer_Charger_w_accessories_UK_Warehouse_.html

 

Wow, £15.58, with no duty, that looks much more appealing !

 

The hardcase lipos are a lot safer than normal ones because you can't squish or puncture them. They've also got some protection if you drop them.

 

Yes, agreed, and it would be easy to bundle them up into one water resistant unit for the canoe.

 

I'd recommend the low voltage alarm, that's what I use.

 

You and Dave have recommended the same thing now, rather than a BMS to handle the LVC when the battery is in use. I guess as the charging is being handled in a sophisticated way with the balance leads and the charger, a normal BMS board would be largely redundant.

 

You can use a parallel battery harness to link the batteries together, or you can do what I do, which is to use them one at a time, and when one battery it exhausted, plug in the next one. I like that, because it gives me a very accurate idea of what I have left.

 

Yes, I can see some advantages there, but I suppose I need to check the max current draw from my outboard, to not exceed a single packs max output current ? Also, I was thinking of building one of those GT power meters into my "outboard pack", so that I could monitor the a/h used.

I got the BC168 recommended by d8veh and it's easy to use and good in that it displays individual cell voltages which I found helpful being a beginner to lipo's. I doubt you will get charged import duty on it either. You will also need a power supply for it, you could use a 12v laptop charger (probably only 2a though) or get a higher power one possibly 7a led light power supply off ebay for about £10, but I use this 15v one.

http://www.hobbyking.co.uk/hobbyking/store/__20971__Hobbyking_105W_15V_7A_Switching_DC_Power_Supply.html

Most lipo chargers need a 12v supply for which a PC power supply is ideal. You have to join a few wires on it. The BC168 is very useful for sorting out any ebike battery because you can charge and balance any number of cells up to 6 through the balance leads. If you only want it for lipos, it might be overkill.

 

It would be better to join your packs in parallel rather than use them one at a time. 5aH won't last long, and you'll be forever panicking about whether you've reached LVC as they sag up and down under the large current. With several joined up, there'll be less sag, less stress, less discharge (for each one) and a lot more time befor you have to start thinking about how much you used.

 

You can make/get an extension cable for the lipo alarm. It'll show individual cell voltages as well as the total, so it's easy to monitor usage; however, a wattmeter would be better.

I got the BC168 recommended by d8veh and it's easy to use and good in that it displays individual cell voltages which I found helpful being a beginner to lipo's. I doubt you will get charged import duty on it either

 

I always seem to get clobbered with duty and vat, and the "admin" charge as well !

The BC168 is very useful for sorting out any ebike battery because you can charge and balance any number of cells up to 6 through the balance leads.

 

I have to admit though that I am a sucker for "versatile" kit, just in case I get more packs etc..

 

Here's my version two schematic of everyone's suggestions, and I've upped it to 6 packs, giving me 30 a/h for around £130 plus the 12v PC power supply, (yes I've got a couple of those stashed somewhere, from when I upgraded to a quieter PSU in my PC!)

 

This would give me 30ah at 14.8v weighing just over 3 kg, compared to my existing pair of 12v 14ah SLA deep cycle batteries, giving 28ah and weighing 9kg, three times as much.

 

Am I right in assuming the usable ah from that 28ah SLA pair would be about 20ah ?, and the Hobbyking Lipos would give me the full 30 ah ?

 

Am I right in assuming that I need just one of those LVC alarms for my six pack battery ?

 

Looking at my diagram again, I've just realised I only need five HXT battery harnesses, rather than six.

I also got one of these cell checkers as well. It's not essential but I have found it really handy to double check cell voltages and give overall capacity left.

http://www.hobbyking.com/hobbyking/store/__43590__Turnigy_dlux_Auto_Checker_2_6S_LiPo_Battery_Checker_and_Balancer_UK_Warehouse_.html

Everything is correct. You only need one lipo alarm because all the cells will be in parallel just like 4 cells of six times the size, so you'll still have a four-cell battery.

Thanks for the link to the Hobbyking cell checker Awol, I'll put that on the shopping list. I must say, the prices are really good, especially coming from the UK with not import fees and delays etc..

 

Thanks for confirmation of the lipo alarm Dave.

Another thing has just occurred to me...

 

Would I be right in saying that if I sometimes connected the same six Hobbyking 14.8v 5a/h Lipo packs as two parallel banks of three in series, then I'd get a 44.4 volt 10a/h battery for my ebike ?

 

If that's practical, then it seems a cheap and versatile way to get that amount of power from a UK source ?

 

I'm assuming. that the balance leads stay the same for charging purposes with the dedicated charger, and just the output harness changes from 6P to 3S2P (have I got the hang of that now ?).

 

I suppose the LV alarm would still be needed, as the bike controller's LVC might be awkward for the 44.4v ?

The configuration at 12v would be 4S6P. To change it to 44v for an ebike, you reconfigure it as you suggested to 12S2P. Instead of the five parallel power leads, you'd only need three (3 x 4S2P). Then you need a series harness to connect them up to 44v. Ideally, you need a parallel balance lead (2 into 1) for each pair, and to monitor them, three lipo alarms.

 

You have to be more careful with charging lipos when you use them in a series configuration. It's a good idea to have a different connector on the final output to what's on the individual packs so that you don't get them mixed up. It's very important that you disconnect the packs from series before connecting your charger otherwise something will get vapourised.

Thanks Dave, I can understand the potential problems with them in series from what you say.

 

I did start thinking about maybe setting up keyed 8 way connectors with two different plugs as adapters prewired for the two configurations, but if it means three alarms then it's getting a bit Heath Robinson.

 

It's made it clearer how simple and fairly safe that the six in parallel will be though.

Another thing has just occurred to me...

 

Would I be right in saying that if I sometimes connected the same six Hobbyking 14.8v 5a/h Lipo packs as two parallel banks of three in series, then I'd get a 44.4 volt 10a/h battery for my ebike ?

 

 

Yup, that's idea and plenty do it. I would be a lot more reluctant to charge them in the house un-attended though.

 

I heard of one guy who charges his lipo's in an outside loo, on a plastic seat. His theory is that if it all catches fire, it'll melt the lid and drop through!

Yes Mike, I've noticed some of the precautions when I've googled R/C lipo charging on the Internet !

 

Quite a few people seem to use hollow concrete building blocks, a sort of scale model blast chamber...

Yes Mike, I've noticed some of the precautions when I've googled R/C lipo charging on the Internet !

 

Quite a few people seem to use hollow concrete building blocks, a sort of scale model blast chamber...

 

I will be using a lipo safety bag, similar to these.

http://www.ebay.co.uk/itm/Lipo-Safe-Charging-Bag-Safety-Fireproof-Charging-Sack-/151300990888?pt=UK_ToysGames_RadioControlled_JN&hash=item233a3de7a8

http://www.ebay.co.uk/itm/Lipo-Guard-Battery-Fireproof-Bag-Uk-Seller-9x11-5-23X30CM-/221460661541?pt=UK_ToysGames_RadioControlled_JN&hash=item3390158525