So when attempting a quick battery change last night I managed to plug the ‘fresh’ LifePo4 Zippy Flightmax 4.2AH into the old one rather than the radio.
I soon realised my mistake and disconnected them. I was expecting melted connectors or cables but they didn’t appear to be harmed. As it happens the ‘fresh’ battery wasn’t fully charged and was showing a similar voltage to the one being replaced, so I think I just lucked out in that the voltage differential was quite small.
That then got me thinking about what you do when jump starting a car, connecting a 13.8v battery to a 12v battery and I then confused myself as to whether doing what I did actually wasn’t so dangerous. Anyway, it was out of character the way in which I was swapping the batteries over and I’ll try and keep to my usual practice of putting the old one away before fishing out the new one in future.
I don’t use them because they seem very expensive to me and I had lots of Tyton T connectors available from when we cleaned out a workshop being closed at work. Free is always good. And you cannot do this either!
I have one Powerpole to Tyton T connector lead so I can use other people’s batteries etc. I remember feeling my wallet had been abused and assualted when I bought that and another Powerpole!
Fuses in the battery leads are what I need. The rigs are protected with fuses but of course that doesn’t protect the batteries when this situation happens!
Hi Paul @G4MD,
Some Eaton UPS devices have Anderson PP fitted, so whenever I replace the batteries, I snip off the cables with PP connectors, before the batteries go for recycling. It does mean joining the cables with crimps/fitting appropriate connections at the other end of the cable, but it’s worked well for me.
Many of the bigger APC series UPS devices come with a larger version of the Anderson PPs - they are grey and much fatter. I’ve used these on things that draw more current (think 180w amplifiers using ~30A).
73, Simon
It happens to the best of us. I managed to do this with the 2 of my 3-cell LiPo batteries in the middle of a contest. It made a yellow flash and some black smoke and the connectors melted. The batteries seem to be ok
I guess the only thing of advantage of lithium batteries is the current available is so high that you are likely to knacker connectors or cables before the batteries…
I frequently plug my LiFePo batteries to each other in parallel in order to provide a clean 80 w signal even at -10 C. However, I usually take care that both are fully loaded. Anyway, the other day I didn’t charge one of them before attaching it to the other fully-loaded one: Great activation, lots of QSOs and no issues.
The partly discharged battery would have been drawing current from the other one. But each can source many amps.
As LiFePO4 batteries are typically rated 20C, this means each each can source their capacity in AH multiplied by 20. So a 4.2AH battery can supply 20 x 4.2 amps = 84 amps. They are used in RC aircraft to accelerate them in a continuous climb of several hundred metres. Or accelerate a RC car up to amazing speeds very quickly.
So if your radio plus amplifier requires 160 Amps, I can understand why you would connect two in parallel. This does not seem likely.
13v x 160 amps = 1780 watts, allocate about 200 of this for the radio and you have capacity to run an amplifier producing about 800 watts. In this case the battery would be much lighter than the amplifier, which will need a heat sink and fan to dissipate 800 watts as they are rarely better than 50% efficient.
I can sympathise with users more familiar with lead acid batteries, they will look at the small 4.2 AH lifepo4 and think they would never power a radio needing ten amps. But in fact they are capable of that and much more. This is why they are so dangerous and fuses or circuit breakers are so important.
I’m about to buy another circuit breaker for a new battery lead.
(theoretically - in practice less, nominal capacity is usually stated at a discharge rate of 1C or less, effective capacity is reduced at higher discharge rates)
you’re absolutely right. But take the freezing temperatures into account. If you draw more than 0,5 C then, the voltage will drop, means the battery can’t provide the needed peak current and an ssb signal will get splattered. Another thing is the Euro Tuesday VHF activity night that always goes for four hours. I want my batteries to last a complete Tuesday night, even in winter.
Ahoj
Pom
ok/dg7acf
PS: What I didn’t tell you, I use BMS’s with both batteries. They hopefully save the batteries from too high charging currents.
Use of BMS’s makes a lot of sense in this situation, and I suspect you have used this tactic based on experience of single battery operation!
All very interesting stuff.
With reference to circuit breakers, this isn’t something I’ve considered, I’m assuming you are talking about a device that can be reset rather than having to replace a fuse. What do you use?
Enough time to melt wire or worse. Yes it is not practical to run a high power rig from a small battery except to prove it works.
My point is that before connecting batteries in parallel we always need to consider what we are doing and whether the connection is going to do what we want or hope.
That’s the beauty of LiFePO4 batteries. They have an initial fall in voltage from a full charge and then the voltage is stable for a long period. I’ve been running a 4AH pack on a Youkits HB1A for the best part of a week and most of that time it has been sat between 13.4V and 13.2V. It will be interesting to see how much capacity I have used when I recharge it.
As for Powerpoles, I use them for all my portable rigs and even on some of my link dipoles. What is the cost compared to the cost of fuel to get to the summits? I always solder mine rather than crimp, so they are easy to re-use and I’ve never had a failure.
I do like that facility on my new B6AC charger. I’m trying out using 18650 cells recovered from scrap laptop packs at present and it’s nice to be able to see the reported charge values. I’ve just scrapped an add on second battery and expected to find a few dead and a few poor condition cells. But it looks like the charge regulator was gubbed and I have recovered 12x 1800mAh 18650 cells in it all in tiptop condition.
1800mAh is a bit weedy but 3 of them powered the 817 on HF for 30mins then the 2.3GHz transverter for another 25mins (through a step converter to get the volts up to 13.6V, 817 on a LiFePO cell). The B6 said the total current to get them fully charged again was 550mA which seems not bad if I understand it right. So there was plenty of life left. 3x 1800mAh cells and a cell holder + wires weighs 220gm.
and don’t forget to pack a few spares of the right rating 
